diff --git a/.coveragerc b/.coveragerc
new file mode 100644
index 0000000..d097511
--- /dev/null
+++ b/.coveragerc
@@ -0,0 +1,13 @@
+[run]
+branch = True
+
+[report]
+fail_under = 100
+show_missing = True
+exclude_lines =
+    # Re-enable the standard pragma
+    pragma: NO COVER
+    # Ignore debug-only repr
+    def __repr__
+    # Ignore abstract methods
+    raise NotImplementedError
diff --git a/.flake8 b/.flake8
new file mode 100644
index 0000000..3da787c
--- /dev/null
+++ b/.flake8
@@ -0,0 +1,11 @@
+[flake8]
+import-order-style=google
+# Note: this forces all google imports to be in the third group. See
+# https://github.com/PyCQA/flake8-import-order/issues/111
+application-import-names=google
+ignore = E203, E266, E501, W503
+exclude =
+  __pycache__,
+  .git,
+  *.pyc,
+  conf.py
diff --git a/.github/.OwlBot.lock.yaml b/.github/.OwlBot.lock.yaml
new file mode 100644
index 0000000..7519fa3
--- /dev/null
+++ b/.github/.OwlBot.lock.yaml
@@ -0,0 +1,3 @@
+docker:
+  image: gcr.io/cloud-devrel-public-resources/owlbot-python:latest
+  digest: sha256:0e18b9475fbeb12d9ad4302283171edebb6baf2dfca1bd215ee3b34ed79d95d7
diff --git a/.github/.OwlBot.yaml b/.github/.OwlBot.yaml
new file mode 100644
index 0000000..c8b40cc
--- /dev/null
+++ b/.github/.OwlBot.yaml
@@ -0,0 +1,19 @@
+# Copyright 2021 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+docker:
+  image: gcr.io/cloud-devrel-public-resources/owlbot-python:latest
+
+begin-after-commit-hash: 7af2cb8b2b725641ac0d07e2f256d453682802e6
+
diff --git a/.github/CODEOWNERS b/.github/CODEOWNERS
new file mode 100644
index 0000000..ee81891
--- /dev/null
+++ b/.github/CODEOWNERS
@@ -0,0 +1,12 @@
+# Code owners file.
+# This file controls who is tagged for review for any given pull request.
+#
+# For syntax help see:
+# https://help.github.com/en/github/creating-cloning-and-archiving-repositories/about-code-owners#codeowners-syntax
+# Note: This file is autogenerated. To make changes to the codeowner team, please update .repo-metadata.json.
+
+# @googleapis/yoshi-python @googleapis/actools-python are the default owners for changes in this repo
+*     @googleapis/yoshi-python @googleapis/actools-python
+
+# @googleapis/python-samples-owners @googleapis/actools-python are the default owners for samples changes
+/samples/   @googleapis/python-samples-owners @googleapis/actools-python
diff --git a/.github/CONTRIBUTING.md b/.github/CONTRIBUTING.md
new file mode 100644
index 0000000..939e534
--- /dev/null
+++ b/.github/CONTRIBUTING.md
@@ -0,0 +1,28 @@
+# How to Contribute
+
+We'd love to accept your patches and contributions to this project. There are
+just a few small guidelines you need to follow.
+
+## Contributor License Agreement
+
+Contributions to this project must be accompanied by a Contributor License
+Agreement. You (or your employer) retain the copyright to your contribution;
+this simply gives us permission to use and redistribute your contributions as
+part of the project. Head over to <https://cla.developers.google.com/> to see
+your current agreements on file or to sign a new one.
+
+You generally only need to submit a CLA once, so if you've already submitted one
+(even if it was for a different project), you probably don't need to do it
+again.
+
+## Code reviews
+
+All submissions, including submissions by project members, require review. We
+use GitHub pull requests for this purpose. Consult
+[GitHub Help](https://help.github.com/articles/about-pull-requests/) for more
+information on using pull requests.
+
+## Community Guidelines
+
+This project follows [Google's Open Source Community
+Guidelines](https://opensource.google.com/conduct/).
diff --git a/.github/ISSUE_TEMPLATE/bug_report.md b/.github/ISSUE_TEMPLATE/bug_report.md
new file mode 100644
index 0000000..ee19f10
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/bug_report.md
@@ -0,0 +1,43 @@
+---
+name: Bug report
+about: Create a report to help us improve
+
+---
+
+Thanks for stopping by to let us know something could be better!
+
+**PLEASE READ**: If you have a support contract with Google, please create an issue in the [support console](https://cloud.google.com/support/) instead of filing on GitHub. This will ensure a timely response.
+
+Please run down the following list and make sure you've tried the usual "quick fixes":
+
+  - Search the issues already opened: https://github.com/googleapis/python-api-core/issues
+  - Search StackOverflow: https://stackoverflow.com/questions/tagged/google-cloud-platform+python
+
+If you are still having issues, please be sure to include as much information as possible:
+
+#### Environment details
+
+  - OS type and version:
+  - Python version: `python --version`
+  - pip version: `pip --version`
+  - `google-api-core` version: `pip show google-api-core`
+
+#### Steps to reproduce
+
+  1. ?
+  2. ?
+
+#### Code example
+
+```python
+# example
+```
+
+#### Stack trace
+```
+# example
+```
+
+Making sure to follow these steps will guarantee the quickest resolution possible.
+
+Thanks!
diff --git a/.github/ISSUE_TEMPLATE/feature_request.md b/.github/ISSUE_TEMPLATE/feature_request.md
new file mode 100644
index 0000000..6365857
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/feature_request.md
@@ -0,0 +1,18 @@
+---
+name: Feature request
+about: Suggest an idea for this library
+
+---
+
+Thanks for stopping by to let us know something could be better!
+
+**PLEASE READ**: If you have a support contract with Google, please create an issue in the [support console](https://cloud.google.com/support/) instead of filing on GitHub. This will ensure a timely response.
+
+ **Is your feature request related to a problem? Please describe.**
+A clear and concise description of what the problem is. Ex. I'm always frustrated when [...]
+ **Describe the solution you'd like**
+A clear and concise description of what you want to happen.
+ **Describe alternatives you've considered**
+A clear and concise description of any alternative solutions or features you've considered.
+ **Additional context**
+Add any other context or screenshots about the feature request here.
diff --git a/.github/ISSUE_TEMPLATE/support_request.md b/.github/ISSUE_TEMPLATE/support_request.md
new file mode 100644
index 0000000..9958690
--- /dev/null
+++ b/.github/ISSUE_TEMPLATE/support_request.md
@@ -0,0 +1,7 @@
+---
+name: Support request
+about: If you have a support contract with Google, please create an issue in the Google Cloud Support console.
+
+---
+
+**PLEASE READ**: If you have a support contract with Google, please create an issue in the [support console](https://cloud.google.com/support/) instead of filing on GitHub. This will ensure a timely response.
diff --git a/.github/PULL_REQUEST_TEMPLATE.md b/.github/PULL_REQUEST_TEMPLATE.md
new file mode 100644
index 0000000..4ca8093
--- /dev/null
+++ b/.github/PULL_REQUEST_TEMPLATE.md
@@ -0,0 +1,7 @@
+Thank you for opening a Pull Request! Before submitting your PR, there are a few things you can do to make sure it goes smoothly:
+- [ ] Make sure to open an issue as a [bug/issue](https://github.com/googleapis/python-api-core/issues/new/choose) before writing your code!  That way we can discuss the change, evaluate designs, and agree on the general idea
+- [ ] Ensure the tests and linter pass
+- [ ] Code coverage does not decrease (if any source code was changed)
+- [ ] Appropriate docs were updated (if necessary)
+
+Fixes #<issue_number_goes_here> 🦕
diff --git a/.github/header-checker-lint.yml b/.github/header-checker-lint.yml
new file mode 100644
index 0000000..6fe78aa
--- /dev/null
+++ b/.github/header-checker-lint.yml
@@ -0,0 +1,15 @@
+{"allowedCopyrightHolders": ["Google LLC"],
+ "allowedLicenses": ["Apache-2.0", "MIT", "BSD-3"],
+ "ignoreFiles": ["**/requirements.txt", "**/requirements-test.txt", "**/__init__.py", "samples/**/constraints.txt", "samples/**/constraints-test.txt"],
+ "sourceFileExtensions": [
+ 	"ts", 
+ 	"js", 
+ 	"java", 
+ 	"sh", 
+ 	"Dockerfile", 
+ 	"yaml", 
+ 	"py",
+ 	"html",
+ 	"txt"
+ ]
+}
\ No newline at end of file
diff --git a/.github/release-please.yml b/.github/release-please.yml
new file mode 100644
index 0000000..4507ad0
--- /dev/null
+++ b/.github/release-please.yml
@@ -0,0 +1 @@
+releaseType: python
diff --git a/.github/snippet-bot.yml b/.github/snippet-bot.yml
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/.github/snippet-bot.yml
diff --git a/.github/sync-repo-settings.yaml b/.github/sync-repo-settings.yaml
new file mode 100644
index 0000000..e621885
--- /dev/null
+++ b/.github/sync-repo-settings.yaml
@@ -0,0 +1,7 @@
+permissionRules:
+  - team: actools-python
+    permission: admin
+  - team: actools
+    permission: admin
+  - team: yoshi-python
+    permission: push
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..99c3a14
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,64 @@
+*.py[cod]
+*.sw[op]
+
+# C extensions
+*.so
+
+# Packages
+*.egg
+*.egg-info
+dist
+build
+eggs
+.eggs
+parts
+bin
+var
+sdist
+develop-eggs
+.installed.cfg
+lib
+lib64
+__pycache__
+
+# Installer logs
+pip-log.txt
+
+# Unit test / coverage reports
+.coverage
+.nox
+.cache
+.pytest_cache
+.pytype
+
+
+# Mac
+.DS_Store
+
+# JetBrains
+.idea
+
+# VS Code
+.vscode
+
+# emacs
+*~
+
+# Built documentation
+docs/_build
+bigquery/docs/generated
+docs.metadata
+
+# Virtual environment
+env/
+
+# Test logs
+coverage.xml
+*sponge_log.xml
+
+# System test environment variables.
+system_tests/local_test_setup
+
+# Make sure a generated file isn't accidentally committed.
+pylintrc
+pylintrc.test
diff --git a/.kokoro/build.sh b/.kokoro/build.sh
new file mode 100755
index 0000000..0394c8a
--- /dev/null
+++ b/.kokoro/build.sh
@@ -0,0 +1,59 @@
+#!/bin/bash
+# Copyright 2018 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -eo pipefail
+
+if [[ -z "${PROJECT_ROOT:-}" ]]; then
+    PROJECT_ROOT="github/python-api-core"
+fi
+
+cd "${PROJECT_ROOT}"
+
+# Disable buffering, so that the logs stream through.
+export PYTHONUNBUFFERED=1
+
+# Debug: show build environment
+env | grep KOKORO
+
+# Setup service account credentials.
+export GOOGLE_APPLICATION_CREDENTIALS=${KOKORO_GFILE_DIR}/service-account.json
+
+# Setup project id.
+export PROJECT_ID=$(cat "${KOKORO_GFILE_DIR}/project-id.json")
+
+# Remove old nox
+python3 -m pip uninstall --yes --quiet nox-automation
+
+# Install nox
+python3 -m pip install --upgrade --quiet nox
+python3 -m nox --version
+
+# If this is a continuous build, send the test log to the FlakyBot.
+# See https://github.com/googleapis/repo-automation-bots/tree/main/packages/flakybot.
+if [[ $KOKORO_BUILD_ARTIFACTS_SUBDIR = *"continuous"* ]]; then
+  cleanup() {
+    chmod +x $KOKORO_GFILE_DIR/linux_amd64/flakybot
+    $KOKORO_GFILE_DIR/linux_amd64/flakybot
+  }
+  trap cleanup EXIT HUP
+fi
+
+# If NOX_SESSION is set, it only runs the specified session,
+# otherwise run all the sessions.
+if [[ -n "${NOX_SESSION:-}" ]]; then
+    python3 -m nox -s ${NOX_SESSION:-}
+else
+    python3 -m nox
+fi
diff --git a/.kokoro/continuous/common.cfg b/.kokoro/continuous/common.cfg
new file mode 100644
index 0000000..9f2fa73
--- /dev/null
+++ b/.kokoro/continuous/common.cfg
@@ -0,0 +1,27 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+# Download trampoline resources.
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/trampoline"
+
+# Download resources for system tests (service account key, etc.)
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/google-cloud-python"
+
+# Use the trampoline script to run in docker.
+build_file: "python-api-core/.kokoro/trampoline.sh"
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE"
+    value: "gcr.io/cloud-devrel-kokoro-resources/python-multi"
+}
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/build.sh"
+}
diff --git a/.kokoro/continuous/continuous.cfg b/.kokoro/continuous/continuous.cfg
new file mode 100644
index 0000000..8f43917
--- /dev/null
+++ b/.kokoro/continuous/continuous.cfg
@@ -0,0 +1 @@
+# Format: //devtools/kokoro/config/proto/build.proto
\ No newline at end of file
diff --git a/.kokoro/docker/docs/Dockerfile b/.kokoro/docker/docs/Dockerfile
new file mode 100644
index 0000000..4e1b1fb
--- /dev/null
+++ b/.kokoro/docker/docs/Dockerfile
@@ -0,0 +1,67 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from ubuntu:20.04
+
+ENV DEBIAN_FRONTEND noninteractive
+
+# Ensure local Python is preferred over distribution Python.
+ENV PATH /usr/local/bin:$PATH
+
+# Install dependencies.
+RUN apt-get update \
+  && apt-get install -y --no-install-recommends \
+    apt-transport-https \
+    build-essential \
+    ca-certificates \
+    curl \
+    dirmngr \
+    git \
+    gpg-agent \
+    graphviz \
+    libbz2-dev \
+    libdb5.3-dev \
+    libexpat1-dev \
+    libffi-dev \
+    liblzma-dev \
+    libreadline-dev \
+    libsnappy-dev \
+    libssl-dev \
+    libsqlite3-dev \
+    portaudio19-dev \
+    python3-distutils \
+    redis-server \
+    software-properties-common \
+    ssh \
+    sudo \
+    tcl \
+    tcl-dev \
+    tk \
+    tk-dev \
+    uuid-dev \
+    wget \
+    zlib1g-dev \
+  && add-apt-repository universe \
+  && apt-get update \
+  && apt-get -y install jq \
+  && apt-get clean autoclean \
+  && apt-get autoremove -y \
+  && rm -rf /var/lib/apt/lists/* \
+  && rm -f /var/cache/apt/archives/*.deb
+
+RUN wget -O /tmp/get-pip.py 'https://bootstrap.pypa.io/get-pip.py' \
+  && python3.8 /tmp/get-pip.py \
+  && rm /tmp/get-pip.py
+
+CMD ["python3.8"]
diff --git a/.kokoro/docs/common.cfg b/.kokoro/docs/common.cfg
new file mode 100644
index 0000000..48e8985
--- /dev/null
+++ b/.kokoro/docs/common.cfg
@@ -0,0 +1,67 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+# Download trampoline resources.
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/trampoline"
+
+# Use the trampoline script to run in docker.
+build_file: "python-api-core/.kokoro/trampoline_v2.sh"
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE"
+    value: "gcr.io/cloud-devrel-kokoro-resources/python-lib-docs"
+}
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/publish-docs.sh"
+}
+
+env_vars: {
+    key: "STAGING_BUCKET"
+    value: "docs-staging"
+}
+
+env_vars: {
+    key: "V2_STAGING_BUCKET"
+    # Push non-cloud library docs to `docs-staging-v2-staging` instead of the
+    # Cloud RAD bucket `docs-staging-v2`
+    value: "docs-staging-v2-staging"
+}
+
+# It will upload the docker image after successful builds.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE_UPLOAD"
+    value: "true"
+}
+
+# It will always build the docker image.
+env_vars: {
+    key: "TRAMPOLINE_DOCKERFILE"
+    value: ".kokoro/docker/docs/Dockerfile"
+}
+
+# Fetch the token needed for reporting release status to GitHub
+before_action {
+  fetch_keystore {
+    keystore_resource {
+      keystore_config_id: 73713
+      keyname: "yoshi-automation-github-key"
+    }
+  }
+}
+
+before_action {
+  fetch_keystore {
+    keystore_resource {
+      keystore_config_id: 73713
+      keyname: "docuploader_service_account"
+    }
+  }
+}
\ No newline at end of file
diff --git a/.kokoro/docs/docs-presubmit.cfg b/.kokoro/docs/docs-presubmit.cfg
new file mode 100644
index 0000000..d1ed51e
--- /dev/null
+++ b/.kokoro/docs/docs-presubmit.cfg
@@ -0,0 +1,28 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "STAGING_BUCKET"
+    value: "gcloud-python-test"
+}
+
+env_vars: {
+    key: "V2_STAGING_BUCKET"
+    value: "gcloud-python-test"
+}
+
+# We only upload the image in the main `docs` build.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE_UPLOAD"
+    value: "false"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/build.sh"
+}
+
+# Only run this nox session.
+env_vars: {
+    key: "NOX_SESSION"
+    value: "docs docfx"
+}
diff --git a/.kokoro/docs/docs.cfg b/.kokoro/docs/docs.cfg
new file mode 100644
index 0000000..8f43917
--- /dev/null
+++ b/.kokoro/docs/docs.cfg
@@ -0,0 +1 @@
+# Format: //devtools/kokoro/config/proto/build.proto
\ No newline at end of file
diff --git a/.kokoro/populate-secrets.sh b/.kokoro/populate-secrets.sh
new file mode 100755
index 0000000..f525142
--- /dev/null
+++ b/.kokoro/populate-secrets.sh
@@ -0,0 +1,43 @@
+#!/bin/bash
+# Copyright 2020 Google LLC.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -eo pipefail
+
+function now { date +"%Y-%m-%d %H:%M:%S" | tr -d '\n' ;}
+function msg { println "$*" >&2 ;}
+function println { printf '%s\n' "$(now) $*" ;}
+
+
+# Populates requested secrets set in SECRET_MANAGER_KEYS from service account:
+# kokoro-trampoline@cloud-devrel-kokoro-resources.iam.gserviceaccount.com
+SECRET_LOCATION="${KOKORO_GFILE_DIR}/secret_manager"
+msg "Creating folder on disk for secrets: ${SECRET_LOCATION}"
+mkdir -p ${SECRET_LOCATION}
+for key in $(echo ${SECRET_MANAGER_KEYS} | sed "s/,/ /g")
+do
+  msg "Retrieving secret ${key}"
+  docker run --entrypoint=gcloud \
+    --volume=${KOKORO_GFILE_DIR}:${KOKORO_GFILE_DIR} \
+    gcr.io/google.com/cloudsdktool/cloud-sdk \
+    secrets versions access latest \
+    --project cloud-devrel-kokoro-resources \
+    --secret ${key} > \
+    "${SECRET_LOCATION}/${key}"
+  if [[ $? == 0 ]]; then
+    msg "Secret written to ${SECRET_LOCATION}/${key}"
+  else
+    msg "Error retrieving secret ${key}"
+  fi
+done
diff --git a/.kokoro/presubmit/common.cfg b/.kokoro/presubmit/common.cfg
new file mode 100644
index 0000000..9f2fa73
--- /dev/null
+++ b/.kokoro/presubmit/common.cfg
@@ -0,0 +1,27 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+# Download trampoline resources.
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/trampoline"
+
+# Download resources for system tests (service account key, etc.)
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/google-cloud-python"
+
+# Use the trampoline script to run in docker.
+build_file: "python-api-core/.kokoro/trampoline.sh"
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE"
+    value: "gcr.io/cloud-devrel-kokoro-resources/python-multi"
+}
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/build.sh"
+}
diff --git a/.kokoro/presubmit/presubmit.cfg b/.kokoro/presubmit/presubmit.cfg
new file mode 100644
index 0000000..8f43917
--- /dev/null
+++ b/.kokoro/presubmit/presubmit.cfg
@@ -0,0 +1 @@
+# Format: //devtools/kokoro/config/proto/build.proto
\ No newline at end of file
diff --git a/.kokoro/publish-docs.sh b/.kokoro/publish-docs.sh
new file mode 100755
index 0000000..8acb14e
--- /dev/null
+++ b/.kokoro/publish-docs.sh
@@ -0,0 +1,64 @@
+#!/bin/bash
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -eo pipefail
+
+# Disable buffering, so that the logs stream through.
+export PYTHONUNBUFFERED=1
+
+export PATH="${HOME}/.local/bin:${PATH}"
+
+# Install nox
+python3 -m pip install --user --upgrade --quiet nox
+python3 -m nox --version
+
+# build docs
+nox -s docs
+
+python3 -m pip install --user gcp-docuploader
+
+# create metadata
+python3 -m docuploader create-metadata \
+  --name=$(jq --raw-output '.name // empty' .repo-metadata.json) \
+  --version=$(python3 setup.py --version) \
+  --language=$(jq --raw-output '.language // empty' .repo-metadata.json) \
+  --distribution-name=$(python3 setup.py --name) \
+  --product-page=$(jq --raw-output '.product_documentation // empty' .repo-metadata.json) \
+  --github-repository=$(jq --raw-output '.repo // empty' .repo-metadata.json) \
+  --issue-tracker=$(jq --raw-output '.issue_tracker // empty' .repo-metadata.json)
+
+cat docs.metadata
+
+# upload docs
+python3 -m docuploader upload docs/_build/html --metadata-file docs.metadata --staging-bucket "${STAGING_BUCKET}"
+
+
+# docfx yaml files
+nox -s docfx
+
+# create metadata.
+python3 -m docuploader create-metadata \
+  --name=$(jq --raw-output '.name // empty' .repo-metadata.json) \
+  --version=$(python3 setup.py --version) \
+  --language=$(jq --raw-output '.language // empty' .repo-metadata.json) \
+  --distribution-name=$(python3 setup.py --name) \
+  --product-page=$(jq --raw-output '.product_documentation // empty' .repo-metadata.json) \
+  --github-repository=$(jq --raw-output '.repo // empty' .repo-metadata.json) \
+  --issue-tracker=$(jq --raw-output '.issue_tracker // empty' .repo-metadata.json)
+
+cat docs.metadata
+
+# upload docs
+python3 -m docuploader upload docs/_build/html/docfx_yaml --metadata-file docs.metadata --destination-prefix docfx --staging-bucket "${V2_STAGING_BUCKET}"
diff --git a/.kokoro/release.sh b/.kokoro/release.sh
new file mode 100755
index 0000000..0728ce1
--- /dev/null
+++ b/.kokoro/release.sh
@@ -0,0 +1,32 @@
+#!/bin/bash
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -eo pipefail
+
+# Start the releasetool reporter
+python3 -m pip install gcp-releasetool
+python3 -m releasetool publish-reporter-script > /tmp/publisher-script; source /tmp/publisher-script
+
+# Ensure that we have the latest versions of Twine, Wheel, and Setuptools.
+python3 -m pip install --upgrade twine wheel setuptools
+
+# Disable buffering, so that the logs stream through.
+export PYTHONUNBUFFERED=1
+
+# Move into the package, build the distribution and upload.
+TWINE_PASSWORD=$(cat "${KOKORO_GFILE_DIR}/secret_manager/google-cloud-pypi-token")
+cd github/python-api-core
+python3 setup.py sdist bdist_wheel
+twine upload --username __token__ --password "${TWINE_PASSWORD}" dist/*
diff --git a/.kokoro/release/common.cfg b/.kokoro/release/common.cfg
new file mode 100644
index 0000000..586e764
--- /dev/null
+++ b/.kokoro/release/common.cfg
@@ -0,0 +1,30 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+# Download trampoline resources.
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/trampoline"
+
+# Use the trampoline script to run in docker.
+build_file: "python-api-core/.kokoro/trampoline.sh"
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE"
+    value: "gcr.io/cloud-devrel-kokoro-resources/python-multi"
+}
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/release.sh"
+}
+
+# Tokens needed to report release status back to GitHub
+env_vars: {
+  key: "SECRET_MANAGER_KEYS"
+  value: "releasetool-publish-reporter-app,releasetool-publish-reporter-googleapis-installation,releasetool-publish-reporter-pem,google-cloud-pypi-token"
+}
diff --git a/.kokoro/release/release.cfg b/.kokoro/release/release.cfg
new file mode 100644
index 0000000..8f43917
--- /dev/null
+++ b/.kokoro/release/release.cfg
@@ -0,0 +1 @@
+# Format: //devtools/kokoro/config/proto/build.proto
\ No newline at end of file
diff --git a/.kokoro/samples/lint/common.cfg b/.kokoro/samples/lint/common.cfg
new file mode 100644
index 0000000..1a2b87b
--- /dev/null
+++ b/.kokoro/samples/lint/common.cfg
@@ -0,0 +1,34 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+# Specify which tests to run
+env_vars: {
+    key: "RUN_TESTS_SESSION"
+    value: "lint"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/test-samples.sh"
+}
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE"
+    value: "gcr.io/cloud-devrel-kokoro-resources/python-samples-testing-docker"
+}
+
+# Download secrets for samples
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/python-docs-samples"
+
+# Download trampoline resources.
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/trampoline"
+
+# Use the trampoline script to run in docker.
+build_file: "python-api-core/.kokoro/trampoline_v2.sh"
\ No newline at end of file
diff --git a/.kokoro/samples/lint/continuous.cfg b/.kokoro/samples/lint/continuous.cfg
new file mode 100644
index 0000000..a1c8d97
--- /dev/null
+++ b/.kokoro/samples/lint/continuous.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
\ No newline at end of file
diff --git a/.kokoro/samples/lint/periodic.cfg b/.kokoro/samples/lint/periodic.cfg
new file mode 100644
index 0000000..50fec96
--- /dev/null
+++ b/.kokoro/samples/lint/periodic.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "False"
+}
\ No newline at end of file
diff --git a/.kokoro/samples/lint/presubmit.cfg b/.kokoro/samples/lint/presubmit.cfg
new file mode 100644
index 0000000..a1c8d97
--- /dev/null
+++ b/.kokoro/samples/lint/presubmit.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
\ No newline at end of file
diff --git a/.kokoro/samples/python3.10/common.cfg b/.kokoro/samples/python3.10/common.cfg
new file mode 100644
index 0000000..40fb8d8
--- /dev/null
+++ b/.kokoro/samples/python3.10/common.cfg
@@ -0,0 +1,40 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+# Specify which tests to run
+env_vars: {
+    key: "RUN_TESTS_SESSION"
+    value: "py-3.10"
+}
+
+# Declare build specific Cloud project.
+env_vars: {
+    key: "BUILD_SPECIFIC_GCLOUD_PROJECT"
+    value: "python-docs-samples-tests-310"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/test-samples.sh"
+}
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE"
+    value: "gcr.io/cloud-devrel-kokoro-resources/python-samples-testing-docker"
+}
+
+# Download secrets for samples
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/python-docs-samples"
+
+# Download trampoline resources.
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/trampoline"
+
+# Use the trampoline script to run in docker.
+build_file: "python-api-core/.kokoro/trampoline_v2.sh"
\ No newline at end of file
diff --git a/.kokoro/samples/python3.10/continuous.cfg b/.kokoro/samples/python3.10/continuous.cfg
new file mode 100644
index 0000000..a1c8d97
--- /dev/null
+++ b/.kokoro/samples/python3.10/continuous.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
\ No newline at end of file
diff --git a/.kokoro/samples/python3.10/periodic-head.cfg b/.kokoro/samples/python3.10/periodic-head.cfg
new file mode 100644
index 0000000..a18c0cf
--- /dev/null
+++ b/.kokoro/samples/python3.10/periodic-head.cfg
@@ -0,0 +1,11 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/test-samples-against-head.sh"
+}
diff --git a/.kokoro/samples/python3.10/periodic.cfg b/.kokoro/samples/python3.10/periodic.cfg
new file mode 100644
index 0000000..71cd1e5
--- /dev/null
+++ b/.kokoro/samples/python3.10/periodic.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "False"
+}
diff --git a/.kokoro/samples/python3.10/presubmit.cfg b/.kokoro/samples/python3.10/presubmit.cfg
new file mode 100644
index 0000000..a1c8d97
--- /dev/null
+++ b/.kokoro/samples/python3.10/presubmit.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
\ No newline at end of file
diff --git a/.kokoro/samples/python3.6/common.cfg b/.kokoro/samples/python3.6/common.cfg
new file mode 100644
index 0000000..3bb6b3a
--- /dev/null
+++ b/.kokoro/samples/python3.6/common.cfg
@@ -0,0 +1,40 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+# Specify which tests to run
+env_vars: {
+    key: "RUN_TESTS_SESSION"
+    value: "py-3.6"
+}
+
+# Declare build specific Cloud project.
+env_vars: {
+    key: "BUILD_SPECIFIC_GCLOUD_PROJECT"
+    value: "python-docs-samples-tests-py36"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/test-samples.sh"
+}
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE"
+    value: "gcr.io/cloud-devrel-kokoro-resources/python-samples-testing-docker"
+}
+
+# Download secrets for samples
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/python-docs-samples"
+
+# Download trampoline resources.
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/trampoline"
+
+# Use the trampoline script to run in docker.
+build_file: "python-api-core/.kokoro/trampoline_v2.sh"
\ No newline at end of file
diff --git a/.kokoro/samples/python3.6/continuous.cfg b/.kokoro/samples/python3.6/continuous.cfg
new file mode 100644
index 0000000..7218af1
--- /dev/null
+++ b/.kokoro/samples/python3.6/continuous.cfg
@@ -0,0 +1,7 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
+
diff --git a/.kokoro/samples/python3.6/periodic-head.cfg b/.kokoro/samples/python3.6/periodic-head.cfg
new file mode 100644
index 0000000..a18c0cf
--- /dev/null
+++ b/.kokoro/samples/python3.6/periodic-head.cfg
@@ -0,0 +1,11 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/test-samples-against-head.sh"
+}
diff --git a/.kokoro/samples/python3.6/periodic.cfg b/.kokoro/samples/python3.6/periodic.cfg
new file mode 100644
index 0000000..71cd1e5
--- /dev/null
+++ b/.kokoro/samples/python3.6/periodic.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "False"
+}
diff --git a/.kokoro/samples/python3.6/presubmit.cfg b/.kokoro/samples/python3.6/presubmit.cfg
new file mode 100644
index 0000000..a1c8d97
--- /dev/null
+++ b/.kokoro/samples/python3.6/presubmit.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
\ No newline at end of file
diff --git a/.kokoro/samples/python3.7/common.cfg b/.kokoro/samples/python3.7/common.cfg
new file mode 100644
index 0000000..a3aa10b
--- /dev/null
+++ b/.kokoro/samples/python3.7/common.cfg
@@ -0,0 +1,40 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+# Specify which tests to run
+env_vars: {
+    key: "RUN_TESTS_SESSION"
+    value: "py-3.7"
+}
+
+# Declare build specific Cloud project.
+env_vars: {
+    key: "BUILD_SPECIFIC_GCLOUD_PROJECT"
+    value: "python-docs-samples-tests-py37"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/test-samples.sh"
+}
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE"
+    value: "gcr.io/cloud-devrel-kokoro-resources/python-samples-testing-docker"
+}
+
+# Download secrets for samples
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/python-docs-samples"
+
+# Download trampoline resources.
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/trampoline"
+
+# Use the trampoline script to run in docker.
+build_file: "python-api-core/.kokoro/trampoline_v2.sh"
\ No newline at end of file
diff --git a/.kokoro/samples/python3.7/continuous.cfg b/.kokoro/samples/python3.7/continuous.cfg
new file mode 100644
index 0000000..a1c8d97
--- /dev/null
+++ b/.kokoro/samples/python3.7/continuous.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
\ No newline at end of file
diff --git a/.kokoro/samples/python3.7/periodic-head.cfg b/.kokoro/samples/python3.7/periodic-head.cfg
new file mode 100644
index 0000000..a18c0cf
--- /dev/null
+++ b/.kokoro/samples/python3.7/periodic-head.cfg
@@ -0,0 +1,11 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/test-samples-against-head.sh"
+}
diff --git a/.kokoro/samples/python3.7/periodic.cfg b/.kokoro/samples/python3.7/periodic.cfg
new file mode 100644
index 0000000..71cd1e5
--- /dev/null
+++ b/.kokoro/samples/python3.7/periodic.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "False"
+}
diff --git a/.kokoro/samples/python3.7/presubmit.cfg b/.kokoro/samples/python3.7/presubmit.cfg
new file mode 100644
index 0000000..a1c8d97
--- /dev/null
+++ b/.kokoro/samples/python3.7/presubmit.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
\ No newline at end of file
diff --git a/.kokoro/samples/python3.8/common.cfg b/.kokoro/samples/python3.8/common.cfg
new file mode 100644
index 0000000..20c941a
--- /dev/null
+++ b/.kokoro/samples/python3.8/common.cfg
@@ -0,0 +1,40 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+# Specify which tests to run
+env_vars: {
+    key: "RUN_TESTS_SESSION"
+    value: "py-3.8"
+}
+
+# Declare build specific Cloud project.
+env_vars: {
+    key: "BUILD_SPECIFIC_GCLOUD_PROJECT"
+    value: "python-docs-samples-tests-py38"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/test-samples.sh"
+}
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE"
+    value: "gcr.io/cloud-devrel-kokoro-resources/python-samples-testing-docker"
+}
+
+# Download secrets for samples
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/python-docs-samples"
+
+# Download trampoline resources.
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/trampoline"
+
+# Use the trampoline script to run in docker.
+build_file: "python-api-core/.kokoro/trampoline_v2.sh"
\ No newline at end of file
diff --git a/.kokoro/samples/python3.8/continuous.cfg b/.kokoro/samples/python3.8/continuous.cfg
new file mode 100644
index 0000000..a1c8d97
--- /dev/null
+++ b/.kokoro/samples/python3.8/continuous.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
\ No newline at end of file
diff --git a/.kokoro/samples/python3.8/periodic-head.cfg b/.kokoro/samples/python3.8/periodic-head.cfg
new file mode 100644
index 0000000..a18c0cf
--- /dev/null
+++ b/.kokoro/samples/python3.8/periodic-head.cfg
@@ -0,0 +1,11 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/test-samples-against-head.sh"
+}
diff --git a/.kokoro/samples/python3.8/periodic.cfg b/.kokoro/samples/python3.8/periodic.cfg
new file mode 100644
index 0000000..71cd1e5
--- /dev/null
+++ b/.kokoro/samples/python3.8/periodic.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "False"
+}
diff --git a/.kokoro/samples/python3.8/presubmit.cfg b/.kokoro/samples/python3.8/presubmit.cfg
new file mode 100644
index 0000000..a1c8d97
--- /dev/null
+++ b/.kokoro/samples/python3.8/presubmit.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
\ No newline at end of file
diff --git a/.kokoro/samples/python3.9/common.cfg b/.kokoro/samples/python3.9/common.cfg
new file mode 100644
index 0000000..234887c
--- /dev/null
+++ b/.kokoro/samples/python3.9/common.cfg
@@ -0,0 +1,40 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+# Build logs will be here
+action {
+  define_artifacts {
+    regex: "**/*sponge_log.xml"
+  }
+}
+
+# Specify which tests to run
+env_vars: {
+    key: "RUN_TESTS_SESSION"
+    value: "py-3.9"
+}
+
+# Declare build specific Cloud project.
+env_vars: {
+    key: "BUILD_SPECIFIC_GCLOUD_PROJECT"
+    value: "python-docs-samples-tests-py39"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/test-samples.sh"
+}
+
+# Configure the docker image for kokoro-trampoline.
+env_vars: {
+    key: "TRAMPOLINE_IMAGE"
+    value: "gcr.io/cloud-devrel-kokoro-resources/python-samples-testing-docker"
+}
+
+# Download secrets for samples
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/python-docs-samples"
+
+# Download trampoline resources.
+gfile_resources: "/bigstore/cloud-devrel-kokoro-resources/trampoline"
+
+# Use the trampoline script to run in docker.
+build_file: "python-api-core/.kokoro/trampoline_v2.sh"
\ No newline at end of file
diff --git a/.kokoro/samples/python3.9/continuous.cfg b/.kokoro/samples/python3.9/continuous.cfg
new file mode 100644
index 0000000..a1c8d97
--- /dev/null
+++ b/.kokoro/samples/python3.9/continuous.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
\ No newline at end of file
diff --git a/.kokoro/samples/python3.9/periodic-head.cfg b/.kokoro/samples/python3.9/periodic-head.cfg
new file mode 100644
index 0000000..a18c0cf
--- /dev/null
+++ b/.kokoro/samples/python3.9/periodic-head.cfg
@@ -0,0 +1,11 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: "github/python-api-core/.kokoro/test-samples-against-head.sh"
+}
diff --git a/.kokoro/samples/python3.9/periodic.cfg b/.kokoro/samples/python3.9/periodic.cfg
new file mode 100644
index 0000000..71cd1e5
--- /dev/null
+++ b/.kokoro/samples/python3.9/periodic.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "False"
+}
diff --git a/.kokoro/samples/python3.9/presubmit.cfg b/.kokoro/samples/python3.9/presubmit.cfg
new file mode 100644
index 0000000..a1c8d97
--- /dev/null
+++ b/.kokoro/samples/python3.9/presubmit.cfg
@@ -0,0 +1,6 @@
+# Format: //devtools/kokoro/config/proto/build.proto
+
+env_vars: {
+    key: "INSTALL_LIBRARY_FROM_SOURCE"
+    value: "True"
+}
\ No newline at end of file
diff --git a/.kokoro/test-samples-against-head.sh b/.kokoro/test-samples-against-head.sh
new file mode 100755
index 0000000..ba3a707
--- /dev/null
+++ b/.kokoro/test-samples-against-head.sh
@@ -0,0 +1,26 @@
+#!/bin/bash
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# A customized test runner for samples.
+#
+# For periodic builds, you can specify this file for testing against head.
+
+# `-e` enables the script to automatically fail when a command fails
+# `-o pipefail` sets the exit code to the rightmost comment to exit with a non-zero
+set -eo pipefail
+# Enables `**` to include files nested inside sub-folders
+shopt -s globstar
+
+exec .kokoro/test-samples-impl.sh
diff --git a/.kokoro/test-samples-impl.sh b/.kokoro/test-samples-impl.sh
new file mode 100755
index 0000000..8a324c9
--- /dev/null
+++ b/.kokoro/test-samples-impl.sh
@@ -0,0 +1,102 @@
+#!/bin/bash
+# Copyright 2021 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+# `-e` enables the script to automatically fail when a command fails
+# `-o pipefail` sets the exit code to the rightmost comment to exit with a non-zero
+set -eo pipefail
+# Enables `**` to include files nested inside sub-folders
+shopt -s globstar
+
+# Exit early if samples don't exist
+if ! find samples -name 'requirements.txt' | grep -q .; then
+  echo "No tests run. './samples/**/requirements.txt' not found"
+  exit 0
+fi
+
+# Disable buffering, so that the logs stream through.
+export PYTHONUNBUFFERED=1
+
+# Debug: show build environment
+env | grep KOKORO
+
+# Install nox
+python3.6 -m pip install --upgrade --quiet nox
+
+# Use secrets acessor service account to get secrets
+if [[ -f "${KOKORO_GFILE_DIR}/secrets_viewer_service_account.json" ]]; then
+    gcloud auth activate-service-account \
+	   --key-file="${KOKORO_GFILE_DIR}/secrets_viewer_service_account.json" \
+	   --project="cloud-devrel-kokoro-resources"
+fi
+
+# This script will create 3 files:
+# - testing/test-env.sh
+# - testing/service-account.json
+# - testing/client-secrets.json
+./scripts/decrypt-secrets.sh
+
+source ./testing/test-env.sh
+export GOOGLE_APPLICATION_CREDENTIALS=$(pwd)/testing/service-account.json
+
+# For cloud-run session, we activate the service account for gcloud sdk.
+gcloud auth activate-service-account \
+       --key-file "${GOOGLE_APPLICATION_CREDENTIALS}"
+
+export GOOGLE_CLIENT_SECRETS=$(pwd)/testing/client-secrets.json
+
+echo -e "\n******************** TESTING PROJECTS ********************"
+
+# Switch to 'fail at end' to allow all tests to complete before exiting.
+set +e
+# Use RTN to return a non-zero value if the test fails.
+RTN=0
+ROOT=$(pwd)
+# Find all requirements.txt in the samples directory (may break on whitespace).
+for file in samples/**/requirements.txt; do
+    cd "$ROOT"
+    # Navigate to the project folder.
+    file=$(dirname "$file")
+    cd "$file"
+
+    echo "------------------------------------------------------------"
+    echo "- testing $file"
+    echo "------------------------------------------------------------"
+
+    # Use nox to execute the tests for the project.
+    python3.6 -m nox -s "$RUN_TESTS_SESSION"
+    EXIT=$?
+
+    # If this is a periodic build, send the test log to the FlakyBot.
+    # See https://github.com/googleapis/repo-automation-bots/tree/main/packages/flakybot.
+    if [[ $KOKORO_BUILD_ARTIFACTS_SUBDIR = *"periodic"* ]]; then
+      chmod +x $KOKORO_GFILE_DIR/linux_amd64/flakybot
+      $KOKORO_GFILE_DIR/linux_amd64/flakybot
+    fi
+
+    if [[ $EXIT -ne 0 ]]; then
+      RTN=1
+      echo -e "\n Testing failed: Nox returned a non-zero exit code. \n"
+    else
+      echo -e "\n Testing completed.\n"
+    fi
+
+done
+cd "$ROOT"
+
+# Workaround for Kokoro permissions issue: delete secrets
+rm testing/{test-env.sh,client-secrets.json,service-account.json}
+
+exit "$RTN"
diff --git a/.kokoro/test-samples.sh b/.kokoro/test-samples.sh
new file mode 100755
index 0000000..11c042d
--- /dev/null
+++ b/.kokoro/test-samples.sh
@@ -0,0 +1,44 @@
+#!/bin/bash
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# The default test runner for samples.
+#
+# For periodic builds, we rewinds the repo to the latest release, and
+# run test-samples-impl.sh.
+
+# `-e` enables the script to automatically fail when a command fails
+# `-o pipefail` sets the exit code to the rightmost comment to exit with a non-zero
+set -eo pipefail
+# Enables `**` to include files nested inside sub-folders
+shopt -s globstar
+
+# Run periodic samples tests at latest release
+if [[ $KOKORO_BUILD_ARTIFACTS_SUBDIR = *"periodic"* ]]; then
+    # preserving the test runner implementation.
+    cp .kokoro/test-samples-impl.sh "${TMPDIR}/test-samples-impl.sh"
+    echo "--- IMPORTANT IMPORTANT IMPORTANT ---"
+    echo "Now we rewind the repo back to the latest release..."
+    LATEST_RELEASE=$(git describe --abbrev=0 --tags)
+    git checkout $LATEST_RELEASE
+    echo "The current head is: "
+    echo $(git rev-parse --verify HEAD)
+    echo "--- IMPORTANT IMPORTANT IMPORTANT ---"
+    # move back the test runner implementation if there's no file.
+    if [ ! -f .kokoro/test-samples-impl.sh ]; then
+	cp "${TMPDIR}/test-samples-impl.sh" .kokoro/test-samples-impl.sh
+    fi
+fi
+
+exec .kokoro/test-samples-impl.sh
diff --git a/.kokoro/trampoline.sh b/.kokoro/trampoline.sh
new file mode 100755
index 0000000..f39236e
--- /dev/null
+++ b/.kokoro/trampoline.sh
@@ -0,0 +1,28 @@
+#!/bin/bash
+# Copyright 2017 Google Inc.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+set -eo pipefail
+
+# Always run the cleanup script, regardless of the success of bouncing into
+# the container.
+function cleanup() {
+    chmod +x ${KOKORO_GFILE_DIR}/trampoline_cleanup.sh
+    ${KOKORO_GFILE_DIR}/trampoline_cleanup.sh
+    echo "cleanup";
+}
+trap cleanup EXIT
+
+$(dirname $0)/populate-secrets.sh # Secret Manager secrets.
+python3 "${KOKORO_GFILE_DIR}/trampoline_v1.py"
\ No newline at end of file
diff --git a/.kokoro/trampoline_v2.sh b/.kokoro/trampoline_v2.sh
new file mode 100755
index 0000000..4af6cdc
--- /dev/null
+++ b/.kokoro/trampoline_v2.sh
@@ -0,0 +1,487 @@
+#!/usr/bin/env bash
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# trampoline_v2.sh
+#
+# This script does 3 things.
+#
+# 1. Prepare the Docker image for the test
+# 2. Run the Docker with appropriate flags to run the test
+# 3. Upload the newly built Docker image
+#
+# in a way that is somewhat compatible with trampoline_v1.
+#
+# To run this script, first download few files from gcs to /dev/shm.
+# (/dev/shm is passed into the container as KOKORO_GFILE_DIR).
+#
+# gsutil cp gs://cloud-devrel-kokoro-resources/python-docs-samples/secrets_viewer_service_account.json /dev/shm
+# gsutil cp gs://cloud-devrel-kokoro-resources/python-docs-samples/automl_secrets.txt /dev/shm
+#
+# Then run the script.
+# .kokoro/trampoline_v2.sh
+#
+# These environment variables are required:
+# TRAMPOLINE_IMAGE: The docker image to use.
+# TRAMPOLINE_DOCKERFILE: The location of the Dockerfile.
+#
+# You can optionally change these environment variables:
+# TRAMPOLINE_IMAGE_UPLOAD:
+#     (true|false): Whether to upload the Docker image after the
+#                   successful builds.
+# TRAMPOLINE_BUILD_FILE: The script to run in the docker container.
+# TRAMPOLINE_WORKSPACE: The workspace path in the docker container.
+#                       Defaults to /workspace.
+# Potentially there are some repo specific envvars in .trampolinerc in
+# the project root.
+
+
+set -euo pipefail
+
+TRAMPOLINE_VERSION="2.0.5"
+
+if command -v tput >/dev/null && [[ -n "${TERM:-}" ]]; then
+  readonly IO_COLOR_RED="$(tput setaf 1)"
+  readonly IO_COLOR_GREEN="$(tput setaf 2)"
+  readonly IO_COLOR_YELLOW="$(tput setaf 3)"
+  readonly IO_COLOR_RESET="$(tput sgr0)"
+else
+  readonly IO_COLOR_RED=""
+  readonly IO_COLOR_GREEN=""
+  readonly IO_COLOR_YELLOW=""
+  readonly IO_COLOR_RESET=""
+fi
+
+function function_exists {
+    [ $(LC_ALL=C type -t $1)"" == "function" ]
+}
+
+# Logs a message using the given color. The first argument must be one
+# of the IO_COLOR_* variables defined above, such as
+# "${IO_COLOR_YELLOW}". The remaining arguments will be logged in the
+# given color. The log message will also have an RFC-3339 timestamp
+# prepended (in UTC). You can disable the color output by setting
+# TERM=vt100.
+function log_impl() {
+    local color="$1"
+    shift
+    local timestamp="$(date -u "+%Y-%m-%dT%H:%M:%SZ")"
+    echo "================================================================"
+    echo "${color}${timestamp}:" "$@" "${IO_COLOR_RESET}"
+    echo "================================================================"
+}
+
+# Logs the given message with normal coloring and a timestamp.
+function log() {
+  log_impl "${IO_COLOR_RESET}" "$@"
+}
+
+# Logs the given message in green with a timestamp.
+function log_green() {
+  log_impl "${IO_COLOR_GREEN}" "$@"
+}
+
+# Logs the given message in yellow with a timestamp.
+function log_yellow() {
+  log_impl "${IO_COLOR_YELLOW}" "$@"
+}
+
+# Logs the given message in red with a timestamp.
+function log_red() {
+  log_impl "${IO_COLOR_RED}" "$@"
+}
+
+readonly tmpdir=$(mktemp -d -t ci-XXXXXXXX)
+readonly tmphome="${tmpdir}/h"
+mkdir -p "${tmphome}"
+
+function cleanup() {
+    rm -rf "${tmpdir}"
+}
+trap cleanup EXIT
+
+RUNNING_IN_CI="${RUNNING_IN_CI:-false}"
+
+# The workspace in the container, defaults to /workspace.
+TRAMPOLINE_WORKSPACE="${TRAMPOLINE_WORKSPACE:-/workspace}"
+
+pass_down_envvars=(
+    # TRAMPOLINE_V2 variables.
+    # Tells scripts whether they are running as part of CI or not.
+    "RUNNING_IN_CI"
+    # Indicates which CI system we're in.
+    "TRAMPOLINE_CI"
+    # Indicates the version of the script.
+    "TRAMPOLINE_VERSION"
+)
+
+log_yellow "Building with Trampoline ${TRAMPOLINE_VERSION}"
+
+# Detect which CI systems we're in. If we're in any of the CI systems
+# we support, `RUNNING_IN_CI` will be true and `TRAMPOLINE_CI` will be
+# the name of the CI system. Both envvars will be passing down to the
+# container for telling which CI system we're in.
+if [[ -n "${KOKORO_BUILD_ID:-}" ]]; then
+    # descriptive env var for indicating it's on CI.
+    RUNNING_IN_CI="true"
+    TRAMPOLINE_CI="kokoro"
+    if [[ "${TRAMPOLINE_USE_LEGACY_SERVICE_ACCOUNT:-}" == "true" ]]; then
+	if [[ ! -f "${KOKORO_GFILE_DIR}/kokoro-trampoline.service-account.json" ]]; then
+	    log_red "${KOKORO_GFILE_DIR}/kokoro-trampoline.service-account.json does not exist. Did you forget to mount cloud-devrel-kokoro-resources/trampoline? Aborting."
+	    exit 1
+	fi
+	# This service account will be activated later.
+	TRAMPOLINE_SERVICE_ACCOUNT="${KOKORO_GFILE_DIR}/kokoro-trampoline.service-account.json"
+    else
+	if [[ "${TRAMPOLINE_VERBOSE:-}" == "true" ]]; then
+	    gcloud auth list
+	fi
+	log_yellow "Configuring Container Registry access"
+	gcloud auth configure-docker --quiet
+    fi
+    pass_down_envvars+=(
+	# KOKORO dynamic variables.
+	"KOKORO_BUILD_NUMBER"
+	"KOKORO_BUILD_ID"
+	"KOKORO_JOB_NAME"
+	"KOKORO_GIT_COMMIT"
+	"KOKORO_GITHUB_COMMIT"
+	"KOKORO_GITHUB_PULL_REQUEST_NUMBER"
+	"KOKORO_GITHUB_PULL_REQUEST_COMMIT"
+	# For FlakyBot
+	"KOKORO_GITHUB_COMMIT_URL"
+	"KOKORO_GITHUB_PULL_REQUEST_URL"
+    )
+elif [[ "${TRAVIS:-}" == "true" ]]; then
+    RUNNING_IN_CI="true"
+    TRAMPOLINE_CI="travis"
+    pass_down_envvars+=(
+	"TRAVIS_BRANCH"
+	"TRAVIS_BUILD_ID"
+	"TRAVIS_BUILD_NUMBER"
+	"TRAVIS_BUILD_WEB_URL"
+	"TRAVIS_COMMIT"
+	"TRAVIS_COMMIT_MESSAGE"
+	"TRAVIS_COMMIT_RANGE"
+	"TRAVIS_JOB_NAME"
+	"TRAVIS_JOB_NUMBER"
+	"TRAVIS_JOB_WEB_URL"
+	"TRAVIS_PULL_REQUEST"
+	"TRAVIS_PULL_REQUEST_BRANCH"
+	"TRAVIS_PULL_REQUEST_SHA"
+	"TRAVIS_PULL_REQUEST_SLUG"
+	"TRAVIS_REPO_SLUG"
+	"TRAVIS_SECURE_ENV_VARS"
+	"TRAVIS_TAG"
+    )
+elif [[ -n "${GITHUB_RUN_ID:-}" ]]; then
+    RUNNING_IN_CI="true"
+    TRAMPOLINE_CI="github-workflow"
+    pass_down_envvars+=(
+	"GITHUB_WORKFLOW"
+	"GITHUB_RUN_ID"
+	"GITHUB_RUN_NUMBER"
+	"GITHUB_ACTION"
+	"GITHUB_ACTIONS"
+	"GITHUB_ACTOR"
+	"GITHUB_REPOSITORY"
+	"GITHUB_EVENT_NAME"
+	"GITHUB_EVENT_PATH"
+	"GITHUB_SHA"
+	"GITHUB_REF"
+	"GITHUB_HEAD_REF"
+	"GITHUB_BASE_REF"
+    )
+elif [[ "${CIRCLECI:-}" == "true" ]]; then
+    RUNNING_IN_CI="true"
+    TRAMPOLINE_CI="circleci"
+    pass_down_envvars+=(
+	"CIRCLE_BRANCH"
+	"CIRCLE_BUILD_NUM"
+	"CIRCLE_BUILD_URL"
+	"CIRCLE_COMPARE_URL"
+	"CIRCLE_JOB"
+	"CIRCLE_NODE_INDEX"
+	"CIRCLE_NODE_TOTAL"
+	"CIRCLE_PREVIOUS_BUILD_NUM"
+	"CIRCLE_PROJECT_REPONAME"
+	"CIRCLE_PROJECT_USERNAME"
+	"CIRCLE_REPOSITORY_URL"
+	"CIRCLE_SHA1"
+	"CIRCLE_STAGE"
+	"CIRCLE_USERNAME"
+	"CIRCLE_WORKFLOW_ID"
+	"CIRCLE_WORKFLOW_JOB_ID"
+	"CIRCLE_WORKFLOW_UPSTREAM_JOB_IDS"
+	"CIRCLE_WORKFLOW_WORKSPACE_ID"
+    )
+fi
+
+# Configure the service account for pulling the docker image.
+function repo_root() {
+    local dir="$1"
+    while [[ ! -d "${dir}/.git" ]]; do
+	dir="$(dirname "$dir")"
+    done
+    echo "${dir}"
+}
+
+# Detect the project root. In CI builds, we assume the script is in
+# the git tree and traverse from there, otherwise, traverse from `pwd`
+# to find `.git` directory.
+if [[ "${RUNNING_IN_CI:-}" == "true" ]]; then
+    PROGRAM_PATH="$(realpath "$0")"
+    PROGRAM_DIR="$(dirname "${PROGRAM_PATH}")"
+    PROJECT_ROOT="$(repo_root "${PROGRAM_DIR}")"
+else
+    PROJECT_ROOT="$(repo_root $(pwd))"
+fi
+
+log_yellow "Changing to the project root: ${PROJECT_ROOT}."
+cd "${PROJECT_ROOT}"
+
+# To support relative path for `TRAMPOLINE_SERVICE_ACCOUNT`, we need
+# to use this environment variable in `PROJECT_ROOT`.
+if [[ -n "${TRAMPOLINE_SERVICE_ACCOUNT:-}" ]]; then
+
+    mkdir -p "${tmpdir}/gcloud"
+    gcloud_config_dir="${tmpdir}/gcloud"
+
+    log_yellow "Using isolated gcloud config: ${gcloud_config_dir}."
+    export CLOUDSDK_CONFIG="${gcloud_config_dir}"
+
+    log_yellow "Using ${TRAMPOLINE_SERVICE_ACCOUNT} for authentication."
+    gcloud auth activate-service-account \
+	   --key-file "${TRAMPOLINE_SERVICE_ACCOUNT}"
+    log_yellow "Configuring Container Registry access"
+    gcloud auth configure-docker --quiet
+fi
+
+required_envvars=(
+    # The basic trampoline configurations.
+    "TRAMPOLINE_IMAGE"
+    "TRAMPOLINE_BUILD_FILE"
+)
+
+if [[ -f "${PROJECT_ROOT}/.trampolinerc" ]]; then
+    source "${PROJECT_ROOT}/.trampolinerc"
+fi
+
+log_yellow "Checking environment variables."
+for e in "${required_envvars[@]}"
+do
+    if [[ -z "${!e:-}" ]]; then
+	log "Missing ${e} env var. Aborting."
+	exit 1
+    fi
+done
+
+# We want to support legacy style TRAMPOLINE_BUILD_FILE used with V1
+# script: e.g. "github/repo-name/.kokoro/run_tests.sh"
+TRAMPOLINE_BUILD_FILE="${TRAMPOLINE_BUILD_FILE#github/*/}"
+log_yellow "Using TRAMPOLINE_BUILD_FILE: ${TRAMPOLINE_BUILD_FILE}"
+
+# ignore error on docker operations and test execution
+set +e
+
+log_yellow "Preparing Docker image."
+# We only download the docker image in CI builds.
+if [[ "${RUNNING_IN_CI:-}" == "true" ]]; then
+    # Download the docker image specified by `TRAMPOLINE_IMAGE`
+
+    # We may want to add --max-concurrent-downloads flag.
+
+    log_yellow "Start pulling the Docker image: ${TRAMPOLINE_IMAGE}."
+    if docker pull "${TRAMPOLINE_IMAGE}"; then
+	log_green "Finished pulling the Docker image: ${TRAMPOLINE_IMAGE}."
+	has_image="true"
+    else
+	log_red "Failed pulling the Docker image: ${TRAMPOLINE_IMAGE}."
+	has_image="false"
+    fi
+else
+    # For local run, check if we have the image.
+    if docker images "${TRAMPOLINE_IMAGE}:latest" | grep "${TRAMPOLINE_IMAGE}"; then
+	has_image="true"
+    else
+	has_image="false"
+    fi
+fi
+
+
+# The default user for a Docker container has uid 0 (root). To avoid
+# creating root-owned files in the build directory we tell docker to
+# use the current user ID.
+user_uid="$(id -u)"
+user_gid="$(id -g)"
+user_name="$(id -un)"
+
+# To allow docker in docker, we add the user to the docker group in
+# the host os.
+docker_gid=$(cut -d: -f3 < <(getent group docker))
+
+update_cache="false"
+if [[ "${TRAMPOLINE_DOCKERFILE:-none}" != "none" ]]; then
+    # Build the Docker image from the source.
+    context_dir=$(dirname "${TRAMPOLINE_DOCKERFILE}")
+    docker_build_flags=(
+	"-f" "${TRAMPOLINE_DOCKERFILE}"
+	"-t" "${TRAMPOLINE_IMAGE}"
+	"--build-arg" "UID=${user_uid}"
+	"--build-arg" "USERNAME=${user_name}"
+    )
+    if [[ "${has_image}" == "true" ]]; then
+	docker_build_flags+=("--cache-from" "${TRAMPOLINE_IMAGE}")
+    fi
+
+    log_yellow "Start building the docker image."
+    if [[ "${TRAMPOLINE_VERBOSE:-false}" == "true" ]]; then
+	echo "docker build" "${docker_build_flags[@]}" "${context_dir}"
+    fi
+
+    # ON CI systems, we want to suppress docker build logs, only
+    # output the logs when it fails.
+    if [[ "${RUNNING_IN_CI:-}" == "true" ]]; then
+	if docker build "${docker_build_flags[@]}" "${context_dir}" \
+		  > "${tmpdir}/docker_build.log" 2>&1; then
+	    if [[ "${TRAMPOLINE_VERBOSE:-}" == "true" ]]; then
+		cat "${tmpdir}/docker_build.log"
+	    fi
+
+	    log_green "Finished building the docker image."
+	    update_cache="true"
+	else
+	    log_red "Failed to build the Docker image, aborting."
+	    log_yellow "Dumping the build logs:"
+	    cat "${tmpdir}/docker_build.log"
+	    exit 1
+	fi
+    else
+	if docker build "${docker_build_flags[@]}" "${context_dir}"; then
+	    log_green "Finished building the docker image."
+	    update_cache="true"
+	else
+	    log_red "Failed to build the Docker image, aborting."
+	    exit 1
+	fi
+    fi
+else
+    if [[ "${has_image}" != "true" ]]; then
+	log_red "We do not have ${TRAMPOLINE_IMAGE} locally, aborting."
+	exit 1
+    fi
+fi
+
+# We use an array for the flags so they are easier to document.
+docker_flags=(
+    # Remove the container after it exists.
+    "--rm"
+
+    # Use the host network.
+    "--network=host"
+
+    # Run in priviledged mode. We are not using docker for sandboxing or
+    # isolation, just for packaging our dev tools.
+    "--privileged"
+
+    # Run the docker script with the user id. Because the docker image gets to
+    # write in ${PWD} you typically want this to be your user id.
+    # To allow docker in docker, we need to use docker gid on the host.
+    "--user" "${user_uid}:${docker_gid}"
+
+    # Pass down the USER.
+    "--env" "USER=${user_name}"
+
+    # Mount the project directory inside the Docker container.
+    "--volume" "${PROJECT_ROOT}:${TRAMPOLINE_WORKSPACE}"
+    "--workdir" "${TRAMPOLINE_WORKSPACE}"
+    "--env" "PROJECT_ROOT=${TRAMPOLINE_WORKSPACE}"
+
+    # Mount the temporary home directory.
+    "--volume" "${tmphome}:/h"
+    "--env" "HOME=/h"
+
+    # Allow docker in docker.
+    "--volume" "/var/run/docker.sock:/var/run/docker.sock"
+
+    # Mount the /tmp so that docker in docker can mount the files
+    # there correctly.
+    "--volume" "/tmp:/tmp"
+    # Pass down the KOKORO_GFILE_DIR and KOKORO_KEYSTORE_DIR
+    # TODO(tmatsuo): This part is not portable.
+    "--env" "TRAMPOLINE_SECRET_DIR=/secrets"
+    "--volume" "${KOKORO_GFILE_DIR:-/dev/shm}:/secrets/gfile"
+    "--env" "KOKORO_GFILE_DIR=/secrets/gfile"
+    "--volume" "${KOKORO_KEYSTORE_DIR:-/dev/shm}:/secrets/keystore"
+    "--env" "KOKORO_KEYSTORE_DIR=/secrets/keystore"
+)
+
+# Add an option for nicer output if the build gets a tty.
+if [[ -t 0 ]]; then
+    docker_flags+=("-it")
+fi
+
+# Passing down env vars
+for e in "${pass_down_envvars[@]}"
+do
+    if [[ -n "${!e:-}" ]]; then
+	docker_flags+=("--env" "${e}=${!e}")
+    fi
+done
+
+# If arguments are given, all arguments will become the commands run
+# in the container, otherwise run TRAMPOLINE_BUILD_FILE.
+if [[ $# -ge 1 ]]; then
+    log_yellow "Running the given commands '" "${@:1}" "' in the container."
+    readonly commands=("${@:1}")
+    if [[ "${TRAMPOLINE_VERBOSE:-}" == "true" ]]; then
+	echo docker run "${docker_flags[@]}" "${TRAMPOLINE_IMAGE}" "${commands[@]}"
+    fi
+    docker run "${docker_flags[@]}" "${TRAMPOLINE_IMAGE}" "${commands[@]}"
+else
+    log_yellow "Running the tests in a Docker container."
+    docker_flags+=("--entrypoint=${TRAMPOLINE_BUILD_FILE}")
+    if [[ "${TRAMPOLINE_VERBOSE:-}" == "true" ]]; then
+	echo docker run "${docker_flags[@]}" "${TRAMPOLINE_IMAGE}"
+    fi
+    docker run "${docker_flags[@]}" "${TRAMPOLINE_IMAGE}"
+fi
+
+
+test_retval=$?
+
+if [[ ${test_retval} -eq 0 ]]; then
+    log_green "Build finished with ${test_retval}"
+else
+    log_red "Build finished with ${test_retval}"
+fi
+
+# Only upload it when the test passes.
+if [[ "${update_cache}" == "true" ]] && \
+       [[ $test_retval == 0 ]] && \
+       [[ "${TRAMPOLINE_IMAGE_UPLOAD:-false}" == "true" ]]; then
+    log_yellow "Uploading the Docker image."
+    if docker push "${TRAMPOLINE_IMAGE}"; then
+	log_green "Finished uploading the Docker image."
+    else
+	log_red "Failed uploading the Docker image."
+    fi
+    # Call trampoline_after_upload_hook if it's defined.
+    if function_exists trampoline_after_upload_hook; then
+	trampoline_after_upload_hook
+    fi
+
+fi
+
+exit "${test_retval}"
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
new file mode 100644
index 0000000..62eb5a7
--- /dev/null
+++ b/.pre-commit-config.yaml
@@ -0,0 +1,31 @@
+# Copyright 2021 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# See https://pre-commit.com for more information
+# See https://pre-commit.com/hooks.html for more hooks
+repos:
+-   repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v4.0.1
+    hooks:
+    -   id: trailing-whitespace
+    -   id: end-of-file-fixer
+    -   id: check-yaml
+-   repo: https://github.com/psf/black
+    rev: 19.10b0
+    hooks:
+    - id: black
+-   repo: https://gitlab.com/pycqa/flake8
+    rev: 3.9.2
+    hooks:
+    - id: flake8
diff --git a/.repo-metadata.json b/.repo-metadata.json
new file mode 100644
index 0000000..e16c9d2
--- /dev/null
+++ b/.repo-metadata.json
@@ -0,0 +1,12 @@
+{
+    "name": "google-api-core",
+    "name_pretty": "Google API client core library",
+    "client_documentation": "https://googleapis.dev/python/google-api-core/latest",
+    "release_level": "ga",
+    "language": "python",
+    "library_type": "CORE",
+    "repo": "googleapis/python-api-core",
+    "distribution_name": "google-api-core",
+    "default_version": "",
+    "codeowner_team": "@googleapis/actools-python"
+}
diff --git a/.trampolinerc b/.trampolinerc
new file mode 100644
index 0000000..0eee72a
--- /dev/null
+++ b/.trampolinerc
@@ -0,0 +1,63 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Template for .trampolinerc
+
+# Add required env vars here.
+required_envvars+=(
+)
+
+# Add env vars which are passed down into the container here.
+pass_down_envvars+=(
+    "NOX_SESSION"
+    ###############
+    # Docs builds
+    ###############
+    "STAGING_BUCKET"
+    "V2_STAGING_BUCKET"
+    ##################
+    # Samples builds
+    ##################
+    "INSTALL_LIBRARY_FROM_SOURCE"
+    "RUN_TESTS_SESSION"
+    "BUILD_SPECIFIC_GCLOUD_PROJECT"
+    # Target directories.
+    "RUN_TESTS_DIRS"
+    # The nox session to run.
+    "RUN_TESTS_SESSION"
+)
+
+# Prevent unintentional override on the default image.
+if [[ "${TRAMPOLINE_IMAGE_UPLOAD:-false}" == "true" ]] && \
+   [[ -z "${TRAMPOLINE_IMAGE:-}" ]]; then
+   echo "Please set TRAMPOLINE_IMAGE if you want to upload the Docker image."
+   exit 1
+fi
+
+# Define the default value if it makes sense.
+if [[ -z "${TRAMPOLINE_IMAGE_UPLOAD:-}" ]]; then
+    TRAMPOLINE_IMAGE_UPLOAD=""
+fi
+
+if [[ -z "${TRAMPOLINE_IMAGE:-}" ]]; then
+    TRAMPOLINE_IMAGE=""
+fi
+
+if [[ -z "${TRAMPOLINE_DOCKERFILE:-}" ]]; then
+    TRAMPOLINE_DOCKERFILE=""
+fi
+
+if [[ -z "${TRAMPOLINE_BUILD_FILE:-}" ]]; then
+    TRAMPOLINE_BUILD_FILE=""
+fi
diff --git a/Android.bp b/Android.bp
new file mode 100644
index 0000000..b821a42
--- /dev/null
+++ b/Android.bp
@@ -0,0 +1,33 @@
+// Copyright 2022 Google Inc. All rights reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+python_library {
+    name: "py-python-api-core",
+    host_supported: true,
+    srcs: [
+        "google/api_core/future/*.py",
+        "google/api_core/gapic_v1/*.py",
+        "google/api_core/operations_v1/*.py",
+        "google/api_core/operations_v1/transports/*.py",
+        "google/api_core/*.py",
+    ],
+    version: {
+        py2: {
+            enabled: true,
+        },
+        py3: {
+            enabled: true,
+        },
+    },
+}
diff --git a/CHANGELOG.md b/CHANGELOG.md
new file mode 100644
index 0000000..04d47da
--- /dev/null
+++ b/CHANGELOG.md
@@ -0,0 +1,726 @@
+# Changelog
+
+[PyPI History][1]
+
+[1]: https://pypi.org/project/google-api-core/#history
+
+## [2.3.0](https://www.github.com/googleapis/python-api-core/compare/v2.2.2...v2.3.0) (2021-11-25)
+
+
+### Features
+
+* add operations rest client to support long-running operations. ([#311](https://www.github.com/googleapis/python-api-core/issues/311)) ([ce1adf3](https://www.github.com/googleapis/python-api-core/commit/ce1adf395982ede157c0f25a920946bb52789873))
+
+
+### Bug Fixes
+
+* handle bare 'grpc.Call' in 'from_grpc_error' ([#298](https://www.github.com/googleapis/python-api-core/issues/298)) ([060b339](https://www.github.com/googleapis/python-api-core/commit/060b339e3af296dd1772bfc1b4a0d2b4264cae1f))
+
+### [2.2.2](https://www.github.com/googleapis/python-api-core/compare/v2.2.1...v2.2.2) (2021-11-02)
+
+
+### Bug Fixes
+
+* make 'gapic_v1.method.DEFAULT' a typed object ([#292](https://www.github.com/googleapis/python-api-core/issues/292)) ([ffc51f0](https://www.github.com/googleapis/python-api-core/commit/ffc51f03c7ce5d9f009ba859b8df385d52925578))
+
+### [2.2.1](https://www.github.com/googleapis/python-api-core/compare/v2.2.0...v2.2.1) (2021-10-26)
+
+
+### Bug Fixes
+
+* revert "fix: do not error on LROs with no response or error" ([#294](https://www.github.com/googleapis/python-api-core/issues/294)) ([9e6091e](https://www.github.com/googleapis/python-api-core/commit/9e6091ee59a30e72a6278b369f6a08e7aef32f22))
+
+## [2.2.0](https://www.github.com/googleapis/python-api-core/compare/v2.1.1...v2.2.0) (2021-10-25)
+
+
+### Features
+
+* add 'GoogleAPICallError.error_details' property ([#286](https://www.github.com/googleapis/python-api-core/issues/286)) ([ef6f0fc](https://www.github.com/googleapis/python-api-core/commit/ef6f0fcfdfe771172056e35e3c990998b3b00416))
+
+### [2.1.1](https://www.github.com/googleapis/python-api-core/compare/v2.1.0...v2.1.1) (2021-10-13)
+
+
+### Bug Fixes
+
+* add mypy checking + 'py.typed' file ([#290](https://www.github.com/googleapis/python-api-core/issues/290)) ([0023ee1](https://www.github.com/googleapis/python-api-core/commit/0023ee1fe0e8b80c7a9e8987e0f322a829e5d613))
+
+## [2.1.0](https://www.github.com/googleapis/python-api-core/compare/v2.0.1...v2.1.0) (2021-10-05)
+
+
+### Features
+
+* add grpc transcoding + tests ([#259](https://www.github.com/googleapis/python-api-core/issues/259)) ([afe0fa1](https://www.github.com/googleapis/python-api-core/commit/afe0fa14c21289c8244606a9f81544cff8ac5f7c))
+* Add helper function to format query_params for rest transport. ([#275](https://www.github.com/googleapis/python-api-core/issues/275)) ([1c5eb4d](https://www.github.com/googleapis/python-api-core/commit/1c5eb4df93d78e791082d9282330ebf0faacd222))
+* add support for Python 3.10 ([#284](https://www.github.com/googleapis/python-api-core/issues/284)) ([a422a5d](https://www.github.com/googleapis/python-api-core/commit/a422a5d72cb6f363d57e7a4effe421ba8e049cde))
+
+### [2.0.1](https://www.github.com/googleapis/python-api-core/compare/v2.0.0...v2.0.1) (2021-08-31)
+
+
+### Bug Fixes
+
+* do not error on LROs with no response or error ([#258](https://www.github.com/googleapis/python-api-core/issues/258)) ([618f192](https://www.github.com/googleapis/python-api-core/commit/618f19201af729205892fcecd9c8e315ba3174a3))
+
+## [2.0.0](https://www.github.com/googleapis/python-api-core/compare/v2.0.0-b1...v2.0.0) (2021-08-18)
+
+### ⚠ BREAKING CHANGES
+
+* drop support for Python 2.7 / 3.5 ([#212](https://www.github.com/googleapis/python-api-core/issues/212)) ([a30f004](https://www.github.com/googleapis/python-api-core/commit/a30f004e74f709d46e905dd819c71f43354e9ac9))
+
+### Bug Fixes
+
+* bump grpcio version to use stable aio API ([#234](https://www.github.com/googleapis/python-api-core/issues/234)) ([bdbf889](https://www.github.com/googleapis/python-api-core/commit/bdbf889210b709d7c1945f2160bcba9161b4dd2e))
+* strip trailing _ from field mask paths ([#228](https://www.github.com/googleapis/python-api-core/issues/228)) ([ff6ef1b](https://www.github.com/googleapis/python-api-core/commit/ff6ef1bd07fa68307b7c82c910416d770e7b3416))
+
+## [2.0.0b1](https://www.github.com/googleapis/python-api-core/compare/v1.31.1...v2.0.0b1) (2021-08-03)
+
+
+### ⚠ BREAKING CHANGES
+
+* drop support for Python 2.7 / 3.5 ([#212](https://www.github.com/googleapis/python-api-core/issues/212)) ([a30f004](https://www.github.com/googleapis/python-api-core/commit/a30f004e74f709d46e905dd819c71f43354e9ac9))
+
+### Bug Fixes
+
+* strip trailing _ from field mask paths ([#228](https://www.github.com/googleapis/python-api-core/issues/228)) ([ff6ef1b](https://www.github.com/googleapis/python-api-core/commit/ff6ef1bd07fa68307b7c82c910416d770e7b3416))
+
+### [1.31.1](https://www.github.com/googleapis/python-api-core/compare/v1.31.0...v1.31.1) (2021-07-26)
+
+
+### Bug Fixes
+
+* add 'requests.exceptions.ChunkedEncodingError' to retryable exceptions ([#237](https://www.github.com/googleapis/python-api-core/issues/237)) ([5e540f2](https://www.github.com/googleapis/python-api-core/commit/5e540f28493cc3e13260458a8d1c6a1abb2ed313))
+
+
+### Documentation
+
+* add Samples section to CONTRIBUTING.rst ([#229](https://www.github.com/googleapis/python-api-core/issues/229)) ([a12c051](https://www.github.com/googleapis/python-api-core/commit/a12c0516c42918b05415835029717814353b883b))
+
+## [1.31.0](https://www.github.com/googleapis/python-api-core/compare/v1.30.0...v1.31.0) (2021-07-07)
+
+
+### Features
+
+* add ServiceUnavailable exception to polling retries ([#184](https://www.github.com/googleapis/python-api-core/issues/184)) ([11032cf](https://www.github.com/googleapis/python-api-core/commit/11032cf08ecc16dd252a6cda8b33b0b28ec4f4ba))
+
+
+### Bug Fixes
+
+* undprecate entity factory helpers ([#101](https://www.github.com/googleapis/python-api-core/issues/101)) ([1fbee03](https://www.github.com/googleapis/python-api-core/commit/1fbee03495a136eef3d6aaa5ea0aadd6e4b58e8b)), closes [#100](https://www.github.com/googleapis/python-api-core/issues/100)
+
+## [1.30.0](https://www.github.com/googleapis/python-api-core/compare/v1.29.0...v1.30.0) (2021-06-08)
+
+
+### Features
+
+* add iterator capability to paged iterators ([#200](https://www.github.com/googleapis/python-api-core/issues/200)) ([3487d68](https://www.github.com/googleapis/python-api-core/commit/3487d68bdab6f20e2ab931c8283f63c94862cf31))
+
+## [1.29.0](https://www.github.com/googleapis/python-api-core/compare/v1.28.0...v1.29.0) (2021-06-02)
+
+
+### Features
+
+* HTTPIterator now accepts a page_size parameter to control page … ([#197](https://www.github.com/googleapis/python-api-core/issues/197)) ([a421913](https://www.github.com/googleapis/python-api-core/commit/a4219137a5bfcf2a6f44780ecdbf475c1129e461))
+
+
+### Documentation
+
+* fix broken links in multiprocessing.rst ([#195](https://www.github.com/googleapis/python-api-core/issues/195)) ([8d8bc51](https://www.github.com/googleapis/python-api-core/commit/8d8bc5150ee5543b4aeb2c271da034a5305d1436))
+
+## [1.28.0](https://www.github.com/googleapis/python-api-core/compare/v1.27.0...v1.28.0) (2021-05-20)
+
+
+### Bug Fixes
+
+* require google-auth>=1.25.0 ([#190](https://www.github.com/googleapis/python-api-core/issues/190)) ([155da5e](https://www.github.com/googleapis/python-api-core/commit/155da5e18cc2fdcfa57de6f956b7d078e79cd4b7))
+
+
+### Miscellaneous Chores
+
+* release 1.28.0 ([#192](https://www.github.com/googleapis/python-api-core/issues/192)) ([11b5da4](https://www.github.com/googleapis/python-api-core/commit/11b5da426a842541ca2b861d3387fc312b3f5b60))
+
+## [1.27.0](https://www.github.com/googleapis/python-api-core/compare/v1.26.3...v1.27.0) (2021-05-18)
+
+
+### Features
+
+* Add support for `rest/` token in `x-goog-api-client` header ([#189](https://www.github.com/googleapis/python-api-core/issues/189)) ([15aca6b](https://www.github.com/googleapis/python-api-core/commit/15aca6b288b2ec5ce0251e442e1dfa7f52e1b124))
+* retry google.auth TransportError and requests ConnectionError ([#178](https://www.github.com/googleapis/python-api-core/issues/178)) ([6ae04a8](https://www.github.com/googleapis/python-api-core/commit/6ae04a8d134fffe13f06081e15f9723c1b2ea334))
+
+### [1.26.3](https://www.github.com/googleapis/python-api-core/compare/v1.26.2...v1.26.3) (2021-03-25)
+
+
+### Bug Fixes
+
+* skip empty policy bindings in `len()` and `iter()` ([#159](https://www.github.com/googleapis/python-api-core/issues/159)) ([9eaa786](https://www.github.com/googleapis/python-api-core/commit/9eaa7868164a7e98792de24d2be97f79fba22322))
+
+
+### Documentation
+
+* update python contributing guide ([#147](https://www.github.com/googleapis/python-api-core/issues/147)) ([1d76b57](https://www.github.com/googleapis/python-api-core/commit/1d76b57d1f218f7885f85dc7c052bad1ad3857ac))
+
+### [1.26.2](https://www.github.com/googleapis/python-api-core/compare/v1.26.1...v1.26.2) (2021-03-23)
+
+
+### Bug Fixes
+
+* save empty IAM policy bindings ([#155](https://www.github.com/googleapis/python-api-core/issues/155)) ([536c2ca](https://www.github.com/googleapis/python-api-core/commit/536c2cad814b8fa8cd346a3d7bd5f6b9889c4a6f))
+
+### [1.26.1](https://www.github.com/googleapis/python-api-core/compare/v1.26.0...v1.26.1) (2021-02-12)
+
+
+### Bug Fixes
+
+* add operation name to x-goog-request-params in async client ([#137](https://www.github.com/googleapis/python-api-core/issues/137)) ([7271b23](https://www.github.com/googleapis/python-api-core/commit/7271b23afddb032e49e957525704d0cd5bfa4c65))
+
+## [1.26.0](https://www.github.com/googleapis/python-api-core/compare/v1.25.1...v1.26.0) (2021-02-08)
+
+
+### Features
+
+* allow default_host and default_scopes to be passed to create_channel ([#134](https://www.github.com/googleapis/python-api-core/issues/134)) ([94c76e0](https://www.github.com/googleapis/python-api-core/commit/94c76e0873e5b2f42331d5b1ad286c1e63b61395))
+
+### [1.25.1](https://www.github.com/googleapis/python-api-core/compare/v1.25.0...v1.25.1) (2021-01-25)
+
+
+### Bug Fixes
+
+* add operation name to x-goog-request-params ([#133](https://www.github.com/googleapis/python-api-core/issues/133)) ([97cef4a](https://www.github.com/googleapis/python-api-core/commit/97cef4ad1db55938715f9ac8000d1b0ad1e71873))
+
+
+### Documentation
+
+* fix spelling errors in retry ([#131](https://www.github.com/googleapis/python-api-core/issues/131)) ([232dab0](https://www.github.com/googleapis/python-api-core/commit/232dab0ad3ef2cca0edfe707d8f90ca0ea200ba2))
+
+## [1.25.0](https://www.github.com/googleapis/python-api-core/compare/v1.24.1...v1.25.0) (2021-01-14)
+
+
+### Features
+
+* allow gRPC metadata to be passed to operations client ([#127](https://www.github.com/googleapis/python-api-core/issues/127)) ([73854e8](https://www.github.com/googleapis/python-api-core/commit/73854e897b885e9be290f2676a8a1466b4f041e4))
+
+
+### Documentation
+
+* **python:** document adding Python 3.9 support, dropping 3.5 support ([#120](https://www.github.com/googleapis/python-api-core/issues/120)) ([b51b7f5](https://www.github.com/googleapis/python-api-core/commit/b51b7f587042fe9340371c1b5c8e9adf8001c43a)), closes [#787](https://www.github.com/googleapis/python-api-core/issues/787)
+
+### [1.24.1](https://www.github.com/googleapis/python-api-core/compare/v1.24.0...v1.24.1) (2020-12-16)
+
+
+### Bug Fixes
+
+* support 'retry' for ops built from HTTP/gRPC responses ([#115](https://www.github.com/googleapis/python-api-core/issues/115)) ([7a38243](https://www.github.com/googleapis/python-api-core/commit/7a38243c351b228d103eee81fc5ae521ad1c930e)), closes [#87](https://www.github.com/googleapis/python-api-core/issues/87)
+
+## [1.24.0](https://www.github.com/googleapis/python-api-core/compare/v1.23.0...v1.24.0) (2020-12-14)
+
+
+### Features
+
+* add support for Python 3.9, drop support for Python 3.5 ([#111](https://www.github.com/googleapis/python-api-core/issues/111)) ([fdbed0f](https://www.github.com/googleapis/python-api-core/commit/fdbed0f0cbae8de21c73338a6817f8aa79cef4c9)), closes [#110](https://www.github.com/googleapis/python-api-core/issues/110)
+
+
+### Documentation
+
+* explain how to create credentials from dict ([#109](https://www.github.com/googleapis/python-api-core/issues/109)) ([5dce6d6](https://www.github.com/googleapis/python-api-core/commit/5dce6d61e7324a415c1b3ceaeec1ce1b5f1ea189))
+
+## [1.23.0](https://www.github.com/googleapis/python-api-core/compare/v1.22.4...v1.23.0) (2020-10-16)
+
+
+### Features
+
+* **api-core:** pass retry from result() to done() ([#9](https://www.github.com/googleapis/python-api-core/issues/9)) ([6623b31](https://www.github.com/googleapis/python-api-core/commit/6623b31a2040b834be808d711fa397dc428f1837))
+
+
+### Bug Fixes
+
+*  map LRO errors to library exception types ([#86](https://www.github.com/googleapis/python-api-core/issues/86)) ([a855339](https://www.github.com/googleapis/python-api-core/commit/a85533903c57be4809fe76435e298409e0903931)), closes [#15](https://www.github.com/googleapis/python-api-core/issues/15)
+* harden install to use full paths, and windows separators on windows ([#88](https://www.github.com/googleapis/python-api-core/issues/88)) ([db8e636](https://www.github.com/googleapis/python-api-core/commit/db8e636f545a8872f959e3f403cfec30ffed6c34))
+* update out-of-date comment in exceptions.py ([#93](https://www.github.com/googleapis/python-api-core/issues/93)) ([70ebe42](https://www.github.com/googleapis/python-api-core/commit/70ebe42601b3d088b3421233ef7d8245229b7265))
+
+### [1.22.4](https://www.github.com/googleapis/python-api-core/compare/v1.22.3...v1.22.4) (2020-10-05)
+
+
+### Bug Fixes
+
+* use version.py instead of pkg_resources.get_distribution ([#80](https://www.github.com/googleapis/python-api-core/issues/80)) ([d480d97](https://www.github.com/googleapis/python-api-core/commit/d480d97e41cd6705325b3b649360553a83c23f47))
+
+### [1.22.3](https://www.github.com/googleapis/python-api-core/compare/v1.22.2...v1.22.3) (2020-10-02)
+
+
+### Bug Fixes
+
+* **deps:** require six >= 1.13.0 ([#78](https://www.github.com/googleapis/python-api-core/issues/78)) ([a7a8b98](https://www.github.com/googleapis/python-api-core/commit/a7a8b98602a3eb277fdc607ac69f3bcb147f3351)), closes [/github.com/benjaminp/six/blob/c0be8815d13df45b6ae471c4c436cce8c192245d/CHANGES#L30-L31](https://www.github.com/googleapis//github.com/benjaminp/six/blob/c0be8815d13df45b6ae471c4c436cce8c192245d/CHANGES/issues/L30-L31)
+
+### [1.22.2](https://www.github.com/googleapis/python-api-core/compare/v1.22.1...v1.22.2) (2020-09-03)
+
+
+### Bug Fixes
+
+* only add quota project id if supported ([#75](https://www.github.com/googleapis/python-api-core/issues/75)) ([8f8ee78](https://www.github.com/googleapis/python-api-core/commit/8f8ee7879e4f834f3c676e535ffc41b5b9b2de62))
+
+### [1.22.1](https://www.github.com/googleapis/python-api-core/compare/v1.22.0...v1.22.1) (2020-08-12)
+
+
+### Documentation
+
+* fix spelling errors for amount in retry ([#69](https://www.github.com/googleapis/python-api-core/issues/69)) ([7bb713d](https://www.github.com/googleapis/python-api-core/commit/7bb713d13b1fe3cca58263f5e499136a84abc456))
+
+## [1.22.0](https://www.github.com/googleapis/python-api-core/compare/v1.21.0...v1.22.0) (2020-07-21)
+
+
+### Features
+
+* allow quota project to be passed to create_channel ([#58](https://www.github.com/googleapis/python-api-core/issues/58)) ([e2d9a7b](https://www.github.com/googleapis/python-api-core/commit/e2d9a7b209b7dfab300dc848fabbae8f42a2ab19))
+
+
+### Bug Fixes
+
+* _determine_timeout problem handling float type timeout ([#64](https://www.github.com/googleapis/python-api-core/issues/64)) ([2010373](https://www.github.com/googleapis/python-api-core/commit/2010373b27536d1191175624b297a709d70153fa))
+
+
+### Documentation
+
+* change the documentation for using 'six.moves.collections_abc.Mapping' instead of 'dict' in 'client_options.from_dict()' ([#53](https://www.github.com/googleapis/python-api-core/issues/53)) ([c890675](https://www.github.com/googleapis/python-api-core/commit/c890675dc9ebc084f105be81dc81c048f4f599ea))
+
+## [1.21.0](https://www.github.com/googleapis/python-api-core/compare/v1.20.1...v1.21.0) (2020-06-18)
+
+
+### Features
+
+* allow credentials files to be passed for channel creation ([#50](https://www.github.com/googleapis/python-api-core/issues/50)) ([ded92d0](https://www.github.com/googleapis/python-api-core/commit/ded92d0acdcde4295d0e5df05fda0d83783a3991))
+
+### [1.20.1](https://www.github.com/googleapis/python-api-core/compare/v1.20.0...v1.20.1) (2020-06-16)
+
+
+### Bug Fixes
+
+* **dependencies:** increase protobuf version ([#49](https://www.github.com/googleapis/python-api-core/issues/49)) ([1ba6095](https://www.github.com/googleapis/python-api-core/commit/1ba609592968c9d828449b89a3ade3bcaf5edd7f)), closes [#48](https://www.github.com/googleapis/python-api-core/issues/48)
+
+## [1.20.0](https://www.github.com/googleapis/python-api-core/compare/v1.19.1...v1.20.0) (2020-06-09)
+
+
+### Features
+
+* allow disabling response stream pre-fetch ([#30](https://www.github.com/googleapis/python-api-core/issues/30)) ([74e0b0f](https://www.github.com/googleapis/python-api-core/commit/74e0b0f8387207933c120af15b2bb5d175dd8f84)), closes [#25](https://www.github.com/googleapis/python-api-core/issues/25)
+
+### [1.19.1](https://www.github.com/googleapis/python-api-core/compare/v1.19.0...v1.19.1) (2020-06-06)
+
+
+### Bug Fixes
+
+* bump up grpcio minimum version to 1.29.0 ([#41](https://www.github.com/googleapis/python-api-core/issues/41)) ([4b11422](https://www.github.com/googleapis/python-api-core/commit/4b114221b3ae01eee540bedf47381c3b7c214b0c))
+
+## [1.19.0](https://www.github.com/googleapis/python-api-core/compare/v1.18.0...v1.19.0) (2020-06-05)
+
+
+### Features
+
+* **client_options:** add new client options 'quota_project_id', 'scopes', and 'credentials_file' ([a582936](https://www.github.com/googleapis/python-api-core/commit/a58293601d6da90c499d404e634a979a6cae9708))
+
+## [1.18.0](https://www.github.com/googleapis/python-api-core/compare/v1.17.0...v1.18.0) (2020-06-04)
+
+
+### Features
+
+* [CBT-6 helper] Exposing Retry._deadline as a property ([#20](https://www.github.com/googleapis/python-api-core/issues/20)) ([7be1e59](https://www.github.com/googleapis/python-api-core/commit/7be1e59e9d75c112f346d2b76dce3dd60e3584a1))
+* add client_encryped_cert_source to ClientOptions ([#31](https://www.github.com/googleapis/python-api-core/issues/31)) ([e4eaec0](https://www.github.com/googleapis/python-api-core/commit/e4eaec0ff255114138d3715280f86d34d861a6fa))
+* AsyncIO Integration [Part 2] ([#28](https://www.github.com/googleapis/python-api-core/issues/28)) ([dd9b2f3](https://www.github.com/googleapis/python-api-core/commit/dd9b2f38a70e85952cc05552ec8070cdf29ddbb4)), closes [#23](https://www.github.com/googleapis/python-api-core/issues/23)
+* First batch of AIO integration ([#26](https://www.github.com/googleapis/python-api-core/issues/26)) ([a82f289](https://www.github.com/googleapis/python-api-core/commit/a82f2892b8f219b82e120e6ed9f4070869c28be7))
+* third batch of AsyncIO integration ([#29](https://www.github.com/googleapis/python-api-core/issues/29)) ([7d8d580](https://www.github.com/googleapis/python-api-core/commit/7d8d58075a92e93662747d36a2d55b5e9f0943e1))
+
+## [1.17.0](https://www.github.com/googleapis/python-api-core/compare/v1.16.0...v1.17.0) (2020-04-14)
+
+
+### Features
+
+* **api_core:** add retry param into PollingFuture() and it's inheritors ([#9923](https://www.github.com/googleapis/python-api-core/issues/9923)) ([14f1f34](https://www.github.com/googleapis/python-api-core/commit/14f1f34e013c90fed2da2918625083d299fda557)), closes [#6197](https://www.github.com/googleapis/python-api-core/issues/6197)
+* **api-core:** add client_cert_source to ClientOptions ([#17](https://www.github.com/googleapis/python-api-core/issues/17)) ([748c935](https://www.github.com/googleapis/python-api-core/commit/748c935d4cf03a1f04fba9139c3c3150fd694d88))
+
+
+### Bug Fixes
+
+* consume part of StreamingResponseIterator to support failure while under a retry context ([#10206](https://www.github.com/googleapis/python-api-core/issues/10206)) ([2b103b6](https://www.github.com/googleapis/python-api-core/commit/2b103b60ece16a1e1bc98cfda7ec375191a90f75))
+
+## 1.16.0
+
+01-13-2020 14:19 PST
+
+### New Features
+
+- feat(storage): support optionsRequestedPolicyVersion ([#9989](https://github.com/GoogleCloudPlatform/google-cloud-python/pull/9989))
+- feat(api_core): support version 3 policy bindings ([#9869](https://github.com/GoogleCloudPlatform/google-cloud-python/pull/9869))
+
+## 1.15.0
+
+12-16-2019 15:27 PST
+
+### New Features
+- Make the last retry happen at deadline. ([#9873](https://github.com/googleapis/google-cloud-python/pull/9873))
+- Add a repr method for ClientOptions. ([#9849](https://github.com/googleapis/google-cloud-python/pull/9849))
+- Simplify `from_rfc3339` methods. ([#9641](https://github.com/googleapis/google-cloud-python/pull/9641))
+- Provide a `raw_page` field for `page_iterator.Page`. ([#9486](https://github.com/googleapis/google-cloud-python/pull/9486))
+
+### Documentation
+- Add Python 2 sunset banner to documentation. ([#9036](https://github.com/googleapis/google-cloud-python/pull/9036))
+- Remove references to the old authentication credentials. ([#9456](https://github.com/googleapis/google-cloud-python/pull/9456))
+
+## 1.14.3
+
+10-07-2019 10:35 PDT
+
+
+### Implementation Changes
+- Finalize during close of 'ResumableBidiRpc' ([#9337](https://github.com/googleapis/google-cloud-python/pull/9337))
+- add on_error to Retry.__init__ ([#8892](https://github.com/googleapis/google-cloud-python/pull/8892))
+- Fix race in 'BackgroundConsumer._thread_main'. ([#8883](https://github.com/googleapis/google-cloud-python/pull/8883))
+
+### Documentation
+- Fix intersphinx reference to requests ([#9294](https://github.com/googleapis/google-cloud-python/pull/9294))
+- Fix broken links in docs. ([#9148](https://github.com/googleapis/google-cloud-python/pull/9148))
+- About of time -> amount of time ([#9052](https://github.com/googleapis/google-cloud-python/pull/9052))
+- Remove compatability badges from READMEs. ([#9035](https://github.com/googleapis/google-cloud-python/pull/9035))
+
+### Internal / Testing Changes
+- Remove CI for gh-pages, use googleapis.dev for api_core refs. ([#9085](https://github.com/googleapis/google-cloud-python/pull/9085))
+
+## 1.14.2
+
+07-30-2019 14:08 PDT
+
+
+### Documentation
+- Add client_options documentation. ([#8834](https://github.com/googleapis/google-cloud-python/pull/8834))
+
+## 1.14.1
+
+07-30-2019 12:24 PDT
+
+
+### Implementation Changes
+- Remove error log entry on clean BiDi shutdown. ([#8806](https://github.com/googleapis/google-cloud-python/pull/8806))
+- Forward 'timeout' arg from 'exception' to `_blocking_poll`. ([#8735](https://github.com/googleapis/google-cloud-python/pull/8735))
+
+### Documentation
+- Update intersphinx mapping for requests. ([#8805](https://github.com/googleapis/google-cloud-python/pull/8805))
+- Link to googleapis.dev documentation in READMEs. ([#8705](https://github.com/googleapis/google-cloud-python/pull/8705))
+
+## 1.14.0
+
+07-17-2019 13:16 PDT
+
+
+### New Features
+- Firestore: Add `should_terminate` predicate for clean BiDi shutdown. ([#8650](https://github.com/googleapis/google-cloud-python/pull/8650))
+
+### Dependencies
+- Update pins of 'googleapis-common-protos. ([#8688](https://github.com/googleapis/google-cloud-python/pull/8688))
+
+### Documentation
+- Add compatibility check badges to READMEs. ([#8288](https://github.com/googleapis/google-cloud-python/pull/8288))
+
+### Internal / Testing Changes
+- All: Add docs job to publish to googleapis.dev. ([#8464](https://github.com/googleapis/google-cloud-python/pull/8464))
+
+## 1.13.0
+
+06-24-2019 10:34 PDT
+
+### New Features
+- Add `client_options.ClientOptions` object. ([#8265](https://github.com/googleapis/google-cloud-python/pull/8265))
+
+## 1.12.0
+
+06-18-2019 12:37 PDT
+
+
+### New Features
+- Add Throttling to Bidi Reopening. Mitigates ResumableBidiRpc consuming 100% CPU ([#8193](https://github.com/googleapis/google-cloud-python/pull/8193))
+
+## 1.11.1
+
+05-28-2019 11:19 PDT
+
+
+### Implementation Changes
+- Classify 503 Service Unavailable errors as transient. ([#8182](https://github.com/googleapis/google-cloud-python/pull/8182))
+
+### Dependencies
+- Pin `grpcio < 2.0dev`. ([#8182](https://github.com/googleapis/google-cloud-python/pull/8182))
+
+### Internal / Testing Changes
+- Add parameterized test for `from_rfc3339` with nanos ([#7675](https://github.com/googleapis/google-cloud-python/pull/7675))
+- Unbreak pytype by silencing a false positive. ([#8106](https://github.com/googleapis/google-cloud-python/pull/8106))
+
+## 1.11.0
+
+05-15-2019 10:29 PDT
+
+### New Features
+
+- Refactor 'client_info' support. ([#7849](https://github.com/googleapis/google-cloud-python/pull/7849))
+
+## 1.10.0
+
+04-29-2019 10:12 PDT
+
+### Implementation Changes
+
+- Append leading zeros for nanosecond precision DateTimes
+  ([#7663](https://github.com/googleapis/google-cloud-python/pull/7663))
+
+### New Features
+
+- Add `user_agent` property to `ClientInfo`
+  ([#7799](https://github.com/googleapis/google-cloud-python/pull/7799))
+
+## 1.9.0
+
+04-05-2019 10:38 PDT
+
+
+### Implementation Changes
+- Allow passing metadata as part of creating a bidi ([#7514](https://github.com/googleapis/google-cloud-python/pull/7514))
+
+### Internal / Testing Changes
+- Update setup.py
+- API Core: specify a pytype output directory in setup.cfg. ([#7639](https://github.com/googleapis/google-cloud-python/pull/7639))
+
+## 1.8.2
+
+03-22-2019 16:27 PDT
+
+
+### Implementation Changes
+- Remove classifier for Python 3.4 for end-of-life. ([#7535](https://github.com/googleapis/google-cloud-python/pull/7535))
+
+### Internal / Testing Changes
+- When re-opening a `ResumableBidiRPC` set `_request_queue_generator` to `None`. ([#7548](https://github.com/googleapis/google-cloud-python/pull/7548))
+
+## 1.8.1
+
+03-12-2019 12:45 PDT
+
+### Implementation Changes
+- Protect the creation of a background thread in BackgroundConsumer and wait on it starting. ([#7499](https://github.com/googleapis/google-cloud-python/pull/7499))
+
+## 1.8.0
+
+02-23-2019 15:46 PST
+
+
+### New Features
+- Add support to unwrap Anys into wrapped pb2 objects. ([#7430](https://github.com/googleapis/google-cloud-python/pull/7430))
+- Add `Operation.deserialize`. ([#7427](https://github.com/googleapis/google-cloud-python/pull/7427))
+
+### Documentation
+- Updated client library documentation URLs. ([#7307](https://github.com/googleapis/google-cloud-python/pull/7307))
+
+### Internal / Testing Changes
+- Fix new lint failure. ([#7382](https://github.com/googleapis/google-cloud-python/pull/7382))
+
+## 1.7.0
+
+12-17-2018 13:56 PST
+
+### New Features
+- Support converting `DatetimeWithNanos` to / from `google.protobuf.timestamp_pb2.Timestamp`. ([#6919](https://github.com/googleapis/google-cloud-python/pull/6919))
+
+### Documentation
+- Document Python 2 deprecation. ([#6910](https://github.com/googleapis/google-cloud-python/pull/6910))
+- Add usage example for `google.api_core.iam.Polcy`. ([#6855](https://github.com/googleapis/google-cloud-python/pull/6855))
+
+### Internal / Testing Changes
+- Work around pytype big for `ABCMeta.register`. ([#6873](https://github.com/googleapis/google-cloud-python/pull/6873))
+
+## 1.6.0
+
+11-30-2018 12:45 PST
+
+
+### Implementation Changes
+- Import stdlib ABCs from 'collections.abc' rather than 'collections'. ([#6451](https://github.com/googleapis/google-cloud-python/pull/6451))
+
+### New Features
+- Move google.cloud.iam (core) to google.api_core.iam ([#6740](https://github.com/googleapis/google-cloud-python/pull/6740))
+- Add bidi support to api_core. ([#6191](https://github.com/googleapis/google-cloud-python/pull/6191))
+
+### Documentation
+- Fix typo ([#6532](https://github.com/googleapis/google-cloud-python/pull/6532))
+
+### Internal / Testing Changes
+- blacken api_core and core ([#6668](https://github.com/googleapis/google-cloud-python/pull/6668))
+
+## 1.5.2
+
+11-09-2018 14:22 PST
+
+
+### Implementation Changes
+- Retry transient errors in 'PollingFuture.result'. ([#6305](https://github.com/googleapis/google-cloud-python/pull/6305))
+
+### Dependencies
+- Remove hyphen from named extra in api_core. ([#6468](https://github.com/googleapis/google-cloud-python/pull/6468))
+- Bump minimum 'api_core' version for all GAPIC libs to 1.4.1. ([#6391](https://github.com/googleapis/google-cloud-python/pull/6391))
+- Avoid broken 'google-common-apis 1.5.4' release. ([#6355](https://github.com/googleapis/google-cloud-python/pull/6355))
+
+## 1.5.1
+
+10-29-2018 13:29 PDT
+
+### Implementation Changes
+- Don't URL-encode slashes in gRPC request headers. ([#6310](https://github.com/googleapis/google-cloud-python/pull/6310))
+
+### Internal / Testing Changes
+- Back out changes from [#6267](https://github.com/googleapis/google-cloud-python/pull/6267) / `api_core-1.6.0a1` release. ([#6328](https://github.com/googleapis/google-cloud-python/pull/6328))
+
+## 1.5.0
+
+### New Features
+- Add bidi, Bidirection Streaming, to api-core ([#6211](https://github.com/GoogleCloudPlatform/google-cloud-python/pull/6211))
+
+### Internal / Testing Changes
+- Use new Nox ([#6175](https://github.com/GoogleCloudPlatform/google-cloud-python/pull/6175))
+
+## 1.4.1
+
+### Dependencies
+- Pin minimum protobuf dependency to 3.4.0. ([#6132](https://github.com/GoogleCloudPlatform/google-cloud-python/pull/6132))
+
+### Internal / Testing Changes
+- Add type-checking via pytype to api_core. ([#6116](https://github.com/GoogleCloudPlatform/google-cloud-python/pull/6116))
+
+## 1.4.0
+
+### Dependencies
+
+- Add support for gRPC connection management (available when using optional grpc_gcp dependency) ([#5553](https://github.com/GoogleCloudPlatform/google-cloud-python/pull/5553)) ([#5904](https://github.com/GoogleCloudPlatform/google-cloud-python/pull/5904))
+- Update classifiers to drop Python 3.4 and add Python 3.7 ([#5702](https://github.com/GoogleCloudPlatform/google-cloud-python/pull/5702))
+
+## 1.3.0
+
+### New Features
+
+- Add protobuf_helpers.field_mask to calculate a field mask from two messages (#5320)
+
+## 1.2.1
+
+### Implementation Changes
+- Make client_info work without gRPC installed. (#5075)
+- Rename `x-goog-header-params` to `x-goog-request-params` (#5495)
+
+## 1.2.0
+
+### Implementation Changes
+- Add close method to grpc Channel (#5333)
+
+### Internal / Testing Changes
+- Fix tests after grpcio update (#5333)
+- Add Test runs for Python 3.7 and remove 3.4 (#5295)
+
+## 1.1.2
+
+### Packaging
+- Update setuptools before packaging (#5265)
+
+## 1.1.1
+
+### Internal / Testing Changes
+- Use `install_requires` for platform dependencies instead of `extras_require` (#4991)
+- Update trove classifer to '5 - Production/Stable'
+
+## 1.1.0
+
+### Interface additions
+
+- Add `datetime_helpers.DatetimeWithNanoSeconds` (#4979)
+
+### Implementation changes
+
+- Use a class to wrap grpc streaming errors instead of monkey-patching (#4995)
+
+## 1.0.0
+
+This is the stable v1.0.0 release of google-api-core for Python. Releases after
+this will not contain breaking changes.
+
+### Interface changes and additions
+
+- Made `api_core.page_iterator.PageIterator.item_to_value` public
+- Added ability to specify retry for `Operation` and `polling.Future`. (#4922)
+
+## 0.1.4
+
+### New Features
+
+- Add `ChannelStub` to `grpc_helpers` for testing gRPC-based clients. (#4705)
+
+### Notable Implementation Changes
+
+- Fix handling of gapic metadata when specified as `None`. (#4701)
+
+## 0.1.3
+
+### Notable Implementation Changes
+
+- Apply scopes to explicitly provided credentials if needed (#4594).
+- Removing `google.api_core.gapic_v1.method.METRICS_METADATA_KEY`. It
+  can be accessed via
+  `google.api_core.gapic_v1.client_info.METRICS_METADATA_KEY` (#4588).
+
+### Dependencies
+
+- Upgrading to latest `grpcio==1.8.2` (#4642). For details, see
+  related gRPC [bug](https://github.com/grpc/grpc/issues/9688)
+  and [fix](https://github.com/grpc/grpc/pull/13665).
+
+PyPI: https://pypi.org/project/google-api-core/0.1.3/
+
+## 0.1.2
+
+- Upgrading `concurrent.futures` backport from `>= 3.0.0`
+  to `>= 3.2.0` (#4521).
+- Moved `datetime`-related helpers from `google.cloud.core` to
+  `google.api_core.datetime_helpers` (#4399).
+- Added missing `client_info` to `gapic_v1/__init__.py`'s
+  `__all__` (#4567).
+- Added helpers for routing headers to `gapic_v1` (#4336).
+
+PyPI: https://pypi.org/project/google-api-core/0.1.2/
+
+## 0.1.1
+
+### Dependencies
+
+- Upgrading `grpcio` dependency from `1.2.0, < 1.6dev` to `>= 1.7.0` (#4280)
+
+PyPI: https://pypi.org/project/google-api-core/0.1.1/
+
+## 0.1.0
+
+Initial release
+
+Prior to being separated, this package was developed in `google-cloud-core`, so
+relevant changes from that package are included here.
+
+- Add google.api.core.gapic_v1.config (#4022)
+- Add google.api.core.helpers.grpc_helpers (#4041)
+- Add google.api.core.gapic_v1.method (#4057)
+- Add wrap_with_paging (#4067)
+- Add grpc_helpers.create_channel (#4069)
+- Add DEFAULT sentinel for gapic_v1.method (#4079)
+- Remove `googleapis-common-protos` from deps in non-`core` packages. (#4098)
+- Add google.api.core.operations_v1 (#4081)
+- Fix test assertion in test_wrap_method_with_overriding_retry_deadline (#4131)
+- Add google.api.core.helpers.general_helpers.wraps (#4166)
+- Update Docs with Python Setup Guide (#4187)
+- Move modules in google.api.core.helpers up one level, delete google.api.core.helpers. (#4196)
+- Clarify that PollingFuture timeout is in seconds. (#4201)
+- Add api_core package (#4210)
+- Replace usage of google.api.core with google.api_core (#4221)
+- Add google.api_core.gapic_v2.client_info (#4225)
+- Fix how api_core.operation populates exception errors (#4231)
+- Fix bare except (#4250)
+- Fix parsing of API errors with Unicode err message (#4251)
+- Port gax proto helper methods (#4249)
+- Remove gapic_v1.method.wrap_with_paging (#4257)
+- Add final set of protobuf helpers to api_core (#4259)
+
+PyPI: https://pypi.org/project/google-api-core/0.1.0/
diff --git a/CODE_OF_CONDUCT.md b/CODE_OF_CONDUCT.md
new file mode 100644
index 0000000..039f436
--- /dev/null
+++ b/CODE_OF_CONDUCT.md
@@ -0,0 +1,95 @@
+<!-- # Generated by synthtool. DO NOT EDIT! !-->
+# Code of Conduct
+
+## Our Pledge
+
+In the interest of fostering an open and welcoming environment, we as
+contributors and maintainers pledge to making participation in our project and
+our community a harassment-free experience for everyone, regardless of age, body
+size, disability, ethnicity, gender identity and expression, level of
+experience, education, socio-economic status, nationality, personal appearance,
+race, religion, or sexual identity and orientation.
+
+## Our Standards
+
+Examples of behavior that contributes to creating a positive environment
+include:
+
+*   Using welcoming and inclusive language
+*   Being respectful of differing viewpoints and experiences
+*   Gracefully accepting constructive criticism
+*   Focusing on what is best for the community
+*   Showing empathy towards other community members
+
+Examples of unacceptable behavior by participants include:
+
+*   The use of sexualized language or imagery and unwelcome sexual attention or
+    advances
+*   Trolling, insulting/derogatory comments, and personal or political attacks
+*   Public or private harassment
+*   Publishing others' private information, such as a physical or electronic
+    address, without explicit permission
+*   Other conduct which could reasonably be considered inappropriate in a
+    professional setting
+
+## Our Responsibilities
+
+Project maintainers are responsible for clarifying the standards of acceptable
+behavior and are expected to take appropriate and fair corrective action in
+response to any instances of unacceptable behavior.
+
+Project maintainers have the right and responsibility to remove, edit, or reject
+comments, commits, code, wiki edits, issues, and other contributions that are
+not aligned to this Code of Conduct, or to ban temporarily or permanently any
+contributor for other behaviors that they deem inappropriate, threatening,
+offensive, or harmful.
+
+## Scope
+
+This Code of Conduct applies both within project spaces and in public spaces
+when an individual is representing the project or its community. Examples of
+representing a project or community include using an official project e-mail
+address, posting via an official social media account, or acting as an appointed
+representative at an online or offline event. Representation of a project may be
+further defined and clarified by project maintainers.
+
+This Code of Conduct also applies outside the project spaces when the Project
+Steward has a reasonable belief that an individual's behavior may have a
+negative impact on the project or its community.
+
+## Conflict Resolution
+
+We do not believe that all conflict is bad; healthy debate and disagreement
+often yield positive results. However, it is never okay to be disrespectful or
+to engage in behavior that violates the project’s code of conduct.
+
+If you see someone violating the code of conduct, you are encouraged to address
+the behavior directly with those involved. Many issues can be resolved quickly
+and easily, and this gives people more control over the outcome of their
+dispute. If you are unable to resolve the matter for any reason, or if the
+behavior is threatening or harassing, report it. We are dedicated to providing
+an environment where participants feel welcome and safe.
+
+
+Reports should be directed to *googleapis-stewards@google.com*, the
+Project Steward(s) for *Google Cloud Client Libraries*. It is the Project Steward’s duty to
+receive and address reported violations of the code of conduct. They will then
+work with a committee consisting of representatives from the Open Source
+Programs Office and the Google Open Source Strategy team. If for any reason you
+are uncomfortable reaching out to the Project Steward, please email
+opensource@google.com.
+
+We will investigate every complaint, but you may not receive a direct response.
+We will use our discretion in determining when and how to follow up on reported
+incidents, which may range from not taking action to permanent expulsion from
+the project and project-sponsored spaces. We will notify the accused of the
+report and provide them an opportunity to discuss it before any action is taken.
+The identity of the reporter will be omitted from the details of the report
+supplied to the accused. In potentially harmful situations, such as ongoing
+harassment or threats to anyone's safety, we may take action without notice.
+
+## Attribution
+
+This Code of Conduct is adapted from the Contributor Covenant, version 1.4,
+available at
+https://www.contributor-covenant.org/version/1/4/code-of-conduct.html
\ No newline at end of file
diff --git a/CONTRIBUTING.rst b/CONTRIBUTING.rst
new file mode 100644
index 0000000..6b375f0
--- /dev/null
+++ b/CONTRIBUTING.rst
@@ -0,0 +1,257 @@
+############
+Contributing
+############
+
+#. **Please sign one of the contributor license agreements below.**
+#. Fork the repo, develop and test your code changes, add docs.
+#. Make sure that your commit messages clearly describe the changes.
+#. Send a pull request. (Please Read: `Faster Pull Request Reviews`_)
+
+.. _Faster Pull Request Reviews: https://github.com/kubernetes/community/blob/master/contributors/guide/pull-requests.md#best-practices-for-faster-reviews
+
+.. contents:: Here are some guidelines for hacking on the Google Cloud Client libraries.
+
+***************
+Adding Features
+***************
+
+In order to add a feature:
+
+- The feature must be documented in both the API and narrative
+  documentation.
+
+- The feature must work fully on the following CPython versions:
+  3.6, 3.7, 3.8, 3.9, and 3.10 on both UNIX and Windows.
+
+- The feature must not add unnecessary dependencies (where
+  "unnecessary" is of course subjective, but new dependencies should
+  be discussed).
+
+****************************
+Using a Development Checkout
+****************************
+
+You'll have to create a development environment using a Git checkout:
+
+- While logged into your GitHub account, navigate to the
+  ``python-api-core`` `repo`_ on GitHub.
+
+- Fork and clone the ``python-api-core`` repository to your GitHub account by
+  clicking the "Fork" button.
+
+- Clone your fork of ``python-api-core`` from your GitHub account to your local
+  computer, substituting your account username and specifying the destination
+  as ``hack-on-python-api-core``.  E.g.::
+
+   $ cd ${HOME}
+   $ git clone git@github.com:USERNAME/python-api-core.git hack-on-python-api-core
+   $ cd hack-on-python-api-core
+   # Configure remotes such that you can pull changes from the googleapis/python-api-core
+   # repository into your local repository.
+   $ git remote add upstream git@github.com:googleapis/python-api-core.git
+   # fetch and merge changes from upstream into main
+   $ git fetch upstream
+   $ git merge upstream/main
+
+Now your local repo is set up such that you will push changes to your GitHub
+repo, from which you can submit a pull request.
+
+To work on the codebase and run the tests, we recommend using ``nox``,
+but you can also use a ``virtualenv`` of your own creation.
+
+.. _repo: https://github.com/googleapis/python-api-core
+
+Using ``nox``
+=============
+
+We use `nox <https://nox.readthedocs.io/en/latest/>`__ to instrument our tests.
+
+- To test your changes, run unit tests with ``nox``::
+    $ nox -s unit
+
+- To run a single unit test::
+
+    $ nox -s unit-3.10 -- -k <name of test>
+
+
+  .. note::
+
+    The unit tests tests are described in the ``noxfile.py`` files
+    in each directory.
+
+.. nox: https://pypi.org/project/nox/
+
+*****************************************
+I'm getting weird errors... Can you help?
+*****************************************
+
+If the error mentions ``Python.h`` not being found,
+install ``python-dev`` and try again.
+On Debian/Ubuntu::
+
+  $ sudo apt-get install python-dev
+
+************
+Coding Style
+************
+- We use the automatic code formatter ``black``. You can run it using
+  the nox session ``blacken``. This will eliminate many lint errors. Run via::
+
+   $ nox -s blacken
+
+- PEP8 compliance is required, with exceptions defined in the linter configuration.
+  If you have ``nox`` installed, you can test that you have not introduced
+  any non-compliant code via::
+
+   $ nox -s lint
+
+- In order to make ``nox -s lint`` run faster, you can set some environment
+  variables::
+
+   export GOOGLE_CLOUD_TESTING_REMOTE="upstream"
+   export GOOGLE_CLOUD_TESTING_BRANCH="main"
+
+  By doing this, you are specifying the location of the most up-to-date
+  version of ``python-api-core``. The the suggested remote name ``upstream``
+  should point to the official ``googleapis`` checkout and the
+  the branch should be the main branch on that remote (``main``).
+
+- This repository contains configuration for the
+  `pre-commit <https://pre-commit.com/>`__ tool, which automates checking
+  our linters during a commit.  If you have it installed on your ``$PATH``,
+  you can enable enforcing those checks via:
+
+.. code-block:: bash
+
+   $ pre-commit install
+   pre-commit installed at .git/hooks/pre-commit
+
+Exceptions to PEP8:
+
+- Many unit tests use a helper method, ``_call_fut`` ("FUT" is short for
+  "Function-Under-Test"), which is PEP8-incompliant, but more readable.
+  Some also use a local variable, ``MUT`` (short for "Module-Under-Test").
+
+
+*************
+Test Coverage
+*************
+
+- The codebase *must* have 100% test statement coverage after each commit.
+  You can test coverage via ``nox -s cover``.
+
+******************************************************
+Documentation Coverage and Building HTML Documentation
+******************************************************
+
+If you fix a bug, and the bug requires an API or behavior modification, all
+documentation in this package which references that API or behavior must be
+changed to reflect the bug fix, ideally in the same commit that fixes the bug
+or adds the feature.
+
+Build the docs via:
+
+   $ nox -s docs
+
+*************************
+Samples and code snippets
+*************************
+
+Code samples and snippets live in the `samples/` catalogue. Feel free to
+provide more examples, but make sure to write tests for those examples.
+Each folder containing example code requires its own `noxfile.py` script
+which automates testing. If you decide to create a new folder, you can
+base it on the `samples/snippets` folder (providing `noxfile.py` and
+the requirements files).
+
+The tests will run against a real Google Cloud Project, so you should
+configure them just like the System Tests.
+
+- To run sample tests, you can execute::
+
+   # Run all tests in a folder
+   $ cd samples/snippets
+   $ nox -s py-3.8
+
+   # Run a single sample test
+   $ cd samples/snippets
+   $ nox -s py-3.8 -- -k <name of test>
+
+********************************************
+Note About ``README`` as it pertains to PyPI
+********************************************
+
+The `description on PyPI`_ for the project comes directly from the
+``README``. Due to the reStructuredText (``rst``) parser used by
+PyPI, relative links which will work on GitHub (e.g. ``CONTRIBUTING.rst``
+instead of
+``https://github.com/googleapis/python-api-core/blob/main/CONTRIBUTING.rst``)
+may cause problems creating links or rendering the description.
+
+.. _description on PyPI: https://pypi.org/project/google-api-core
+
+
+*************************
+Supported Python Versions
+*************************
+
+We support:
+
+-  `Python 3.6`_
+-  `Python 3.7`_
+-  `Python 3.8`_
+-  `Python 3.9`_
+-  `Python 3.10`_
+
+.. _Python 3.6: https://docs.python.org/3.6/
+.. _Python 3.7: https://docs.python.org/3.7/
+.. _Python 3.8: https://docs.python.org/3.8/
+.. _Python 3.9: https://docs.python.org/3.9/
+.. _Python 3.10: https://docs.python.org/3.10/
+
+
+Supported versions can be found in our ``noxfile.py`` `config`_.
+
+.. _config: https://github.com/googleapis/python-api-core/blob/main/noxfile.py
+
+
+We also explicitly decided to support Python 3 beginning with version 3.6.
+Reasons for this include:
+
+-  Encouraging use of newest versions of Python 3
+-  Taking the lead of `prominent`_ open-source `projects`_
+-  `Unicode literal support`_ which allows for a cleaner codebase that
+   works in both Python 2 and Python 3
+
+.. _prominent: https://docs.djangoproject.com/en/1.9/faq/install/#what-python-version-can-i-use-with-django
+.. _projects: http://flask.pocoo.org/docs/0.10/python3/
+.. _Unicode literal support: https://www.python.org/dev/peps/pep-0414/
+
+**********
+Versioning
+**********
+
+This library follows `Semantic Versioning`_.
+
+.. _Semantic Versioning: http://semver.org/
+
+Some packages are currently in major version zero (``0.y.z``), which means that
+anything may change at any time and the public API should not be considered
+stable.
+
+******************************
+Contributor License Agreements
+******************************
+
+Before we can accept your pull requests you'll need to sign a Contributor
+License Agreement (CLA):
+
+- **If you are an individual writing original source code** and **you own the
+  intellectual property**, then you'll need to sign an
+  `individual CLA <https://developers.google.com/open-source/cla/individual>`__.
+- **If you work for a company that wants to allow you to contribute your work**,
+  then you'll need to sign a
+  `corporate CLA <https://developers.google.com/open-source/cla/corporate>`__.
+
+You can sign these electronically (just scroll to the bottom). After that,
+we'll be able to accept your pull requests.
diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..d645695
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,202 @@
+
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+
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+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
diff --git a/MANIFEST.in b/MANIFEST.in
new file mode 100644
index 0000000..e783f4c
--- /dev/null
+++ b/MANIFEST.in
@@ -0,0 +1,25 @@
+# -*- coding: utf-8 -*-
+#
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Generated by synthtool. DO NOT EDIT!
+include README.rst LICENSE
+recursive-include google *.json *.proto py.typed
+recursive-include tests *
+global-exclude *.py[co]
+global-exclude __pycache__
+
+# Exclude scripts for samples readmegen
+prune scripts/readme-gen
diff --git a/METADATA b/METADATA
new file mode 100644
index 0000000..cfe802c
--- /dev/null
+++ b/METADATA
@@ -0,0 +1,18 @@
+name: "python-api-core"
+description:
+    "This library is not meant to stand-alone. Instead it defines common "
+    "helpers used by all Google API clients."
+
+third_party {
+  url {
+    type: HOMEPAGE
+    value: "https://pypi.org/project/google-api-core/"
+  }
+  url {
+    type: GIT
+    value: "https://github.com/googleapis/python-api-core"
+  }
+  version: "v2.3.0"
+  last_upgrade_date { year: 2022 month: 1 day: 4 }
+  license_type: NOTICE
+}
diff --git a/MODULE_LICENSE_APACHE2 b/MODULE_LICENSE_APACHE2
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/MODULE_LICENSE_APACHE2
diff --git a/NOTICE b/NOTICE
new file mode 120000
index 0000000..7a694c9
--- /dev/null
+++ b/NOTICE
@@ -0,0 +1 @@
+LICENSE
\ No newline at end of file
diff --git a/README.rst b/README.rst
new file mode 100644
index 0000000..d94f3e8
--- /dev/null
+++ b/README.rst
@@ -0,0 +1,28 @@
+Core Library for Google Client Libraries
+========================================
+
+|pypi| |versions|
+
+This library is not meant to stand-alone. Instead it defines
+common helpers used by all Google API clients. For more information, see the
+`documentation`_.
+
+.. |pypi| image:: https://img.shields.io/pypi/v/google-api_core.svg
+   :target: https://pypi.org/project/google-api_core/
+.. |versions| image:: https://img.shields.io/pypi/pyversions/google-api_core.svg
+   :target: https://pypi.org/project/google-api_core/
+.. _documentation: https://googleapis.dev/python/google-api-core/latest
+
+
+Supported Python Versions
+-------------------------
+Python >= 3.6
+
+
+Unsupported Python Versions
+---------------------------
+
+Python == 2.7, Python == 3.5.
+
+The last version of this library compatible with Python 2.7 and 3.5 is
+`google-api_core==1.31.1`.
diff --git a/SECURITY.md b/SECURITY.md
new file mode 100644
index 0000000..8b58ae9
--- /dev/null
+++ b/SECURITY.md
@@ -0,0 +1,7 @@
+# Security Policy
+
+To report a security issue, please use [g.co/vulnz](https://g.co/vulnz).
+
+The Google Security Team will respond within 5 working days of your report on g.co/vulnz.
+
+We use g.co/vulnz for our intake, and do coordination and disclosure here using GitHub Security Advisory to privately discuss and fix the issue.
diff --git a/docs/_static/custom.css b/docs/_static/custom.css
new file mode 100644
index 0000000..b0a2954
--- /dev/null
+++ b/docs/_static/custom.css
@@ -0,0 +1,20 @@
+div#python2-eol {
+	border-color: red;
+	border-width: medium;
+}
+
+/* Ensure minimum width for 'Parameters' / 'Returns' column */
+dl.field-list > dt {
+    min-width: 100px
+}
+
+/* Insert space between methods for readability */
+dl.method {
+	padding-top: 10px;
+	padding-bottom: 10px
+}
+
+/* Insert empty space between classes */
+dl.class {
+	padding-bottom: 50px
+}
diff --git a/docs/_templates/layout.html b/docs/_templates/layout.html
new file mode 100644
index 0000000..6316a53
--- /dev/null
+++ b/docs/_templates/layout.html
@@ -0,0 +1,50 @@
+
+{% extends "!layout.html" %}
+{%- block content %}
+{%- if theme_fixed_sidebar|lower == 'true' %}
+  <div class="document">
+    {{ sidebar() }}
+    {%- block document %}
+      <div class="documentwrapper">
+      {%- if render_sidebar %}
+        <div class="bodywrapper">
+      {%- endif %}
+
+          {%- block relbar_top %}
+            {%- if theme_show_relbar_top|tobool %}
+              <div class="related top">
+                &nbsp;
+                {{- rellink_markup () }}
+              </div>
+            {%- endif %}
+          {% endblock %}
+
+          <div class="body" role="main">
+          	<div class="admonition" id="python2-eol"> 
+          	 As of January 1, 2020 this library no longer supports Python 2 on the latest released version. 
+          	 Library versions released prior to that date will continue to be available. For more information please
+          	 visit <a href="https://cloud.google.com/python/docs/python2-sunset/">Python 2 support on Google Cloud</a>.
+          	</div>
+            {% block body %} {% endblock %}
+          </div>
+
+          {%- block relbar_bottom %}
+            {%- if theme_show_relbar_bottom|tobool %}
+              <div class="related bottom">
+                &nbsp;
+                {{- rellink_markup () }}
+              </div>
+            {%- endif %}
+          {% endblock %}
+
+      {%- if render_sidebar %}
+        </div>
+      {%- endif %}
+      </div>
+    {%- endblock %}
+    <div class="clearer"></div>
+  </div>
+{%- else %}
+{{ super() }}
+{%- endif %}
+{%- endblock %}
diff --git a/docs/auth.rst b/docs/auth.rst
new file mode 100644
index 0000000..a9b296d
--- /dev/null
+++ b/docs/auth.rst
@@ -0,0 +1,213 @@
+Authentication
+**************
+
+.. _Overview:
+
+Overview
+========
+
+For a language agnostic overview of authentication on Google Cloud, see `Authentication Overview`_.
+
+.. _Authentication Overview: https://cloud.google.com/docs/authentication
+
+*   **If you're running in a Google Virtual Machine Environment (Compute Engine, App Engine, Cloud Run, Cloud Functions)**,
+    authentication should "just work".
+
+*   **If you're developing locally**,
+    the easiest way to authenticate is using the `Google Cloud SDK`_:
+
+    .. code-block:: bash
+
+        $ gcloud auth application-default login
+
+    Note that this command generates credentials for client libraries. To authenticate the CLI itself, use:
+
+    .. code-block:: bash
+
+        $ gcloud auth login
+
+    Previously, ``gcloud auth login`` was used for both use cases. If
+    your ``gcloud`` installation does not support the new command,
+    please update it:
+
+    .. code-block:: bash
+
+        $ gcloud components update
+
+.. _Google Cloud SDK: http://cloud.google.com/sdk
+
+
+*   **If you're running your application elsewhere**,
+    you should download a `service account`_ JSON keyfile
+    and point to it using an environment variable:
+
+    .. code-block:: bash
+
+        $ export GOOGLE_APPLICATION_CREDENTIALS="/path/to/keyfile.json"
+
+.. _service account: https://cloud.google.com/iam/docs/creating-managing-service-accounts#creating
+
+Client-Provided Authentication
+==============================
+
+Every package uses a :class:`Client <google.cloud.client.Client>`
+as a base for interacting with an API.
+For example:
+
+.. code-block:: python
+
+    from google.cloud import datastore
+    client = datastore.Client()
+
+Passing no arguments at all will "just work" if you've followed the
+instructions in the :ref:`Overview`.
+The credentials are inferred from your local environment by using
+Google `Application Default Credentials`_.
+
+.. _Application Default Credentials: https://developers.google.com/identity/protocols/application-default-credentials
+
+.. _Precedence:
+
+Credential Discovery Precedence
+-------------------------------
+
+When loading the `Application Default Credentials`_,
+the library will check for credentials in your environment by following the
+precedence outlined by :func:`google.auth.default`.
+
+Explicit Credentials
+====================
+
+The Application Default Credentials discussed above can be useful
+if your code needs to run in many different environments or
+if you just don't want authentication to be a focus in your code.
+
+However, you may want to be explicit because
+
+* your code will only run in one place
+* you may have code which needs to be run as a specific service account
+  every time (rather than with the locally inferred credentials)
+* you may want to use two separate accounts to simultaneously access data
+  from different projects
+
+In these situations, you can create an explicit
+:class:`~google.auth.credentials.Credentials` object suited to your environment.
+After creation, you can pass it directly to a :class:`Client <google.cloud.client.Client>`:
+
+.. code:: python
+
+    client = Client(credentials=credentials)
+
+.. tip::
+    To create a credentials object, follow the `google-auth-guide`_.
+
+.. _google-auth-guide: https://googleapis.dev/python/google-auth/latest/user-guide.html#service-account-private-key-files
+
+Google Compute Engine Environment
+---------------------------------
+
+These credentials are used in Google Virtual Machine Environments.
+This includes most App Engine runtimes, Compute Engine, Cloud
+Functions, and Cloud Run.
+
+To create
+:class:`credentials <google.auth.compute_engine.Credentials>`:
+
+.. code:: python
+
+    from google.auth import compute_engine
+    credentials = compute_engine.Credentials()
+
+Service Accounts
+----------------
+
+A `service account`_ is stored in a JSON keyfile.
+
+.. code:: python
+
+    from google.oauth2 import service_account
+
+    credentials = service_account.Credentials.from_service_account_file(
+        '/path/to/key.json')
+
+A JSON string or dictionary:
+
+.. code:: python
+
+    import json
+
+    from google.oauth2 import service_account
+
+    json_account_info = json.loads(...)  # convert JSON to dictionary
+    credentials = service_account.Credentials.from_service_account_info(
+        json_account_info)
+
+.. tip::
+
+    Previously the Google Cloud Console would issue a PKCS12/P12 key for your
+    service account. This library does not support that key format. You can
+    generate a new JSON key for the same service account from the console.
+
+User Accounts (3-legged OAuth 2.0) with a refresh token
+-------------------------------------------------------
+
+The majority of cases are intended to authenticate machines or
+workers rather than actual user accounts. However, it's also
+possible to call Google Cloud APIs with a user account via
+`OAuth 2.0`_.
+
+.. _OAuth 2.0: https://developers.google.com/identity/protocols/OAuth2
+
+.. tip::
+
+    A production application should **use a service account**,
+    but you may wish to use your own personal user account when first
+    getting started with the ``google-cloud-*`` library.
+
+The simplest way to use credentials from a user account is via
+Application Default Credentials using ``gcloud auth login``
+(as mentioned above) and :func:`google.auth.default`:
+
+.. code:: python
+
+    import google.auth
+
+    credentials, project = google.auth.default()
+
+This will still follow the :ref:`precedence <Precedence>`
+described above,
+so be sure none of the other possible environments conflict
+with your user provided credentials.
+
+Troubleshooting
+===============
+
+Setting up a Service Account
+----------------------------
+
+If your application is not running on a Google Virtual Machine Environment,
+you need a Service Account. See `Creating a Service Account`_.
+
+.. _Creating a Service Account: https://cloud.google.com/iam/docs/creating-managing-service-accounts#creating
+
+Using Google Compute Engine
+---------------------------
+
+If your code is running on Google Compute Engine,
+using the inferred Google `Application Default Credentials`_
+will be sufficient for retrieving credentials.
+
+However, by default your credentials may not grant you
+access to the services you intend to use.
+Be sure when you `set up the GCE instance`_,
+you add the correct scopes for the APIs you want to access:
+
+* **All APIs**
+
+    * ``https://www.googleapis.com/auth/cloud-platform``
+    * ``https://www.googleapis.com/auth/cloud-platform.read-only``
+
+For scopes for specific APIs see `OAuth 2.0 Scopes for Google APIs`_
+
+.. _set up the GCE instance: https://cloud.google.com/compute/docs/authentication#using
+.. _OAuth 2.0 Scopes for Google APIS: https://developers.google.com/identity/protocols/oauth2/scopes
diff --git a/docs/changelog.md b/docs/changelog.md
new file mode 120000
index 0000000..04c99a5
--- /dev/null
+++ b/docs/changelog.md
@@ -0,0 +1 @@
+../CHANGELOG.md
\ No newline at end of file
diff --git a/docs/client_info.rst b/docs/client_info.rst
new file mode 100644
index 0000000..e976b18
--- /dev/null
+++ b/docs/client_info.rst
@@ -0,0 +1,11 @@
+Client Information Helpers
+==========================
+
+.. automodule:: google.api_core.client_info
+  :members:
+  :show-inheritance:
+
+.. automodule:: google.api_core.gapic_v1.client_info
+  :members:
+  :show-inheritance:
+
diff --git a/docs/client_options.rst b/docs/client_options.rst
new file mode 100644
index 0000000..da7c9a3
--- /dev/null
+++ b/docs/client_options.rst
@@ -0,0 +1,6 @@
+Client Options
+==========================
+
+.. automodule:: google.api_core.client_options
+  :members:
+  :show-inheritance:
diff --git a/docs/conf.py b/docs/conf.py
new file mode 100644
index 0000000..09f0c2b
--- /dev/null
+++ b/docs/conf.py
@@ -0,0 +1,375 @@
+# -*- coding: utf-8 -*-
+# Copyright 2021 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+# http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# google-api-core documentation build configuration file
+#
+# This file is execfile()d with the current directory set to its
+# containing dir.
+#
+# Note that not all possible configuration values are present in this
+# autogenerated file.
+#
+# All configuration values have a default; values that are commented out
+# serve to show the default.
+
+import sys
+import os
+import shlex
+
+# If extensions (or modules to document with autodoc) are in another directory,
+# add these directories to sys.path here. If the directory is relative to the
+# documentation root, use os.path.abspath to make it absolute, like shown here.
+sys.path.insert(0, os.path.abspath(".."))
+
+# For plugins that can not read conf.py.
+# See also: https://github.com/docascode/sphinx-docfx-yaml/issues/85
+sys.path.insert(0, os.path.abspath("."))
+
+__version__ = ""
+
+# -- General configuration ------------------------------------------------
+
+# If your documentation needs a minimal Sphinx version, state it here.
+needs_sphinx = "1.5.5"
+
+# Add any Sphinx extension module names here, as strings. They can be
+# extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
+# ones.
+extensions = [
+    "sphinx.ext.autodoc",
+    "sphinx.ext.autosummary",
+    "sphinx.ext.intersphinx",
+    "sphinx.ext.coverage",
+    "sphinx.ext.doctest",
+    "sphinx.ext.napoleon",
+    "sphinx.ext.todo",
+    "sphinx.ext.viewcode",
+    "recommonmark",
+]
+
+# autodoc/autosummary flags
+autoclass_content = "both"
+autodoc_default_options = {"members": True}
+autosummary_generate = True
+
+
+# Add any paths that contain templates here, relative to this directory.
+templates_path = ["_templates"]
+
+# The suffix(es) of source filenames.
+# You can specify multiple suffix as a list of string:
+# source_suffix = ['.rst', '.md']
+source_suffix = [".rst", ".md"]
+
+# The encoding of source files.
+# source_encoding = 'utf-8-sig'
+
+# The root toctree document.
+root_doc = "index"
+
+# General information about the project.
+project = "google-api-core"
+copyright = "2019, Google"
+author = "Google APIs"
+
+# The version info for the project you're documenting, acts as replacement for
+# |version| and |release|, also used in various other places throughout the
+# built documents.
+#
+# The full version, including alpha/beta/rc tags.
+release = __version__
+# The short X.Y version.
+version = ".".join(release.split(".")[0:2])
+
+# The language for content autogenerated by Sphinx. Refer to documentation
+# for a list of supported languages.
+#
+# This is also used if you do content translation via gettext catalogs.
+# Usually you set "language" from the command line for these cases.
+language = None
+
+# There are two options for replacing |today|: either, you set today to some
+# non-false value, then it is used:
+# today = ''
+# Else, today_fmt is used as the format for a strftime call.
+# today_fmt = '%B %d, %Y'
+
+# List of patterns, relative to source directory, that match files and
+# directories to ignore when looking for source files.
+exclude_patterns = [
+    "_build",
+    "**/.nox/**/*",
+    "samples/AUTHORING_GUIDE.md",
+    "samples/CONTRIBUTING.md",
+    "samples/snippets/README.rst",
+]
+
+# The reST default role (used for this markup: `text`) to use for all
+# documents.
+# default_role = None
+
+# If true, '()' will be appended to :func: etc. cross-reference text.
+# add_function_parentheses = True
+
+# If true, the current module name will be prepended to all description
+# unit titles (such as .. function::).
+# add_module_names = True
+
+# If true, sectionauthor and moduleauthor directives will be shown in the
+# output. They are ignored by default.
+# show_authors = False
+
+# The name of the Pygments (syntax highlighting) style to use.
+pygments_style = "sphinx"
+
+# A list of ignored prefixes for module index sorting.
+# modindex_common_prefix = []
+
+# If true, keep warnings as "system message" paragraphs in the built documents.
+# keep_warnings = False
+
+# If true, `todo` and `todoList` produce output, else they produce nothing.
+todo_include_todos = True
+
+
+# -- Options for HTML output ----------------------------------------------
+
+# The theme to use for HTML and HTML Help pages.  See the documentation for
+# a list of builtin themes.
+html_theme = "alabaster"
+
+# Theme options are theme-specific and customize the look and feel of a theme
+# further.  For a list of options available for each theme, see the
+# documentation.
+html_theme_options = {
+    "description": "Google Cloud Client Libraries for google-api-core",
+    "github_user": "googleapis",
+    "github_repo": "python-api-core",
+    "github_banner": True,
+    "font_family": "'Roboto', Georgia, sans",
+    "head_font_family": "'Roboto', Georgia, serif",
+    "code_font_family": "'Roboto Mono', 'Consolas', monospace",
+}
+
+# Add any paths that contain custom themes here, relative to this directory.
+# html_theme_path = []
+
+# The name for this set of Sphinx documents.  If None, it defaults to
+# "<project> v<release> documentation".
+# html_title = None
+
+# A shorter title for the navigation bar.  Default is the same as html_title.
+# html_short_title = None
+
+# The name of an image file (relative to this directory) to place at the top
+# of the sidebar.
+# html_logo = None
+
+# The name of an image file (within the static path) to use as favicon of the
+# docs.  This file should be a Windows icon file (.ico) being 16x16 or 32x32
+# pixels large.
+# html_favicon = None
+
+# Add any paths that contain custom static files (such as style sheets) here,
+# relative to this directory. They are copied after the builtin static files,
+# so a file named "default.css" will overwrite the builtin "default.css".
+html_static_path = ["_static"]
+
+# Add any extra paths that contain custom files (such as robots.txt or
+# .htaccess) here, relative to this directory. These files are copied
+# directly to the root of the documentation.
+# html_extra_path = []
+
+# If not '', a 'Last updated on:' timestamp is inserted at every page bottom,
+# using the given strftime format.
+# html_last_updated_fmt = '%b %d, %Y'
+
+# If true, SmartyPants will be used to convert quotes and dashes to
+# typographically correct entities.
+# html_use_smartypants = True
+
+# Custom sidebar templates, maps document names to template names.
+# html_sidebars = {}
+
+# Additional templates that should be rendered to pages, maps page names to
+# template names.
+# html_additional_pages = {}
+
+# If false, no module index is generated.
+# html_domain_indices = True
+
+# If false, no index is generated.
+# html_use_index = True
+
+# If true, the index is split into individual pages for each letter.
+# html_split_index = False
+
+# If true, links to the reST sources are added to the pages.
+# html_show_sourcelink = True
+
+# If true, "Created using Sphinx" is shown in the HTML footer. Default is True.
+# html_show_sphinx = True
+
+# If true, "(C) Copyright ..." is shown in the HTML footer. Default is True.
+# html_show_copyright = True
+
+# If true, an OpenSearch description file will be output, and all pages will
+# contain a <link> tag referring to it.  The value of this option must be the
+# base URL from which the finished HTML is served.
+# html_use_opensearch = ''
+
+# This is the file name suffix for HTML files (e.g. ".xhtml").
+# html_file_suffix = None
+
+# Language to be used for generating the HTML full-text search index.
+# Sphinx supports the following languages:
+#   'da', 'de', 'en', 'es', 'fi', 'fr', 'hu', 'it', 'ja'
+#   'nl', 'no', 'pt', 'ro', 'ru', 'sv', 'tr'
+# html_search_language = 'en'
+
+# A dictionary with options for the search language support, empty by default.
+# Now only 'ja' uses this config value
+# html_search_options = {'type': 'default'}
+
+# The name of a javascript file (relative to the configuration directory) that
+# implements a search results scorer. If empty, the default will be used.
+# html_search_scorer = 'scorer.js'
+
+# Output file base name for HTML help builder.
+htmlhelp_basename = "google-api-core-doc"
+
+# -- Options for warnings ------------------------------------------------------
+
+
+suppress_warnings = [
+    # Temporarily suppress this to avoid "more than one target found for
+    # cross-reference" warning, which are intractable for us to avoid while in
+    # a mono-repo.
+    # See https://github.com/sphinx-doc/sphinx/blob
+    # /2a65ffeef5c107c19084fabdd706cdff3f52d93c/sphinx/domains/python.py#L843
+    "ref.python"
+]
+
+# -- Options for LaTeX output ---------------------------------------------
+
+latex_elements = {
+    # The paper size ('letterpaper' or 'a4paper').
+    #'papersize': 'letterpaper',
+    # The font size ('10pt', '11pt' or '12pt').
+    #'pointsize': '10pt',
+    # Additional stuff for the LaTeX preamble.
+    #'preamble': '',
+    # Latex figure (float) alignment
+    #'figure_align': 'htbp',
+}
+
+# Grouping the document tree into LaTeX files. List of tuples
+# (source start file, target name, title,
+#  author, documentclass [howto, manual, or own class]).
+latex_documents = [
+    (
+        root_doc,
+        "google-api-core.tex",
+        "google-api-core Documentation",
+        author,
+        "manual",
+    )
+]
+
+# The name of an image file (relative to this directory) to place at the top of
+# the title page.
+# latex_logo = None
+
+# For "manual" documents, if this is true, then toplevel headings are parts,
+# not chapters.
+# latex_use_parts = False
+
+# If true, show page references after internal links.
+# latex_show_pagerefs = False
+
+# If true, show URL addresses after external links.
+# latex_show_urls = False
+
+# Documents to append as an appendix to all manuals.
+# latex_appendices = []
+
+# If false, no module index is generated.
+# latex_domain_indices = True
+
+
+# -- Options for manual page output ---------------------------------------
+
+# One entry per manual page. List of tuples
+# (source start file, name, description, authors, manual section).
+man_pages = [
+    (root_doc, "google-api-core", "google-api-core Documentation", [author], 1,)
+]
+
+# If true, show URL addresses after external links.
+# man_show_urls = False
+
+
+# -- Options for Texinfo output -------------------------------------------
+
+# Grouping the document tree into Texinfo files. List of tuples
+# (source start file, target name, title, author,
+#  dir menu entry, description, category)
+texinfo_documents = [
+    (
+        root_doc,
+        "google-api-core",
+        "google-api-core Documentation",
+        author,
+        "google-api-core",
+        "google-api-core Library",
+        "APIs",
+    )
+]
+
+# Documents to append as an appendix to all manuals.
+# texinfo_appendices = []
+
+# If false, no module index is generated.
+# texinfo_domain_indices = True
+
+# How to display URL addresses: 'footnote', 'no', or 'inline'.
+# texinfo_show_urls = 'footnote'
+
+# If true, do not generate a @detailmenu in the "Top" node's menu.
+# texinfo_no_detailmenu = False
+
+
+# Example configuration for intersphinx: refer to the Python standard library.
+intersphinx_mapping = {
+    "python": ("https://python.readthedocs.org/en/latest/", None),
+    "google-auth": ("https://googleapis.dev/python/google-auth/latest/", None),
+    "google.api_core": ("https://googleapis.dev/python/google-api-core/latest/", None,),
+    "grpc": ("https://grpc.github.io/grpc/python/", None),
+    "proto-plus": ("https://proto-plus-python.readthedocs.io/en/latest/", None),
+    "protobuf": ("https://googleapis.dev/python/protobuf/latest/", None),
+}
+
+
+# Napoleon settings
+napoleon_google_docstring = True
+napoleon_numpy_docstring = True
+napoleon_include_private_with_doc = False
+napoleon_include_special_with_doc = True
+napoleon_use_admonition_for_examples = False
+napoleon_use_admonition_for_notes = False
+napoleon_use_admonition_for_references = False
+napoleon_use_ivar = False
+napoleon_use_param = True
+napoleon_use_rtype = True
diff --git a/docs/exceptions.rst b/docs/exceptions.rst
new file mode 100644
index 0000000..d671f4e
--- /dev/null
+++ b/docs/exceptions.rst
@@ -0,0 +1,6 @@
+Exceptions
+==========
+
+.. automodule:: google.api_core.exceptions
+  :members:
+  :show-inheritance:
diff --git a/docs/futures.rst b/docs/futures.rst
new file mode 100644
index 0000000..d0dadac
--- /dev/null
+++ b/docs/futures.rst
@@ -0,0 +1,14 @@
+Futures
+=======================
+
+.. automodule:: google.api_core.future
+  :members:
+  :show-inheritance:
+
+.. automodule:: google.api_core.future.polling
+  :members:
+  :show-inheritance:
+
+.. automodule:: google.api_core.future.async_future
+  :members:
+  :show-inheritance:
diff --git a/docs/helpers.rst b/docs/helpers.rst
new file mode 100644
index 0000000..6f72df9
--- /dev/null
+++ b/docs/helpers.rst
@@ -0,0 +1,26 @@
+Helpers
+=======
+
+
+General Helpers
+---------------
+
+.. automodule:: google.api_core.general_helpers
+  :members:
+  :show-inheritance:
+
+
+Datetime Helpers
+----------------
+
+.. automodule:: google.api_core.datetime_helpers
+  :members:
+  :show-inheritance:
+
+
+gRPC Helpers
+------------
+
+.. automodule:: google.api_core.grpc_helpers
+  :members:
+  :show-inheritance:
diff --git a/docs/iam.rst b/docs/iam.rst
new file mode 100644
index 0000000..bb80ae3
--- /dev/null
+++ b/docs/iam.rst
@@ -0,0 +1,7 @@
+Identity and Access Management
+==============================
+
+.. automodule:: google.api_core.iam
+  :members:
+  :show-inheritance:
+  :member-order: bysource
diff --git a/docs/index.rst b/docs/index.rst
new file mode 100644
index 0000000..858e889
--- /dev/null
+++ b/docs/index.rst
@@ -0,0 +1,32 @@
+The ``google-cloud-core`` package contains helpers common to all
+``google-cloud-*`` packages. In an attempt to reach a stable API,
+much of the functionality has been split out into this package,
+``google-api-core``.
+
+.. include:: multiprocessing.rst
+
+Core
+====
+
+.. toctree::
+    auth
+    client_info
+    client_options
+    exceptions
+    futures
+    helpers
+    iam
+    operation
+    operations_client
+    page_iterator
+    path_template
+    retry
+    timeout
+
+Changelog
+~~~~~~~~~
+
+.. toctree::
+    :maxdepth: 2
+
+    changelog
diff --git a/docs/multiprocessing.rst b/docs/multiprocessing.rst
new file mode 100644
index 0000000..536d17b
--- /dev/null
+++ b/docs/multiprocessing.rst
@@ -0,0 +1,7 @@
+.. note::
+
+   Because this client uses :mod:`grpc` library, it is safe to
+   share instances across threads. In multiprocessing scenarios, the best
+   practice is to create client instances *after* the invocation of
+   :func:`os.fork` by :class:`multiprocessing.pool.Pool` or
+   :class:`multiprocessing.Process`.
diff --git a/docs/operation.rst b/docs/operation.rst
new file mode 100644
index 0000000..492cf67
--- /dev/null
+++ b/docs/operation.rst
@@ -0,0 +1,13 @@
+Long-Running Operations
+=======================
+
+.. automodule:: google.api_core.operation
+  :members:
+  :show-inheritance:
+
+Long-Running Operations in AsyncIO
+-------------------------------------
+
+.. automodule:: google.api_core.operation_async
+  :members:
+  :show-inheritance:
diff --git a/docs/operations_client.rst b/docs/operations_client.rst
new file mode 100644
index 0000000..be466d3
--- /dev/null
+++ b/docs/operations_client.rst
@@ -0,0 +1,6 @@
+Long-Running Operations Client
+==============================
+
+.. automodule:: google.api_core.operations_v1
+  :members:
+  :show-inheritance:
diff --git a/docs/page_iterator.rst b/docs/page_iterator.rst
new file mode 100644
index 0000000..3652e6d
--- /dev/null
+++ b/docs/page_iterator.rst
@@ -0,0 +1,13 @@
+Page Iterators
+==============
+
+.. automodule:: google.api_core.page_iterator
+  :members:
+  :show-inheritance:
+
+Page Iterators in AsyncIO
+-------------------------
+
+.. automodule:: google.api_core.page_iterator_async
+  :members:
+  :show-inheritance:
diff --git a/docs/path_template.rst b/docs/path_template.rst
new file mode 100644
index 0000000..220779e
--- /dev/null
+++ b/docs/path_template.rst
@@ -0,0 +1,6 @@
+Path Templates
+==============
+
+.. automodule:: google.api_core.path_template
+  :members:
+  :show-inheritance:
diff --git a/docs/retry.rst b/docs/retry.rst
new file mode 100644
index 0000000..97a7f2c
--- /dev/null
+++ b/docs/retry.rst
@@ -0,0 +1,13 @@
+Retry
+=====
+
+.. automodule:: google.api_core.retry
+  :members:
+  :show-inheritance:
+
+Retry in AsyncIO
+----------------
+
+.. automodule:: google.api_core.retry_async
+  :members:
+  :show-inheritance:
diff --git a/docs/timeout.rst b/docs/timeout.rst
new file mode 100644
index 0000000..943d425
--- /dev/null
+++ b/docs/timeout.rst
@@ -0,0 +1,6 @@
+Timeout
+=======
+
+.. automodule:: google.api_core.timeout
+  :members:
+  :show-inheritance:
diff --git a/google/__init__.py b/google/__init__.py
new file mode 100644
index 0000000..9f1d549
--- /dev/null
+++ b/google/__init__.py
@@ -0,0 +1,25 @@
+# Copyright 2016 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Google namespace package."""
+
+try:
+    import pkg_resources
+
+    pkg_resources.declare_namespace(__name__)
+except ImportError:
+    import pkgutil
+
+    # See: https://github.com/python/mypy/issues/1422
+    __path__ = pkgutil.extend_path(__path__, __name__)  # type: ignore
diff --git a/google/api_core/__init__.py b/google/api_core/__init__.py
new file mode 100644
index 0000000..605dd8b
--- /dev/null
+++ b/google/api_core/__init__.py
@@ -0,0 +1,22 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Google API Core.
+
+This package contains common code and utilties used by Google client libraries.
+"""
+
+from google.api_core import version as api_core_version
+
+__version__ = api_core_version.__version__
diff --git a/google/api_core/bidi.py b/google/api_core/bidi.py
new file mode 100644
index 0000000..4b4963f
--- /dev/null
+++ b/google/api_core/bidi.py
@@ -0,0 +1,735 @@
+# Copyright 2017, Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Bi-directional streaming RPC helpers."""
+
+import collections
+import datetime
+import logging
+import queue as queue_module
+import threading
+import time
+
+from google.api_core import exceptions
+
+_LOGGER = logging.getLogger(__name__)
+_BIDIRECTIONAL_CONSUMER_NAME = "Thread-ConsumeBidirectionalStream"
+
+
+class _RequestQueueGenerator(object):
+    """A helper for sending requests to a gRPC stream from a Queue.
+
+    This generator takes requests off a given queue and yields them to gRPC.
+
+    This helper is useful when you have an indeterminate, indefinite, or
+    otherwise open-ended set of requests to send through a request-streaming
+    (or bidirectional) RPC.
+
+    The reason this is necessary is because gRPC takes an iterator as the
+    request for request-streaming RPCs. gRPC consumes this iterator in another
+    thread to allow it to block while generating requests for the stream.
+    However, if the generator blocks indefinitely gRPC will not be able to
+    clean up the thread as it'll be blocked on `next(iterator)` and not be able
+    to check the channel status to stop iterating. This helper mitigates that
+    by waiting on the queue with a timeout and checking the RPC state before
+    yielding.
+
+    Finally, it allows for retrying without swapping queues because if it does
+    pull an item off the queue when the RPC is inactive, it'll immediately put
+    it back and then exit. This is necessary because yielding the item in this
+    case will cause gRPC to discard it. In practice, this means that the order
+    of messages is not guaranteed. If such a thing is necessary it would be
+    easy to use a priority queue.
+
+    Example::
+
+        requests = request_queue_generator(q)
+        call = stub.StreamingRequest(iter(requests))
+        requests.call = call
+
+        for response in call:
+            print(response)
+            q.put(...)
+
+    Note that it is possible to accomplish this behavior without "spinning"
+    (using a queue timeout). One possible way would be to use more threads to
+    multiplex the grpc end event with the queue, another possible way is to
+    use selectors and a custom event/queue object. Both of these approaches
+    are significant from an engineering perspective for small benefit - the
+    CPU consumed by spinning is pretty minuscule.
+
+    Args:
+        queue (queue_module.Queue): The request queue.
+        period (float): The number of seconds to wait for items from the queue
+            before checking if the RPC is cancelled. In practice, this
+            determines the maximum amount of time the request consumption
+            thread will live after the RPC is cancelled.
+        initial_request (Union[protobuf.Message,
+                Callable[None, protobuf.Message]]): The initial request to
+            yield. This is done independently of the request queue to allow fo
+            easily restarting streams that require some initial configuration
+            request.
+    """
+
+    def __init__(self, queue, period=1, initial_request=None):
+        self._queue = queue
+        self._period = period
+        self._initial_request = initial_request
+        self.call = None
+
+    def _is_active(self):
+        # Note: there is a possibility that this starts *before* the call
+        # property is set. So we have to check if self.call is set before
+        # seeing if it's active.
+        if self.call is not None and not self.call.is_active():
+            return False
+        else:
+            return True
+
+    def __iter__(self):
+        if self._initial_request is not None:
+            if callable(self._initial_request):
+                yield self._initial_request()
+            else:
+                yield self._initial_request
+
+        while True:
+            try:
+                item = self._queue.get(timeout=self._period)
+            except queue_module.Empty:
+                if not self._is_active():
+                    _LOGGER.debug(
+                        "Empty queue and inactive call, exiting request " "generator."
+                    )
+                    return
+                else:
+                    # call is still active, keep waiting for queue items.
+                    continue
+
+            # The consumer explicitly sent "None", indicating that the request
+            # should end.
+            if item is None:
+                _LOGGER.debug("Cleanly exiting request generator.")
+                return
+
+            if not self._is_active():
+                # We have an item, but the call is closed. We should put the
+                # item back on the queue so that the next call can consume it.
+                self._queue.put(item)
+                _LOGGER.debug(
+                    "Inactive call, replacing item on queue and exiting "
+                    "request generator."
+                )
+                return
+
+            yield item
+
+
+class _Throttle(object):
+    """A context manager limiting the total entries in a sliding time window.
+
+    If more than ``access_limit`` attempts are made to enter the context manager
+    instance in the last ``time window`` interval, the exceeding requests block
+    until enough time elapses.
+
+    The context manager instances are thread-safe and can be shared between
+    multiple threads. If multiple requests are blocked and waiting to enter,
+    the exact order in which they are allowed to proceed is not determined.
+
+    Example::
+
+        max_three_per_second = _Throttle(
+            access_limit=3, time_window=datetime.timedelta(seconds=1)
+        )
+
+        for i in range(5):
+            with max_three_per_second as time_waited:
+                print("{}: Waited {} seconds to enter".format(i, time_waited))
+
+    Args:
+        access_limit (int): the maximum number of entries allowed in the time window
+        time_window (datetime.timedelta): the width of the sliding time window
+    """
+
+    def __init__(self, access_limit, time_window):
+        if access_limit < 1:
+            raise ValueError("access_limit argument must be positive")
+
+        if time_window <= datetime.timedelta(0):
+            raise ValueError("time_window argument must be a positive timedelta")
+
+        self._time_window = time_window
+        self._access_limit = access_limit
+        self._past_entries = collections.deque(
+            maxlen=access_limit
+        )  # least recent first
+        self._entry_lock = threading.Lock()
+
+    def __enter__(self):
+        with self._entry_lock:
+            cutoff_time = datetime.datetime.now() - self._time_window
+
+            # drop the entries that are too old, as they are no longer relevant
+            while self._past_entries and self._past_entries[0] < cutoff_time:
+                self._past_entries.popleft()
+
+            if len(self._past_entries) < self._access_limit:
+                self._past_entries.append(datetime.datetime.now())
+                return 0.0  # no waiting was needed
+
+            to_wait = (self._past_entries[0] - cutoff_time).total_seconds()
+            time.sleep(to_wait)
+
+            self._past_entries.append(datetime.datetime.now())
+            return to_wait
+
+    def __exit__(self, *_):
+        pass
+
+    def __repr__(self):
+        return "{}(access_limit={}, time_window={})".format(
+            self.__class__.__name__, self._access_limit, repr(self._time_window)
+        )
+
+
+class BidiRpc(object):
+    """A helper for consuming a bi-directional streaming RPC.
+
+    This maps gRPC's built-in interface which uses a request iterator and a
+    response iterator into a socket-like :func:`send` and :func:`recv`. This
+    is a more useful pattern for long-running or asymmetric streams (streams
+    where there is not a direct correlation between the requests and
+    responses).
+
+    Example::
+
+        initial_request = example_pb2.StreamingRpcRequest(
+            setting='example')
+        rpc = BidiRpc(
+            stub.StreamingRpc,
+            initial_request=initial_request,
+            metadata=[('name', 'value')]
+        )
+
+        rpc.open()
+
+        while rpc.is_active():
+            print(rpc.recv())
+            rpc.send(example_pb2.StreamingRpcRequest(
+                data='example'))
+
+    This does *not* retry the stream on errors. See :class:`ResumableBidiRpc`.
+
+    Args:
+        start_rpc (grpc.StreamStreamMultiCallable): The gRPC method used to
+            start the RPC.
+        initial_request (Union[protobuf.Message,
+                Callable[None, protobuf.Message]]): The initial request to
+            yield. This is useful if an initial request is needed to start the
+            stream.
+        metadata (Sequence[Tuple(str, str)]): RPC metadata to include in
+            the request.
+    """
+
+    def __init__(self, start_rpc, initial_request=None, metadata=None):
+        self._start_rpc = start_rpc
+        self._initial_request = initial_request
+        self._rpc_metadata = metadata
+        self._request_queue = queue_module.Queue()
+        self._request_generator = None
+        self._is_active = False
+        self._callbacks = []
+        self.call = None
+
+    def add_done_callback(self, callback):
+        """Adds a callback that will be called when the RPC terminates.
+
+        This occurs when the RPC errors or is successfully terminated.
+
+        Args:
+            callback (Callable[[grpc.Future], None]): The callback to execute.
+                It will be provided with the same gRPC future as the underlying
+                stream which will also be a :class:`grpc.Call`.
+        """
+        self._callbacks.append(callback)
+
+    def _on_call_done(self, future):
+        for callback in self._callbacks:
+            callback(future)
+
+    def open(self):
+        """Opens the stream."""
+        if self.is_active:
+            raise ValueError("Can not open an already open stream.")
+
+        request_generator = _RequestQueueGenerator(
+            self._request_queue, initial_request=self._initial_request
+        )
+        call = self._start_rpc(iter(request_generator), metadata=self._rpc_metadata)
+
+        request_generator.call = call
+
+        # TODO: api_core should expose the future interface for wrapped
+        # callables as well.
+        if hasattr(call, "_wrapped"):  # pragma: NO COVER
+            call._wrapped.add_done_callback(self._on_call_done)
+        else:
+            call.add_done_callback(self._on_call_done)
+
+        self._request_generator = request_generator
+        self.call = call
+
+    def close(self):
+        """Closes the stream."""
+        if self.call is None:
+            return
+
+        self._request_queue.put(None)
+        self.call.cancel()
+        self._request_generator = None
+        # Don't set self.call to None. Keep it around so that send/recv can
+        # raise the error.
+
+    def send(self, request):
+        """Queue a message to be sent on the stream.
+
+        Send is non-blocking.
+
+        If the underlying RPC has been closed, this will raise.
+
+        Args:
+            request (protobuf.Message): The request to send.
+        """
+        if self.call is None:
+            raise ValueError("Can not send() on an RPC that has never been open()ed.")
+
+        # Don't use self.is_active(), as ResumableBidiRpc will overload it
+        # to mean something semantically different.
+        if self.call.is_active():
+            self._request_queue.put(request)
+        else:
+            # calling next should cause the call to raise.
+            next(self.call)
+
+    def recv(self):
+        """Wait for a message to be returned from the stream.
+
+        Recv is blocking.
+
+        If the underlying RPC has been closed, this will raise.
+
+        Returns:
+            protobuf.Message: The received message.
+        """
+        if self.call is None:
+            raise ValueError("Can not recv() on an RPC that has never been open()ed.")
+
+        return next(self.call)
+
+    @property
+    def is_active(self):
+        """bool: True if this stream is currently open and active."""
+        return self.call is not None and self.call.is_active()
+
+    @property
+    def pending_requests(self):
+        """int: Returns an estimate of the number of queued requests."""
+        return self._request_queue.qsize()
+
+
+def _never_terminate(future_or_error):
+    """By default, no errors cause BiDi termination."""
+    return False
+
+
+class ResumableBidiRpc(BidiRpc):
+    """A :class:`BidiRpc` that can automatically resume the stream on errors.
+
+    It uses the ``should_recover`` arg to determine if it should re-establish
+    the stream on error.
+
+    Example::
+
+        def should_recover(exc):
+            return (
+                isinstance(exc, grpc.RpcError) and
+                exc.code() == grpc.StatusCode.UNVAILABLE)
+
+        initial_request = example_pb2.StreamingRpcRequest(
+            setting='example')
+
+        metadata = [('header_name', 'value')]
+
+        rpc = ResumableBidiRpc(
+            stub.StreamingRpc,
+            should_recover=should_recover,
+            initial_request=initial_request,
+            metadata=metadata
+        )
+
+        rpc.open()
+
+        while rpc.is_active():
+            print(rpc.recv())
+            rpc.send(example_pb2.StreamingRpcRequest(
+                data='example'))
+
+    Args:
+        start_rpc (grpc.StreamStreamMultiCallable): The gRPC method used to
+            start the RPC.
+        initial_request (Union[protobuf.Message,
+                Callable[None, protobuf.Message]]): The initial request to
+            yield. This is useful if an initial request is needed to start the
+            stream.
+        should_recover (Callable[[Exception], bool]): A function that returns
+            True if the stream should be recovered. This will be called
+            whenever an error is encountered on the stream.
+        should_terminate (Callable[[Exception], bool]): A function that returns
+            True if the stream should be terminated. This will be called
+            whenever an error is encountered on the stream.
+        metadata Sequence[Tuple(str, str)]: RPC metadata to include in
+            the request.
+        throttle_reopen (bool): If ``True``, throttling will be applied to
+            stream reopen calls. Defaults to ``False``.
+    """
+
+    def __init__(
+        self,
+        start_rpc,
+        should_recover,
+        should_terminate=_never_terminate,
+        initial_request=None,
+        metadata=None,
+        throttle_reopen=False,
+    ):
+        super(ResumableBidiRpc, self).__init__(start_rpc, initial_request, metadata)
+        self._should_recover = should_recover
+        self._should_terminate = should_terminate
+        self._operational_lock = threading.RLock()
+        self._finalized = False
+        self._finalize_lock = threading.Lock()
+
+        if throttle_reopen:
+            self._reopen_throttle = _Throttle(
+                access_limit=5, time_window=datetime.timedelta(seconds=10)
+            )
+        else:
+            self._reopen_throttle = None
+
+    def _finalize(self, result):
+        with self._finalize_lock:
+            if self._finalized:
+                return
+
+            for callback in self._callbacks:
+                callback(result)
+
+            self._finalized = True
+
+    def _on_call_done(self, future):
+        # Unlike the base class, we only execute the callbacks on a terminal
+        # error, not for errors that we can recover from. Note that grpc's
+        # "future" here is also a grpc.RpcError.
+        with self._operational_lock:
+            if self._should_terminate(future):
+                self._finalize(future)
+            elif not self._should_recover(future):
+                self._finalize(future)
+            else:
+                _LOGGER.debug("Re-opening stream from gRPC callback.")
+                self._reopen()
+
+    def _reopen(self):
+        with self._operational_lock:
+            # Another thread already managed to re-open this stream.
+            if self.call is not None and self.call.is_active():
+                _LOGGER.debug("Stream was already re-established.")
+                return
+
+            self.call = None
+            # Request generator should exit cleanly since the RPC its bound to
+            # has exited.
+            self._request_generator = None
+
+            # Note: we do not currently do any sort of backoff here. The
+            # assumption is that re-establishing the stream under normal
+            # circumstances will happen in intervals greater than 60s.
+            # However, it is possible in a degenerative case that the server
+            # closes the stream rapidly which would lead to thrashing here,
+            # but hopefully in those cases the server would return a non-
+            # retryable error.
+
+            try:
+                if self._reopen_throttle:
+                    with self._reopen_throttle:
+                        self.open()
+                else:
+                    self.open()
+            # If re-opening or re-calling the method fails for any reason,
+            # consider it a terminal error and finalize the stream.
+            except Exception as exc:
+                _LOGGER.debug("Failed to re-open stream due to %s", exc)
+                self._finalize(exc)
+                raise
+
+            _LOGGER.info("Re-established stream")
+
+    def _recoverable(self, method, *args, **kwargs):
+        """Wraps a method to recover the stream and retry on error.
+
+        If a retryable error occurs while making the call, then the stream will
+        be re-opened and the method will be retried. This happens indefinitely
+        so long as the error is a retryable one. If an error occurs while
+        re-opening the stream, then this method will raise immediately and
+        trigger finalization of this object.
+
+        Args:
+            method (Callable[..., Any]): The method to call.
+            args: The args to pass to the method.
+            kwargs: The kwargs to pass to the method.
+        """
+        while True:
+            try:
+                return method(*args, **kwargs)
+
+            except Exception as exc:
+                with self._operational_lock:
+                    _LOGGER.debug("Call to retryable %r caused %s.", method, exc)
+
+                    if self._should_terminate(exc):
+                        self.close()
+                        _LOGGER.debug("Terminating %r due to %s.", method, exc)
+                        self._finalize(exc)
+                        break
+
+                    if not self._should_recover(exc):
+                        self.close()
+                        _LOGGER.debug("Not retrying %r due to %s.", method, exc)
+                        self._finalize(exc)
+                        raise exc
+
+                    _LOGGER.debug("Re-opening stream from retryable %r.", method)
+                    self._reopen()
+
+    def _send(self, request):
+        # Grab a reference to the RPC call. Because another thread (notably
+        # the gRPC error thread) can modify self.call (by invoking reopen),
+        # we should ensure our reference can not change underneath us.
+        # If self.call is modified (such as replaced with a new RPC call) then
+        # this will use the "old" RPC, which should result in the same
+        # exception passed into gRPC's error handler being raised here, which
+        # will be handled by the usual error handling in retryable.
+        with self._operational_lock:
+            call = self.call
+
+        if call is None:
+            raise ValueError("Can not send() on an RPC that has never been open()ed.")
+
+        # Don't use self.is_active(), as ResumableBidiRpc will overload it
+        # to mean something semantically different.
+        if call.is_active():
+            self._request_queue.put(request)
+            pass
+        else:
+            # calling next should cause the call to raise.
+            next(call)
+
+    def send(self, request):
+        return self._recoverable(self._send, request)
+
+    def _recv(self):
+        with self._operational_lock:
+            call = self.call
+
+        if call is None:
+            raise ValueError("Can not recv() on an RPC that has never been open()ed.")
+
+        return next(call)
+
+    def recv(self):
+        return self._recoverable(self._recv)
+
+    def close(self):
+        self._finalize(None)
+        super(ResumableBidiRpc, self).close()
+
+    @property
+    def is_active(self):
+        """bool: True if this stream is currently open and active."""
+        # Use the operational lock. It's entirely possible for something
+        # to check the active state *while* the RPC is being retried.
+        # Also, use finalized to track the actual terminal state here.
+        # This is because if the stream is re-established by the gRPC thread
+        # it's technically possible to check this between when gRPC marks the
+        # RPC as inactive and when gRPC executes our callback that re-opens
+        # the stream.
+        with self._operational_lock:
+            return self.call is not None and not self._finalized
+
+
+class BackgroundConsumer(object):
+    """A bi-directional stream consumer that runs in a separate thread.
+
+    This maps the consumption of a stream into a callback-based model. It also
+    provides :func:`pause` and :func:`resume` to allow for flow-control.
+
+    Example::
+
+        def should_recover(exc):
+            return (
+                isinstance(exc, grpc.RpcError) and
+                exc.code() == grpc.StatusCode.UNVAILABLE)
+
+        initial_request = example_pb2.StreamingRpcRequest(
+            setting='example')
+
+        rpc = ResumeableBidiRpc(
+            stub.StreamingRpc,
+            initial_request=initial_request,
+            should_recover=should_recover)
+
+        def on_response(response):
+            print(response)
+
+        consumer = BackgroundConsumer(rpc, on_response)
+        consumer.start()
+
+    Note that error handling *must* be done by using the provided
+    ``bidi_rpc``'s ``add_done_callback``. This helper will automatically exit
+    whenever the RPC itself exits and will not provide any error details.
+
+    Args:
+        bidi_rpc (BidiRpc): The RPC to consume. Should not have been
+            ``open()``ed yet.
+        on_response (Callable[[protobuf.Message], None]): The callback to
+            be called for every response on the stream.
+    """
+
+    def __init__(self, bidi_rpc, on_response):
+        self._bidi_rpc = bidi_rpc
+        self._on_response = on_response
+        self._paused = False
+        self._wake = threading.Condition()
+        self._thread = None
+        self._operational_lock = threading.Lock()
+
+    def _on_call_done(self, future):
+        # Resume the thread if it's paused, this prevents blocking forever
+        # when the RPC has terminated.
+        self.resume()
+
+    def _thread_main(self, ready):
+        try:
+            ready.set()
+            self._bidi_rpc.add_done_callback(self._on_call_done)
+            self._bidi_rpc.open()
+
+            while self._bidi_rpc.is_active:
+                # Do not allow the paused status to change at all during this
+                # section. There is a condition where we could be resumed
+                # between checking if we are paused and calling wake.wait(),
+                # which means that we will miss the notification to wake up
+                # (oops!) and wait for a notification that will never come.
+                # Keeping the lock throughout avoids that.
+                # In the future, we could use `Condition.wait_for` if we drop
+                # Python 2.7.
+                # See: https://github.com/googleapis/python-api-core/issues/211
+                with self._wake:
+                    while self._paused:
+                        _LOGGER.debug("paused, waiting for waking.")
+                        self._wake.wait()
+                        _LOGGER.debug("woken.")
+
+                _LOGGER.debug("waiting for recv.")
+                response = self._bidi_rpc.recv()
+                _LOGGER.debug("recved response.")
+                self._on_response(response)
+
+        except exceptions.GoogleAPICallError as exc:
+            _LOGGER.debug(
+                "%s caught error %s and will exit. Generally this is due to "
+                "the RPC itself being cancelled and the error will be "
+                "surfaced to the calling code.",
+                _BIDIRECTIONAL_CONSUMER_NAME,
+                exc,
+                exc_info=True,
+            )
+
+        except Exception as exc:
+            _LOGGER.exception(
+                "%s caught unexpected exception %s and will exit.",
+                _BIDIRECTIONAL_CONSUMER_NAME,
+                exc,
+            )
+
+        _LOGGER.info("%s exiting", _BIDIRECTIONAL_CONSUMER_NAME)
+
+    def start(self):
+        """Start the background thread and begin consuming the thread."""
+        with self._operational_lock:
+            ready = threading.Event()
+            thread = threading.Thread(
+                name=_BIDIRECTIONAL_CONSUMER_NAME,
+                target=self._thread_main,
+                args=(ready,),
+            )
+            thread.daemon = True
+            thread.start()
+            # Other parts of the code rely on `thread.is_alive` which
+            # isn't sufficient to know if a thread is active, just that it may
+            # soon be active. This can cause races. Further protect
+            # against races by using a ready event and wait on it to be set.
+            ready.wait()
+            self._thread = thread
+            _LOGGER.debug("Started helper thread %s", thread.name)
+
+    def stop(self):
+        """Stop consuming the stream and shutdown the background thread."""
+        with self._operational_lock:
+            self._bidi_rpc.close()
+
+            if self._thread is not None:
+                # Resume the thread to wake it up in case it is sleeping.
+                self.resume()
+                # The daemonized thread may itself block, so don't wait
+                # for it longer than a second.
+                self._thread.join(1.0)
+                if self._thread.is_alive():  # pragma: NO COVER
+                    _LOGGER.warning("Background thread did not exit.")
+
+            self._thread = None
+
+    @property
+    def is_active(self):
+        """bool: True if the background thread is active."""
+        return self._thread is not None and self._thread.is_alive()
+
+    def pause(self):
+        """Pauses the response stream.
+
+        This does *not* pause the request stream.
+        """
+        with self._wake:
+            self._paused = True
+
+    def resume(self):
+        """Resumes the response stream."""
+        with self._wake:
+            self._paused = False
+            self._wake.notify_all()
+
+    @property
+    def is_paused(self):
+        """bool: True if the response stream is paused."""
+        return self._paused
diff --git a/google/api_core/client_info.py b/google/api_core/client_info.py
new file mode 100644
index 0000000..e093ffd
--- /dev/null
+++ b/google/api_core/client_info.py
@@ -0,0 +1,107 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helpers for providing client information.
+
+Client information is used to send information about the calling client,
+such as the library and Python version, to API services.
+"""
+
+import platform
+from typing import Union
+
+import pkg_resources
+
+from google.api_core import version as api_core_version
+
+_PY_VERSION = platform.python_version()
+_API_CORE_VERSION = api_core_version.__version__
+
+_GRPC_VERSION: Union[str, None]
+
+try:
+    _GRPC_VERSION = pkg_resources.get_distribution("grpcio").version
+except pkg_resources.DistributionNotFound:  # pragma: NO COVER
+    _GRPC_VERSION = None
+
+
+class ClientInfo(object):
+    """Client information used to generate a user-agent for API calls.
+
+    This user-agent information is sent along with API calls to allow the
+    receiving service to do analytics on which versions of Python and Google
+    libraries are being used.
+
+    Args:
+        python_version (str): The Python interpreter version, for example,
+            ``'3.9.6'``.
+        grpc_version (Optional[str]): The gRPC library version.
+        api_core_version (str): The google-api-core library version.
+        gapic_version (Optional[str]): The sversion of gapic-generated client
+            library, if the library was generated by gapic.
+        client_library_version (Optional[str]): The version of the client
+            library, generally used if the client library was not generated
+            by gapic or if additional functionality was built on top of
+            a gapic client library.
+        user_agent (Optional[str]): Prefix to the user agent header. This is
+            used to supply information such as application name or partner tool.
+            Recommended format: ``application-or-tool-ID/major.minor.version``.
+        rest_version (Optional[str]): The requests library version.
+    """
+
+    def __init__(
+        self,
+        python_version=_PY_VERSION,
+        grpc_version=_GRPC_VERSION,
+        api_core_version=_API_CORE_VERSION,
+        gapic_version=None,
+        client_library_version=None,
+        user_agent=None,
+        rest_version=None,
+    ):
+        self.python_version = python_version
+        self.grpc_version = grpc_version
+        self.api_core_version = api_core_version
+        self.gapic_version = gapic_version
+        self.client_library_version = client_library_version
+        self.user_agent = user_agent
+        self.rest_version = rest_version
+
+    def to_user_agent(self):
+        """Returns the user-agent string for this client info."""
+
+        # Note: the order here is important as the internal metrics system
+        # expects these items to be in specific locations.
+        ua = ""
+
+        if self.user_agent is not None:
+            ua += "{user_agent} "
+
+        ua += "gl-python/{python_version} "
+
+        if self.grpc_version is not None:
+            ua += "grpc/{grpc_version} "
+
+        if self.rest_version is not None:
+            ua += "rest/{rest_version} "
+
+        ua += "gax/{api_core_version} "
+
+        if self.gapic_version is not None:
+            ua += "gapic/{gapic_version} "
+
+        if self.client_library_version is not None:
+            ua += "gccl/{client_library_version} "
+
+        return ua.format(**self.__dict__).strip()
diff --git a/google/api_core/client_options.py b/google/api_core/client_options.py
new file mode 100644
index 0000000..be5523d
--- /dev/null
+++ b/google/api_core/client_options.py
@@ -0,0 +1,116 @@
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Client options class.
+
+Client options provide a consistent interface for user options to be defined
+across clients.
+
+You can pass a client options object to a client.
+
+.. code-block:: python
+
+    from google.api_core.client_options import ClientOptions
+    from google.cloud.vision_v1 import ImageAnnotatorClient
+
+    def get_client_cert():
+        # code to load client certificate and private key.
+        return client_cert_bytes, client_private_key_bytes
+
+    options = ClientOptions(api_endpoint="foo.googleapis.com",
+        client_cert_source=get_client_cert)
+
+    client = ImageAnnotatorClient(client_options=options)
+
+You can also pass a mapping object.
+
+.. code-block:: python
+
+    from google.cloud.vision_v1 import ImageAnnotatorClient
+
+    client = ImageAnnotatorClient(
+        client_options={
+            "api_endpoint": "foo.googleapis.com",
+            "client_cert_source" : get_client_cert
+        })
+
+
+"""
+
+
+class ClientOptions(object):
+    """Client Options used to set options on clients.
+
+    Args:
+        api_endpoint (Optional[str]): The desired API endpoint, e.g.,
+            compute.googleapis.com
+        client_cert_source (Optional[Callable[[], (bytes, bytes)]]): A callback
+            which returns client certificate bytes and private key bytes both in
+            PEM format. ``client_cert_source`` and ``client_encrypted_cert_source``
+            are mutually exclusive.
+        client_encrypted_cert_source (Optional[Callable[[], (str, str, bytes)]]):
+            A callback which returns client certificate file path, encrypted
+            private key file path, and the passphrase bytes.``client_cert_source``
+            and ``client_encrypted_cert_source`` are mutually exclusive.
+        quota_project_id (Optional[str]): A project name that a client's
+            quota belongs to.
+        credentials_file (Optional[str]): A path to a file storing credentials.
+        scopes (Optional[Sequence[str]]): OAuth access token override scopes.
+
+    Raises:
+        ValueError: If both ``client_cert_source`` and ``client_encrypted_cert_source``
+            are provided.
+    """
+
+    def __init__(
+        self,
+        api_endpoint=None,
+        client_cert_source=None,
+        client_encrypted_cert_source=None,
+        quota_project_id=None,
+        credentials_file=None,
+        scopes=None,
+    ):
+        if client_cert_source and client_encrypted_cert_source:
+            raise ValueError(
+                "client_cert_source and client_encrypted_cert_source are mutually exclusive"
+            )
+        self.api_endpoint = api_endpoint
+        self.client_cert_source = client_cert_source
+        self.client_encrypted_cert_source = client_encrypted_cert_source
+        self.quota_project_id = quota_project_id
+        self.credentials_file = credentials_file
+        self.scopes = scopes
+
+    def __repr__(self):
+        return "ClientOptions: " + repr(self.__dict__)
+
+
+def from_dict(options):
+    """Construct a client options object from a mapping object.
+
+    Args:
+        options (collections.abc.Mapping): A mapping object with client options.
+            See the docstring for ClientOptions for details on valid arguments.
+    """
+
+    client_options = ClientOptions()
+
+    for key, value in options.items():
+        if hasattr(client_options, key):
+            setattr(client_options, key, value)
+        else:
+            raise ValueError("ClientOptions does not accept an option '" + key + "'")
+
+    return client_options
diff --git a/google/api_core/datetime_helpers.py b/google/api_core/datetime_helpers.py
new file mode 100644
index 0000000..78268ef
--- /dev/null
+++ b/google/api_core/datetime_helpers.py
@@ -0,0 +1,298 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helpers for :mod:`datetime`."""
+
+import calendar
+import datetime
+import re
+
+from google.protobuf import timestamp_pb2
+
+
+_UTC_EPOCH = datetime.datetime(1970, 1, 1, tzinfo=datetime.timezone.utc)
+_RFC3339_MICROS = "%Y-%m-%dT%H:%M:%S.%fZ"
+_RFC3339_NO_FRACTION = "%Y-%m-%dT%H:%M:%S"
+# datetime.strptime cannot handle nanosecond precision:  parse w/ regex
+_RFC3339_NANOS = re.compile(
+    r"""
+    (?P<no_fraction>
+        \d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}  # YYYY-MM-DDTHH:MM:SS
+    )
+    (                                        # Optional decimal part
+     \.                                      # decimal point
+     (?P<nanos>\d{1,9})                      # nanoseconds, maybe truncated
+    )?
+    Z                                        # Zulu
+""",
+    re.VERBOSE,
+)
+
+
+def utcnow():
+    """A :meth:`datetime.datetime.utcnow()` alias to allow mocking in tests."""
+    return datetime.datetime.utcnow()
+
+
+def to_milliseconds(value):
+    """Convert a zone-aware datetime to milliseconds since the unix epoch.
+
+    Args:
+        value (datetime.datetime): The datetime to covert.
+
+    Returns:
+        int: Milliseconds since the unix epoch.
+    """
+    micros = to_microseconds(value)
+    return micros // 1000
+
+
+def from_microseconds(value):
+    """Convert timestamp in microseconds since the unix epoch to datetime.
+
+    Args:
+        value (float): The timestamp to convert, in microseconds.
+
+    Returns:
+        datetime.datetime: The datetime object equivalent to the timestamp in
+            UTC.
+    """
+    return _UTC_EPOCH + datetime.timedelta(microseconds=value)
+
+
+def to_microseconds(value):
+    """Convert a datetime to microseconds since the unix epoch.
+
+    Args:
+        value (datetime.datetime): The datetime to covert.
+
+    Returns:
+        int: Microseconds since the unix epoch.
+    """
+    if not value.tzinfo:
+        value = value.replace(tzinfo=datetime.timezone.utc)
+    # Regardless of what timezone is on the value, convert it to UTC.
+    value = value.astimezone(datetime.timezone.utc)
+    # Convert the datetime to a microsecond timestamp.
+    return int(calendar.timegm(value.timetuple()) * 1e6) + value.microsecond
+
+
+def from_iso8601_date(value):
+    """Convert a ISO8601 date string to a date.
+
+    Args:
+        value (str): The ISO8601 date string.
+
+    Returns:
+        datetime.date: A date equivalent to the date string.
+    """
+    return datetime.datetime.strptime(value, "%Y-%m-%d").date()
+
+
+def from_iso8601_time(value):
+    """Convert a zoneless ISO8601 time string to a time.
+
+    Args:
+        value (str): The ISO8601 time string.
+
+    Returns:
+        datetime.time: A time equivalent to the time string.
+    """
+    return datetime.datetime.strptime(value, "%H:%M:%S").time()
+
+
+def from_rfc3339(value):
+    """Convert an RFC3339-format timestamp to a native datetime.
+
+    Supported formats include those without fractional seconds, or with
+    any fraction up to nanosecond precision.
+
+    .. note::
+        Python datetimes do not support nanosecond precision; this function
+        therefore truncates such values to microseconds.
+
+    Args:
+        value (str): The RFC3339 string to convert.
+
+    Returns:
+        datetime.datetime: The datetime object equivalent to the timestamp
+        in UTC.
+
+    Raises:
+        ValueError: If the timestamp does not match the RFC3339
+            regular expression.
+    """
+    with_nanos = _RFC3339_NANOS.match(value)
+
+    if with_nanos is None:
+        raise ValueError(
+            "Timestamp: {!r}, does not match pattern: {!r}".format(
+                value, _RFC3339_NANOS.pattern
+            )
+        )
+
+    bare_seconds = datetime.datetime.strptime(
+        with_nanos.group("no_fraction"), _RFC3339_NO_FRACTION
+    )
+    fraction = with_nanos.group("nanos")
+
+    if fraction is None:
+        micros = 0
+    else:
+        scale = 9 - len(fraction)
+        nanos = int(fraction) * (10 ** scale)
+        micros = nanos // 1000
+
+    return bare_seconds.replace(microsecond=micros, tzinfo=datetime.timezone.utc)
+
+
+from_rfc3339_nanos = from_rfc3339  # from_rfc3339_nanos method was deprecated.
+
+
+def to_rfc3339(value, ignore_zone=True):
+    """Convert a datetime to an RFC3339 timestamp string.
+
+    Args:
+        value (datetime.datetime):
+            The datetime object to be converted to a string.
+        ignore_zone (bool): If True, then the timezone (if any) of the
+            datetime object is ignored and the datetime is treated as UTC.
+
+    Returns:
+        str: The RFC3339 formated string representing the datetime.
+    """
+    if not ignore_zone and value.tzinfo is not None:
+        # Convert to UTC and remove the time zone info.
+        value = value.replace(tzinfo=None) - value.utcoffset()
+
+    return value.strftime(_RFC3339_MICROS)
+
+
+class DatetimeWithNanoseconds(datetime.datetime):
+    """Track nanosecond in addition to normal datetime attrs.
+
+    Nanosecond can be passed only as a keyword argument.
+    """
+
+    __slots__ = ("_nanosecond",)
+
+    # pylint: disable=arguments-differ
+    def __new__(cls, *args, **kw):
+        nanos = kw.pop("nanosecond", 0)
+        if nanos > 0:
+            if "microsecond" in kw:
+                raise TypeError("Specify only one of 'microsecond' or 'nanosecond'")
+            kw["microsecond"] = nanos // 1000
+        inst = datetime.datetime.__new__(cls, *args, **kw)
+        inst._nanosecond = nanos or 0
+        return inst
+
+    # pylint: disable=arguments-differ
+
+    @property
+    def nanosecond(self):
+        """Read-only: nanosecond precision."""
+        return self._nanosecond
+
+    def rfc3339(self):
+        """Return an RFC3339-compliant timestamp.
+
+        Returns:
+            (str): Timestamp string according to RFC3339 spec.
+        """
+        if self._nanosecond == 0:
+            return to_rfc3339(self)
+        nanos = str(self._nanosecond).rjust(9, "0").rstrip("0")
+        return "{}.{}Z".format(self.strftime(_RFC3339_NO_FRACTION), nanos)
+
+    @classmethod
+    def from_rfc3339(cls, stamp):
+        """Parse RFC3339-compliant timestamp, preserving nanoseconds.
+
+        Args:
+            stamp (str): RFC3339 stamp, with up to nanosecond precision
+
+        Returns:
+            :class:`DatetimeWithNanoseconds`:
+                an instance matching the timestamp string
+
+        Raises:
+            ValueError: if `stamp` does not match the expected format
+        """
+        with_nanos = _RFC3339_NANOS.match(stamp)
+        if with_nanos is None:
+            raise ValueError(
+                "Timestamp: {}, does not match pattern: {}".format(
+                    stamp, _RFC3339_NANOS.pattern
+                )
+            )
+        bare = datetime.datetime.strptime(
+            with_nanos.group("no_fraction"), _RFC3339_NO_FRACTION
+        )
+        fraction = with_nanos.group("nanos")
+        if fraction is None:
+            nanos = 0
+        else:
+            scale = 9 - len(fraction)
+            nanos = int(fraction) * (10 ** scale)
+        return cls(
+            bare.year,
+            bare.month,
+            bare.day,
+            bare.hour,
+            bare.minute,
+            bare.second,
+            nanosecond=nanos,
+            tzinfo=datetime.timezone.utc,
+        )
+
+    def timestamp_pb(self):
+        """Return a timestamp message.
+
+        Returns:
+            (:class:`~google.protobuf.timestamp_pb2.Timestamp`): Timestamp message
+        """
+        inst = (
+            self
+            if self.tzinfo is not None
+            else self.replace(tzinfo=datetime.timezone.utc)
+        )
+        delta = inst - _UTC_EPOCH
+        seconds = int(delta.total_seconds())
+        nanos = self._nanosecond or self.microsecond * 1000
+        return timestamp_pb2.Timestamp(seconds=seconds, nanos=nanos)
+
+    @classmethod
+    def from_timestamp_pb(cls, stamp):
+        """Parse RFC3339-compliant timestamp, preserving nanoseconds.
+
+        Args:
+            stamp (:class:`~google.protobuf.timestamp_pb2.Timestamp`): timestamp message
+
+        Returns:
+            :class:`DatetimeWithNanoseconds`:
+                an instance matching the timestamp message
+        """
+        microseconds = int(stamp.seconds * 1e6)
+        bare = from_microseconds(microseconds)
+        return cls(
+            bare.year,
+            bare.month,
+            bare.day,
+            bare.hour,
+            bare.minute,
+            bare.second,
+            nanosecond=stamp.nanos,
+            tzinfo=datetime.timezone.utc,
+        )
diff --git a/google/api_core/exceptions.py b/google/api_core/exceptions.py
new file mode 100644
index 0000000..6b1b6f7
--- /dev/null
+++ b/google/api_core/exceptions.py
@@ -0,0 +1,546 @@
+# Copyright 2014 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Exceptions raised by Google API core & clients.
+
+This module provides base classes for all errors raised by libraries based
+on :mod:`google.api_core`, including both HTTP and gRPC clients.
+"""
+
+from __future__ import absolute_import
+from __future__ import unicode_literals
+
+import http.client
+from typing import Dict
+from typing import Union
+
+from google.rpc import error_details_pb2
+
+try:
+    import grpc
+    from grpc_status import rpc_status
+except ImportError:  # pragma: NO COVER
+    grpc = None
+    rpc_status = None
+
+# Lookup tables for mapping exceptions from HTTP and gRPC transports.
+# Populated by _GoogleAPICallErrorMeta
+_HTTP_CODE_TO_EXCEPTION: Dict[int, Exception] = {}
+_GRPC_CODE_TO_EXCEPTION: Dict[int, Exception] = {}
+
+# Additional lookup table to map integer status codes to grpc status code
+# grpc does not currently support initializing enums from ints
+# i.e., grpc.StatusCode(5) raises an error
+_INT_TO_GRPC_CODE = {}
+if grpc is not None:  # pragma: no branch
+    for x in grpc.StatusCode:
+        _INT_TO_GRPC_CODE[x.value[0]] = x
+
+
+class GoogleAPIError(Exception):
+    """Base class for all exceptions raised by Google API Clients."""
+
+    pass
+
+
+class DuplicateCredentialArgs(GoogleAPIError):
+    """Raised when multiple credentials are passed."""
+
+    pass
+
+
+class RetryError(GoogleAPIError):
+    """Raised when a function has exhausted all of its available retries.
+
+    Args:
+        message (str): The exception message.
+        cause (Exception): The last exception raised when retring the
+            function.
+    """
+
+    def __init__(self, message, cause):
+        super(RetryError, self).__init__(message)
+        self.message = message
+        self._cause = cause
+
+    @property
+    def cause(self):
+        """The last exception raised when retrying the function."""
+        return self._cause
+
+    def __str__(self):
+        return "{}, last exception: {}".format(self.message, self.cause)
+
+
+class _GoogleAPICallErrorMeta(type):
+    """Metaclass for registering GoogleAPICallError subclasses."""
+
+    def __new__(mcs, name, bases, class_dict):
+        cls = type.__new__(mcs, name, bases, class_dict)
+        if cls.code is not None:
+            _HTTP_CODE_TO_EXCEPTION.setdefault(cls.code, cls)
+        if cls.grpc_status_code is not None:
+            _GRPC_CODE_TO_EXCEPTION.setdefault(cls.grpc_status_code, cls)
+        return cls
+
+
+class GoogleAPICallError(GoogleAPIError, metaclass=_GoogleAPICallErrorMeta):
+    """Base class for exceptions raised by calling API methods.
+
+    Args:
+        message (str): The exception message.
+        errors (Sequence[Any]): An optional list of error details.
+        details (Sequence[Any]): An optional list of objects defined in google.rpc.error_details.
+        response (Union[requests.Request, grpc.Call]): The response or
+            gRPC call metadata.
+    """
+
+    code: Union[int, None] = None
+    """Optional[int]: The HTTP status code associated with this error.
+
+    This may be ``None`` if the exception does not have a direct mapping
+    to an HTTP error.
+
+    See http://www.w3.org/Protocols/rfc2616/rfc2616-sec10.html
+    """
+
+    grpc_status_code = None
+    """Optional[grpc.StatusCode]: The gRPC status code associated with this
+    error.
+
+    This may be ``None`` if the exception does not match up to a gRPC error.
+    """
+
+    def __init__(self, message, errors=(), details=(), response=None):
+        super(GoogleAPICallError, self).__init__(message)
+        self.message = message
+        """str: The exception message."""
+        self._errors = errors
+        self._details = details
+        self._response = response
+
+    def __str__(self):
+        if self.details:
+            return "{} {} {}".format(self.code, self.message, self.details)
+        else:
+            return "{} {}".format(self.code, self.message)
+
+    @property
+    def errors(self):
+        """Detailed error information.
+
+        Returns:
+            Sequence[Any]: A list of additional error details.
+        """
+        return list(self._errors)
+
+    @property
+    def details(self):
+        """Information contained in google.rpc.status.details.
+
+        Reference:
+            https://github.com/googleapis/googleapis/blob/master/google/rpc/status.proto
+            https://github.com/googleapis/googleapis/blob/master/google/rpc/error_details.proto
+
+        Returns:
+            Sequence[Any]: A list of structured objects from error_details.proto
+       """
+        return list(self._details)
+
+    @property
+    def response(self):
+        """Optional[Union[requests.Request, grpc.Call]]: The response or
+        gRPC call metadata."""
+        return self._response
+
+
+class Redirection(GoogleAPICallError):
+    """Base class for for all redirection (HTTP 3xx) responses."""
+
+
+class MovedPermanently(Redirection):
+    """Exception mapping a ``301 Moved Permanently`` response."""
+
+    code = http.client.MOVED_PERMANENTLY
+
+
+class NotModified(Redirection):
+    """Exception mapping a ``304 Not Modified`` response."""
+
+    code = http.client.NOT_MODIFIED
+
+
+class TemporaryRedirect(Redirection):
+    """Exception mapping a ``307 Temporary Redirect`` response."""
+
+    code = http.client.TEMPORARY_REDIRECT
+
+
+class ResumeIncomplete(Redirection):
+    """Exception mapping a ``308 Resume Incomplete`` response.
+
+    .. note:: :attr:`http.client.PERMANENT_REDIRECT` is ``308``, but Google
+        APIs differ in their use of this status code.
+    """
+
+    code = 308
+
+
+class ClientError(GoogleAPICallError):
+    """Base class for all client error (HTTP 4xx) responses."""
+
+
+class BadRequest(ClientError):
+    """Exception mapping a ``400 Bad Request`` response."""
+
+    code = http.client.BAD_REQUEST
+
+
+class InvalidArgument(BadRequest):
+    """Exception mapping a :attr:`grpc.StatusCode.INVALID_ARGUMENT` error."""
+
+    grpc_status_code = grpc.StatusCode.INVALID_ARGUMENT if grpc is not None else None
+
+
+class FailedPrecondition(BadRequest):
+    """Exception mapping a :attr:`grpc.StatusCode.FAILED_PRECONDITION`
+    error."""
+
+    grpc_status_code = grpc.StatusCode.FAILED_PRECONDITION if grpc is not None else None
+
+
+class OutOfRange(BadRequest):
+    """Exception mapping a :attr:`grpc.StatusCode.OUT_OF_RANGE` error."""
+
+    grpc_status_code = grpc.StatusCode.OUT_OF_RANGE if grpc is not None else None
+
+
+class Unauthorized(ClientError):
+    """Exception mapping a ``401 Unauthorized`` response."""
+
+    code = http.client.UNAUTHORIZED
+
+
+class Unauthenticated(Unauthorized):
+    """Exception mapping a :attr:`grpc.StatusCode.UNAUTHENTICATED` error."""
+
+    grpc_status_code = grpc.StatusCode.UNAUTHENTICATED if grpc is not None else None
+
+
+class Forbidden(ClientError):
+    """Exception mapping a ``403 Forbidden`` response."""
+
+    code = http.client.FORBIDDEN
+
+
+class PermissionDenied(Forbidden):
+    """Exception mapping a :attr:`grpc.StatusCode.PERMISSION_DENIED` error."""
+
+    grpc_status_code = grpc.StatusCode.PERMISSION_DENIED if grpc is not None else None
+
+
+class NotFound(ClientError):
+    """Exception mapping a ``404 Not Found`` response or a
+    :attr:`grpc.StatusCode.NOT_FOUND` error."""
+
+    code = http.client.NOT_FOUND
+    grpc_status_code = grpc.StatusCode.NOT_FOUND if grpc is not None else None
+
+
+class MethodNotAllowed(ClientError):
+    """Exception mapping a ``405 Method Not Allowed`` response."""
+
+    code = http.client.METHOD_NOT_ALLOWED
+
+
+class Conflict(ClientError):
+    """Exception mapping a ``409 Conflict`` response."""
+
+    code = http.client.CONFLICT
+
+
+class AlreadyExists(Conflict):
+    """Exception mapping a :attr:`grpc.StatusCode.ALREADY_EXISTS` error."""
+
+    grpc_status_code = grpc.StatusCode.ALREADY_EXISTS if grpc is not None else None
+
+
+class Aborted(Conflict):
+    """Exception mapping a :attr:`grpc.StatusCode.ABORTED` error."""
+
+    grpc_status_code = grpc.StatusCode.ABORTED if grpc is not None else None
+
+
+class LengthRequired(ClientError):
+    """Exception mapping a ``411 Length Required`` response."""
+
+    code = http.client.LENGTH_REQUIRED
+
+
+class PreconditionFailed(ClientError):
+    """Exception mapping a ``412 Precondition Failed`` response."""
+
+    code = http.client.PRECONDITION_FAILED
+
+
+class RequestRangeNotSatisfiable(ClientError):
+    """Exception mapping a ``416 Request Range Not Satisfiable`` response."""
+
+    code = http.client.REQUESTED_RANGE_NOT_SATISFIABLE
+
+
+class TooManyRequests(ClientError):
+    """Exception mapping a ``429 Too Many Requests`` response."""
+
+    code = http.client.TOO_MANY_REQUESTS
+
+
+class ResourceExhausted(TooManyRequests):
+    """Exception mapping a :attr:`grpc.StatusCode.RESOURCE_EXHAUSTED` error."""
+
+    grpc_status_code = grpc.StatusCode.RESOURCE_EXHAUSTED if grpc is not None else None
+
+
+class Cancelled(ClientError):
+    """Exception mapping a :attr:`grpc.StatusCode.CANCELLED` error."""
+
+    # This maps to HTTP status code 499. See
+    # https://github.com/googleapis/googleapis/blob/master/google/rpc/code.proto
+    code = 499
+    grpc_status_code = grpc.StatusCode.CANCELLED if grpc is not None else None
+
+
+class ServerError(GoogleAPICallError):
+    """Base for 5xx responses."""
+
+
+class InternalServerError(ServerError):
+    """Exception mapping a ``500 Internal Server Error`` response. or a
+    :attr:`grpc.StatusCode.INTERNAL` error."""
+
+    code = http.client.INTERNAL_SERVER_ERROR
+    grpc_status_code = grpc.StatusCode.INTERNAL if grpc is not None else None
+
+
+class Unknown(ServerError):
+    """Exception mapping a :attr:`grpc.StatusCode.UNKNOWN` error."""
+
+    grpc_status_code = grpc.StatusCode.UNKNOWN if grpc is not None else None
+
+
+class DataLoss(ServerError):
+    """Exception mapping a :attr:`grpc.StatusCode.DATA_LOSS` error."""
+
+    grpc_status_code = grpc.StatusCode.DATA_LOSS if grpc is not None else None
+
+
+class MethodNotImplemented(ServerError):
+    """Exception mapping a ``501 Not Implemented`` response or a
+    :attr:`grpc.StatusCode.UNIMPLEMENTED` error."""
+
+    code = http.client.NOT_IMPLEMENTED
+    grpc_status_code = grpc.StatusCode.UNIMPLEMENTED if grpc is not None else None
+
+
+class BadGateway(ServerError):
+    """Exception mapping a ``502 Bad Gateway`` response."""
+
+    code = http.client.BAD_GATEWAY
+
+
+class ServiceUnavailable(ServerError):
+    """Exception mapping a ``503 Service Unavailable`` response or a
+    :attr:`grpc.StatusCode.UNAVAILABLE` error."""
+
+    code = http.client.SERVICE_UNAVAILABLE
+    grpc_status_code = grpc.StatusCode.UNAVAILABLE if grpc is not None else None
+
+
+class GatewayTimeout(ServerError):
+    """Exception mapping a ``504 Gateway Timeout`` response."""
+
+    code = http.client.GATEWAY_TIMEOUT
+
+
+class DeadlineExceeded(GatewayTimeout):
+    """Exception mapping a :attr:`grpc.StatusCode.DEADLINE_EXCEEDED` error."""
+
+    grpc_status_code = grpc.StatusCode.DEADLINE_EXCEEDED if grpc is not None else None
+
+
+def exception_class_for_http_status(status_code):
+    """Return the exception class for a specific HTTP status code.
+
+    Args:
+        status_code (int): The HTTP status code.
+
+    Returns:
+        :func:`type`: the appropriate subclass of :class:`GoogleAPICallError`.
+    """
+    return _HTTP_CODE_TO_EXCEPTION.get(status_code, GoogleAPICallError)
+
+
+def from_http_status(status_code, message, **kwargs):
+    """Create a :class:`GoogleAPICallError` from an HTTP status code.
+
+    Args:
+        status_code (int): The HTTP status code.
+        message (str): The exception message.
+        kwargs: Additional arguments passed to the :class:`GoogleAPICallError`
+            constructor.
+
+    Returns:
+        GoogleAPICallError: An instance of the appropriate subclass of
+            :class:`GoogleAPICallError`.
+    """
+    error_class = exception_class_for_http_status(status_code)
+    error = error_class(message, **kwargs)
+
+    if error.code is None:
+        error.code = status_code
+
+    return error
+
+
+def from_http_response(response):
+    """Create a :class:`GoogleAPICallError` from a :class:`requests.Response`.
+
+    Args:
+        response (requests.Response): The HTTP response.
+
+    Returns:
+        GoogleAPICallError: An instance of the appropriate subclass of
+            :class:`GoogleAPICallError`, with the message and errors populated
+            from the response.
+    """
+    try:
+        payload = response.json()
+    except ValueError:
+        payload = {"error": {"message": response.text or "unknown error"}}
+
+    error_message = payload.get("error", {}).get("message", "unknown error")
+    errors = payload.get("error", {}).get("errors", ())
+    # In JSON, details are already formatted in developer-friendly way.
+    details = payload.get("error", {}).get("details", ())
+
+    message = "{method} {url}: {error}".format(
+        method=response.request.method, url=response.request.url, error=error_message
+    )
+
+    exception = from_http_status(
+        response.status_code, message, errors=errors, details=details, response=response
+    )
+    return exception
+
+
+def exception_class_for_grpc_status(status_code):
+    """Return the exception class for a specific :class:`grpc.StatusCode`.
+
+    Args:
+        status_code (grpc.StatusCode): The gRPC status code.
+
+    Returns:
+        :func:`type`: the appropriate subclass of :class:`GoogleAPICallError`.
+    """
+    return _GRPC_CODE_TO_EXCEPTION.get(status_code, GoogleAPICallError)
+
+
+def from_grpc_status(status_code, message, **kwargs):
+    """Create a :class:`GoogleAPICallError` from a :class:`grpc.StatusCode`.
+
+    Args:
+        status_code (Union[grpc.StatusCode, int]): The gRPC status code.
+        message (str): The exception message.
+        kwargs: Additional arguments passed to the :class:`GoogleAPICallError`
+            constructor.
+
+    Returns:
+        GoogleAPICallError: An instance of the appropriate subclass of
+            :class:`GoogleAPICallError`.
+    """
+
+    if isinstance(status_code, int):
+        status_code = _INT_TO_GRPC_CODE.get(status_code, status_code)
+
+    error_class = exception_class_for_grpc_status(status_code)
+    error = error_class(message, **kwargs)
+
+    if error.grpc_status_code is None:
+        error.grpc_status_code = status_code
+
+    return error
+
+
+def _is_informative_grpc_error(rpc_exc):
+    return hasattr(rpc_exc, "code") and hasattr(rpc_exc, "details")
+
+
+def _parse_grpc_error_details(rpc_exc):
+    try:
+        status = rpc_status.from_call(rpc_exc)
+    except NotImplementedError:  # workaround
+        return []
+
+    if not status:
+        return []
+
+    possible_errors = [
+        error_details_pb2.BadRequest,
+        error_details_pb2.PreconditionFailure,
+        error_details_pb2.QuotaFailure,
+        error_details_pb2.ErrorInfo,
+        error_details_pb2.RetryInfo,
+        error_details_pb2.ResourceInfo,
+        error_details_pb2.RequestInfo,
+        error_details_pb2.DebugInfo,
+        error_details_pb2.Help,
+        error_details_pb2.LocalizedMessage,
+    ]
+    error_details = []
+    for detail in status.details:
+        matched_detail_cls = list(
+            filter(lambda x: detail.Is(x.DESCRIPTOR), possible_errors)
+        )
+        # If nothing matched, use detail directly.
+        if len(matched_detail_cls) == 0:
+            info = detail
+        else:
+            info = matched_detail_cls[0]()
+            detail.Unpack(info)
+        error_details.append(info)
+    return error_details
+
+
+def from_grpc_error(rpc_exc):
+    """Create a :class:`GoogleAPICallError` from a :class:`grpc.RpcError`.
+
+    Args:
+        rpc_exc (grpc.RpcError): The gRPC error.
+
+    Returns:
+        GoogleAPICallError: An instance of the appropriate subclass of
+            :class:`GoogleAPICallError`.
+    """
+    # NOTE(lidiz) All gRPC error shares the parent class grpc.RpcError.
+    # However, check for grpc.RpcError breaks backward compatibility.
+    if isinstance(rpc_exc, grpc.Call) or _is_informative_grpc_error(rpc_exc):
+        return from_grpc_status(
+            rpc_exc.code(),
+            rpc_exc.details(),
+            errors=(rpc_exc,),
+            details=_parse_grpc_error_details(rpc_exc),
+            response=rpc_exc,
+        )
+    else:
+        return GoogleAPICallError(str(rpc_exc), errors=(rpc_exc,), response=rpc_exc)
diff --git a/google/api_core/future/__init__.py b/google/api_core/future/__init__.py
new file mode 100644
index 0000000..3768b2c
--- /dev/null
+++ b/google/api_core/future/__init__.py
@@ -0,0 +1,19 @@
+# Copyright 2017, Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Futures for dealing with asynchronous operations."""
+
+from google.api_core.future.base import Future
+
+__all__ = ["Future"]
diff --git a/google/api_core/future/_helpers.py b/google/api_core/future/_helpers.py
new file mode 100644
index 0000000..9e88ca9
--- /dev/null
+++ b/google/api_core/future/_helpers.py
@@ -0,0 +1,39 @@
+# Copyright 2017, Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Private helpers for futures."""
+
+import logging
+import threading
+
+
+_LOGGER = logging.getLogger(__name__)
+
+
+def start_daemon_thread(*args, **kwargs):
+    """Starts a thread and marks it as a daemon thread."""
+    thread = threading.Thread(*args, **kwargs)
+    thread.daemon = True
+    thread.start()
+    return thread
+
+
+def safe_invoke_callback(callback, *args, **kwargs):
+    """Invoke a callback, swallowing and logging any exceptions."""
+    # pylint: disable=bare-except
+    # We intentionally want to swallow all exceptions.
+    try:
+        return callback(*args, **kwargs)
+    except Exception:
+        _LOGGER.exception("Error while executing Future callback.")
diff --git a/google/api_core/future/async_future.py b/google/api_core/future/async_future.py
new file mode 100644
index 0000000..88c183f
--- /dev/null
+++ b/google/api_core/future/async_future.py
@@ -0,0 +1,162 @@
+# Copyright 2020, Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""AsyncIO implementation of the abstract base Future class."""
+
+import asyncio
+
+from google.api_core import exceptions
+from google.api_core import retry
+from google.api_core import retry_async
+from google.api_core.future import base
+
+
+class _OperationNotComplete(Exception):
+    """Private exception used for polling via retry."""
+
+    pass
+
+
+RETRY_PREDICATE = retry.if_exception_type(
+    _OperationNotComplete,
+    exceptions.TooManyRequests,
+    exceptions.InternalServerError,
+    exceptions.BadGateway,
+)
+DEFAULT_RETRY = retry_async.AsyncRetry(predicate=RETRY_PREDICATE)
+
+
+class AsyncFuture(base.Future):
+    """A Future that polls peer service to self-update.
+
+    The :meth:`done` method should be implemented by subclasses. The polling
+    behavior will repeatedly call ``done`` until it returns True.
+
+    .. note::
+
+        Privacy here is intended to prevent the final class from
+        overexposing, not to prevent subclasses from accessing methods.
+
+    Args:
+        retry (google.api_core.retry.Retry): The retry configuration used
+            when polling. This can be used to control how often :meth:`done`
+            is polled. Regardless of the retry's ``deadline``, it will be
+            overridden by the ``timeout`` argument to :meth:`result`.
+    """
+
+    def __init__(self, retry=DEFAULT_RETRY):
+        super().__init__()
+        self._retry = retry
+        self._future = asyncio.get_event_loop().create_future()
+        self._background_task = None
+
+    async def done(self, retry=DEFAULT_RETRY):
+        """Checks to see if the operation is complete.
+
+        Args:
+            retry (google.api_core.retry.Retry): (Optional) How to retry the RPC.
+
+        Returns:
+            bool: True if the operation is complete, False otherwise.
+        """
+        # pylint: disable=redundant-returns-doc, missing-raises-doc
+        raise NotImplementedError()
+
+    async def _done_or_raise(self):
+        """Check if the future is done and raise if it's not."""
+        result = await self.done()
+        if not result:
+            raise _OperationNotComplete()
+
+    async def running(self):
+        """True if the operation is currently running."""
+        result = await self.done()
+        return not result
+
+    async def _blocking_poll(self, timeout=None):
+        """Poll and await for the Future to be resolved.
+
+        Args:
+            timeout (int):
+                How long (in seconds) to wait for the operation to complete.
+                If None, wait indefinitely.
+        """
+        if self._future.done():
+            return
+
+        retry_ = self._retry.with_deadline(timeout)
+
+        try:
+            await retry_(self._done_or_raise)()
+        except exceptions.RetryError:
+            raise asyncio.TimeoutError(
+                "Operation did not complete within the designated " "timeout."
+            )
+
+    async def result(self, timeout=None):
+        """Get the result of the operation.
+
+        Args:
+            timeout (int):
+                How long (in seconds) to wait for the operation to complete.
+                If None, wait indefinitely.
+
+        Returns:
+            google.protobuf.Message: The Operation's result.
+
+        Raises:
+            google.api_core.GoogleAPICallError: If the operation errors or if
+                the timeout is reached before the operation completes.
+        """
+        await self._blocking_poll(timeout=timeout)
+        return self._future.result()
+
+    async def exception(self, timeout=None):
+        """Get the exception from the operation.
+
+        Args:
+            timeout (int): How long to wait for the operation to complete.
+                If None, wait indefinitely.
+
+        Returns:
+            Optional[google.api_core.GoogleAPICallError]: The operation's
+                error.
+        """
+        await self._blocking_poll(timeout=timeout)
+        return self._future.exception()
+
+    def add_done_callback(self, fn):
+        """Add a callback to be executed when the operation is complete.
+
+        If the operation is completed, the callback will be scheduled onto the
+        event loop. Otherwise, the callback will be stored and invoked when the
+        future is done.
+
+        Args:
+            fn (Callable[Future]): The callback to execute when the operation
+                is complete.
+        """
+        if self._background_task is None:
+            self._background_task = asyncio.get_event_loop().create_task(
+                self._blocking_poll()
+            )
+        self._future.add_done_callback(fn)
+
+    def set_result(self, result):
+        """Set the Future's result."""
+        self._future.set_result(result)
+
+    def set_exception(self, exception):
+        """Set the Future's exception."""
+        self._future.set_exception(exception)
diff --git a/google/api_core/future/base.py b/google/api_core/future/base.py
new file mode 100644
index 0000000..f300586
--- /dev/null
+++ b/google/api_core/future/base.py
@@ -0,0 +1,64 @@
+# Copyright 2017, Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Abstract and helper bases for Future implementations."""
+
+import abc
+
+
+class Future(object, metaclass=abc.ABCMeta):
+    # pylint: disable=missing-docstring
+    # We inherit the interfaces here from concurrent.futures.
+
+    """Future interface.
+
+    This interface is based on :class:`concurrent.futures.Future`.
+    """
+
+    @abc.abstractmethod
+    def cancel(self):
+        raise NotImplementedError()
+
+    @abc.abstractmethod
+    def cancelled(self):
+        raise NotImplementedError()
+
+    @abc.abstractmethod
+    def running(self):
+        raise NotImplementedError()
+
+    @abc.abstractmethod
+    def done(self):
+        raise NotImplementedError()
+
+    @abc.abstractmethod
+    def result(self, timeout=None):
+        raise NotImplementedError()
+
+    @abc.abstractmethod
+    def exception(self, timeout=None):
+        raise NotImplementedError()
+
+    @abc.abstractmethod
+    def add_done_callback(self, fn):
+        # pylint: disable=invalid-name
+        raise NotImplementedError()
+
+    @abc.abstractmethod
+    def set_result(self, result):
+        raise NotImplementedError()
+
+    @abc.abstractmethod
+    def set_exception(self, exception):
+        raise NotImplementedError()
diff --git a/google/api_core/future/polling.py b/google/api_core/future/polling.py
new file mode 100644
index 0000000..02e680f
--- /dev/null
+++ b/google/api_core/future/polling.py
@@ -0,0 +1,193 @@
+# Copyright 2017, Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Abstract and helper bases for Future implementations."""
+
+import abc
+import concurrent.futures
+
+from google.api_core import exceptions
+from google.api_core import retry
+from google.api_core.future import _helpers
+from google.api_core.future import base
+
+
+class _OperationNotComplete(Exception):
+    """Private exception used for polling via retry."""
+
+    pass
+
+
+RETRY_PREDICATE = retry.if_exception_type(
+    _OperationNotComplete,
+    exceptions.TooManyRequests,
+    exceptions.InternalServerError,
+    exceptions.BadGateway,
+    exceptions.ServiceUnavailable,
+)
+DEFAULT_RETRY = retry.Retry(predicate=RETRY_PREDICATE)
+
+
+class PollingFuture(base.Future):
+    """A Future that needs to poll some service to check its status.
+
+    The :meth:`done` method should be implemented by subclasses. The polling
+    behavior will repeatedly call ``done`` until it returns True.
+
+    .. note::
+
+        Privacy here is intended to prevent the final class from
+        overexposing, not to prevent subclasses from accessing methods.
+
+    Args:
+        retry (google.api_core.retry.Retry): The retry configuration used
+            when polling. This can be used to control how often :meth:`done`
+            is polled. Regardless of the retry's ``deadline``, it will be
+            overridden by the ``timeout`` argument to :meth:`result`.
+    """
+
+    def __init__(self, retry=DEFAULT_RETRY):
+        super(PollingFuture, self).__init__()
+        self._retry = retry
+        self._result = None
+        self._exception = None
+        self._result_set = False
+        """bool: Set to True when the result has been set via set_result or
+        set_exception."""
+        self._polling_thread = None
+        self._done_callbacks = []
+
+    @abc.abstractmethod
+    def done(self, retry=DEFAULT_RETRY):
+        """Checks to see if the operation is complete.
+
+        Args:
+            retry (google.api_core.retry.Retry): (Optional) How to retry the RPC.
+
+        Returns:
+            bool: True if the operation is complete, False otherwise.
+        """
+        # pylint: disable=redundant-returns-doc, missing-raises-doc
+        raise NotImplementedError()
+
+    def _done_or_raise(self, retry=DEFAULT_RETRY):
+        """Check if the future is done and raise if it's not."""
+        kwargs = {} if retry is DEFAULT_RETRY else {"retry": retry}
+
+        if not self.done(**kwargs):
+            raise _OperationNotComplete()
+
+    def running(self):
+        """True if the operation is currently running."""
+        return not self.done()
+
+    def _blocking_poll(self, timeout=None, retry=DEFAULT_RETRY):
+        """Poll and wait for the Future to be resolved.
+
+        Args:
+            timeout (int):
+                How long (in seconds) to wait for the operation to complete.
+                If None, wait indefinitely.
+        """
+        if self._result_set:
+            return
+
+        retry_ = self._retry.with_deadline(timeout)
+
+        try:
+            kwargs = {} if retry is DEFAULT_RETRY else {"retry": retry}
+            retry_(self._done_or_raise)(**kwargs)
+        except exceptions.RetryError:
+            raise concurrent.futures.TimeoutError(
+                "Operation did not complete within the designated " "timeout."
+            )
+
+    def result(self, timeout=None, retry=DEFAULT_RETRY):
+        """Get the result of the operation, blocking if necessary.
+
+        Args:
+            timeout (int):
+                How long (in seconds) to wait for the operation to complete.
+                If None, wait indefinitely.
+
+        Returns:
+            google.protobuf.Message: The Operation's result.
+
+        Raises:
+            google.api_core.GoogleAPICallError: If the operation errors or if
+                the timeout is reached before the operation completes.
+        """
+        kwargs = {} if retry is DEFAULT_RETRY else {"retry": retry}
+        self._blocking_poll(timeout=timeout, **kwargs)
+
+        if self._exception is not None:
+            # pylint: disable=raising-bad-type
+            # Pylint doesn't recognize that this is valid in this case.
+            raise self._exception
+
+        return self._result
+
+    def exception(self, timeout=None):
+        """Get the exception from the operation, blocking if necessary.
+
+        Args:
+            timeout (int): How long to wait for the operation to complete.
+                If None, wait indefinitely.
+
+        Returns:
+            Optional[google.api_core.GoogleAPICallError]: The operation's
+                error.
+        """
+        self._blocking_poll(timeout=timeout)
+        return self._exception
+
+    def add_done_callback(self, fn):
+        """Add a callback to be executed when the operation is complete.
+
+        If the operation is not already complete, this will start a helper
+        thread to poll for the status of the operation in the background.
+
+        Args:
+            fn (Callable[Future]): The callback to execute when the operation
+                is complete.
+        """
+        if self._result_set:
+            _helpers.safe_invoke_callback(fn, self)
+            return
+
+        self._done_callbacks.append(fn)
+
+        if self._polling_thread is None:
+            # The polling thread will exit on its own as soon as the operation
+            # is done.
+            self._polling_thread = _helpers.start_daemon_thread(
+                target=self._blocking_poll
+            )
+
+    def _invoke_callbacks(self, *args, **kwargs):
+        """Invoke all done callbacks."""
+        for callback in self._done_callbacks:
+            _helpers.safe_invoke_callback(callback, *args, **kwargs)
+
+    def set_result(self, result):
+        """Set the Future's result."""
+        self._result = result
+        self._result_set = True
+        self._invoke_callbacks(self)
+
+    def set_exception(self, exception):
+        """Set the Future's exception."""
+        self._exception = exception
+        self._result_set = True
+        self._invoke_callbacks(self)
diff --git a/google/api_core/gapic_v1/__init__.py b/google/api_core/gapic_v1/__init__.py
new file mode 100644
index 0000000..e5b7ad3
--- /dev/null
+++ b/google/api_core/gapic_v1/__init__.py
@@ -0,0 +1,29 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from google.api_core.gapic_v1 import client_info
+from google.api_core.gapic_v1 import config
+from google.api_core.gapic_v1 import config_async
+from google.api_core.gapic_v1 import method
+from google.api_core.gapic_v1 import method_async
+from google.api_core.gapic_v1 import routing_header
+
+__all__ = [
+    "client_info",
+    "config",
+    "config_async",
+    "method",
+    "method_async",
+    "routing_header",
+]
diff --git a/google/api_core/gapic_v1/client_info.py b/google/api_core/gapic_v1/client_info.py
new file mode 100644
index 0000000..fab0f54
--- /dev/null
+++ b/google/api_core/gapic_v1/client_info.py
@@ -0,0 +1,55 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helpers for providing client information.
+
+Client information is used to send information about the calling client,
+such as the library and Python version, to API services.
+"""
+
+from google.api_core import client_info
+
+
+METRICS_METADATA_KEY = "x-goog-api-client"
+
+
+class ClientInfo(client_info.ClientInfo):
+    """Client information used to generate a user-agent for API calls.
+
+    This user-agent information is sent along with API calls to allow the
+    receiving service to do analytics on which versions of Python and Google
+    libraries are being used.
+
+    Args:
+        python_version (str): The Python interpreter version, for example,
+            ``'3.9.6'``.
+        grpc_version (Optional[str]): The gRPC library version.
+        api_core_version (str): The google-api-core library version.
+        gapic_version (Optional[str]): The sversion of gapic-generated client
+            library, if the library was generated by gapic.
+        client_library_version (Optional[str]): The version of the client
+            library, generally used if the client library was not generated
+            by gapic or if additional functionality was built on top of
+            a gapic client library.
+        user_agent (Optional[str]): Prefix to the user agent header. This is
+            used to supply information such as application name or partner tool.
+            Recommended format: ``application-or-tool-ID/major.minor.version``.
+    """
+
+    def to_grpc_metadata(self):
+        """Returns the gRPC metadata for this client info."""
+        return (METRICS_METADATA_KEY, self.to_user_agent())
+
+
+DEFAULT_CLIENT_INFO = ClientInfo()
diff --git a/google/api_core/gapic_v1/config.py b/google/api_core/gapic_v1/config.py
new file mode 100644
index 0000000..9c72287
--- /dev/null
+++ b/google/api_core/gapic_v1/config.py
@@ -0,0 +1,166 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helpers for loading gapic configuration data.
+
+The Google API generator creates supplementary configuration for each RPC
+method to tell the client library how to deal with retries and timeouts.
+"""
+
+import collections
+
+import grpc
+
+from google.api_core import exceptions
+from google.api_core import retry
+from google.api_core import timeout
+
+
+_MILLIS_PER_SECOND = 1000.0
+
+
+def _exception_class_for_grpc_status_name(name):
+    """Returns the Google API exception class for a gRPC error code name.
+
+    Args:
+        name (str): The name of the gRPC status code, for example,
+            ``UNAVAILABLE``.
+
+    Returns:
+        :func:`type`: The appropriate subclass of
+            :class:`google.api_core.exceptions.GoogleAPICallError`.
+    """
+    return exceptions.exception_class_for_grpc_status(getattr(grpc.StatusCode, name))
+
+
+def _retry_from_retry_config(retry_params, retry_codes, retry_impl=retry.Retry):
+    """Creates a Retry object given a gapic retry configuration.
+
+    Args:
+        retry_params (dict): The retry parameter values, for example::
+
+            {
+                "initial_retry_delay_millis": 1000,
+                "retry_delay_multiplier": 2.5,
+                "max_retry_delay_millis": 120000,
+                "initial_rpc_timeout_millis": 120000,
+                "rpc_timeout_multiplier": 1.0,
+                "max_rpc_timeout_millis": 120000,
+                "total_timeout_millis": 600000
+            }
+
+        retry_codes (sequence[str]): The list of retryable gRPC error code
+            names.
+
+    Returns:
+        google.api_core.retry.Retry: The default retry object for the method.
+    """
+    exception_classes = [
+        _exception_class_for_grpc_status_name(code) for code in retry_codes
+    ]
+    return retry_impl(
+        retry.if_exception_type(*exception_classes),
+        initial=(retry_params["initial_retry_delay_millis"] / _MILLIS_PER_SECOND),
+        maximum=(retry_params["max_retry_delay_millis"] / _MILLIS_PER_SECOND),
+        multiplier=retry_params["retry_delay_multiplier"],
+        deadline=retry_params["total_timeout_millis"] / _MILLIS_PER_SECOND,
+    )
+
+
+def _timeout_from_retry_config(retry_params):
+    """Creates a ExponentialTimeout object given a gapic retry configuration.
+
+    Args:
+        retry_params (dict): The retry parameter values, for example::
+
+            {
+                "initial_retry_delay_millis": 1000,
+                "retry_delay_multiplier": 2.5,
+                "max_retry_delay_millis": 120000,
+                "initial_rpc_timeout_millis": 120000,
+                "rpc_timeout_multiplier": 1.0,
+                "max_rpc_timeout_millis": 120000,
+                "total_timeout_millis": 600000
+            }
+
+    Returns:
+        google.api_core.retry.ExponentialTimeout: The default time object for
+            the method.
+    """
+    return timeout.ExponentialTimeout(
+        initial=(retry_params["initial_rpc_timeout_millis"] / _MILLIS_PER_SECOND),
+        maximum=(retry_params["max_rpc_timeout_millis"] / _MILLIS_PER_SECOND),
+        multiplier=retry_params["rpc_timeout_multiplier"],
+        deadline=(retry_params["total_timeout_millis"] / _MILLIS_PER_SECOND),
+    )
+
+
+MethodConfig = collections.namedtuple("MethodConfig", ["retry", "timeout"])
+
+
+def parse_method_configs(interface_config, retry_impl=retry.Retry):
+    """Creates default retry and timeout objects for each method in a gapic
+    interface config.
+
+    Args:
+        interface_config (Mapping): The interface config section of the full
+            gapic library config. For example, If the full configuration has
+            an interface named ``google.example.v1.ExampleService`` you would
+            pass in just that interface's configuration, for example
+            ``gapic_config['interfaces']['google.example.v1.ExampleService']``.
+        retry_impl (Callable): The constructor that creates a retry decorator
+            that will be applied to the method based on method configs.
+
+    Returns:
+        Mapping[str, MethodConfig]: A mapping of RPC method names to their
+            configuration.
+    """
+    # Grab all the retry codes
+    retry_codes_map = {
+        name: retry_codes
+        for name, retry_codes in interface_config.get("retry_codes", {}).items()
+    }
+
+    # Grab all of the retry params
+    retry_params_map = {
+        name: retry_params
+        for name, retry_params in interface_config.get("retry_params", {}).items()
+    }
+
+    # Iterate through all the API methods and create a flat MethodConfig
+    # instance for each one.
+    method_configs = {}
+
+    for method_name, method_params in interface_config.get("methods", {}).items():
+        retry_params_name = method_params.get("retry_params_name")
+
+        if retry_params_name is not None:
+            retry_params = retry_params_map[retry_params_name]
+            retry_ = _retry_from_retry_config(
+                retry_params,
+                retry_codes_map[method_params["retry_codes_name"]],
+                retry_impl,
+            )
+            timeout_ = _timeout_from_retry_config(retry_params)
+
+        # No retry config, so this is a non-retryable method.
+        else:
+            retry_ = None
+            timeout_ = timeout.ConstantTimeout(
+                method_params["timeout_millis"] / _MILLIS_PER_SECOND
+            )
+
+        method_configs[method_name] = MethodConfig(retry=retry_, timeout=timeout_)
+
+    return method_configs
diff --git a/google/api_core/gapic_v1/config_async.py b/google/api_core/gapic_v1/config_async.py
new file mode 100644
index 0000000..13d6a48
--- /dev/null
+++ b/google/api_core/gapic_v1/config_async.py
@@ -0,0 +1,42 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""AsyncIO helpers for loading gapic configuration data.
+
+The Google API generator creates supplementary configuration for each RPC
+method to tell the client library how to deal with retries and timeouts.
+"""
+
+from google.api_core import retry_async
+from google.api_core.gapic_v1 import config
+from google.api_core.gapic_v1.config import MethodConfig  # noqa: F401
+
+
+def parse_method_configs(interface_config):
+    """Creates default retry and timeout objects for each method in a gapic
+    interface config with AsyncIO semantics.
+
+    Args:
+        interface_config (Mapping): The interface config section of the full
+            gapic library config. For example, If the full configuration has
+            an interface named ``google.example.v1.ExampleService`` you would
+            pass in just that interface's configuration, for example
+            ``gapic_config['interfaces']['google.example.v1.ExampleService']``.
+
+    Returns:
+        Mapping[str, MethodConfig]: A mapping of RPC method names to their
+            configuration.
+    """
+    return config.parse_method_configs(
+        interface_config, retry_impl=retry_async.AsyncRetry
+    )
diff --git a/google/api_core/gapic_v1/method.py b/google/api_core/gapic_v1/method.py
new file mode 100644
index 0000000..73c8d4b
--- /dev/null
+++ b/google/api_core/gapic_v1/method.py
@@ -0,0 +1,253 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helpers for wrapping low-level gRPC methods with common functionality.
+
+This is used by gapic clients to provide common error mapping, retry, timeout,
+pagination, and long-running operations to gRPC methods.
+"""
+
+import enum
+import functools
+
+from google.api_core import grpc_helpers
+from google.api_core import timeout
+from google.api_core.gapic_v1 import client_info
+
+USE_DEFAULT_METADATA = object()
+
+
+class _MethodDefault(enum.Enum):
+    # Uses enum so that pytype/mypy knows that this is the only possible value.
+    # https://stackoverflow.com/a/60605919/101923
+    #
+    # Literal[_DEFAULT_VALUE] is an alternative, but only added in Python 3.8.
+    # https://docs.python.org/3/library/typing.html#typing.Literal
+    _DEFAULT_VALUE = object()
+
+
+DEFAULT = _MethodDefault._DEFAULT_VALUE
+"""Sentinel value indicating that a retry or timeout argument was unspecified,
+so the default should be used."""
+
+
+def _is_not_none_or_false(value):
+    return value is not None and value is not False
+
+
+def _apply_decorators(func, decorators):
+    """Apply a list of decorators to a given function.
+
+    ``decorators`` may contain items that are ``None`` or ``False`` which will
+    be ignored.
+    """
+    decorators = filter(_is_not_none_or_false, reversed(decorators))
+
+    for decorator in decorators:
+        func = decorator(func)
+
+    return func
+
+
+def _determine_timeout(default_timeout, specified_timeout, retry):
+    """Determines how timeout should be applied to a wrapped method.
+
+    Args:
+        default_timeout (Optional[Timeout]): The default timeout specified
+            at method creation time.
+        specified_timeout (Optional[Timeout]): The timeout specified at
+            invocation time. If :attr:`DEFAULT`, this will be set to
+            the ``default_timeout``.
+        retry (Optional[Retry]): The retry specified at invocation time.
+
+    Returns:
+        Optional[Timeout]: The timeout to apply to the method or ``None``.
+    """
+    # If timeout is specified as a number instead of a Timeout instance,
+    # convert it to a ConstantTimeout.
+    if isinstance(specified_timeout, (int, float)):
+        specified_timeout = timeout.ConstantTimeout(specified_timeout)
+    if isinstance(default_timeout, (int, float)):
+        default_timeout = timeout.ConstantTimeout(default_timeout)
+
+    if specified_timeout is DEFAULT:
+        specified_timeout = default_timeout
+
+    if specified_timeout is default_timeout:
+        # If timeout is the default and the default timeout is exponential and
+        # a non-default retry is specified, make sure the timeout's deadline
+        # matches the retry's. This handles the case where the user leaves
+        # the timeout default but specifies a lower deadline via the retry.
+        if (
+            retry
+            and retry is not DEFAULT
+            and isinstance(default_timeout, timeout.ExponentialTimeout)
+        ):
+            return default_timeout.with_deadline(retry._deadline)
+        else:
+            return default_timeout
+
+    return specified_timeout
+
+
+class _GapicCallable(object):
+    """Callable that applies retry, timeout, and metadata logic.
+
+    Args:
+        target (Callable): The low-level RPC method.
+        retry (google.api_core.retry.Retry): The default retry for the
+            callable. If ``None``, this callable will not retry by default
+        timeout (google.api_core.timeout.Timeout): The default timeout
+            for the callable. If ``None``, this callable will not specify
+            a timeout argument to the low-level RPC method by default.
+        metadata (Sequence[Tuple[str, str]]): Additional metadata that is
+            provided to the RPC method on every invocation. This is merged with
+            any metadata specified during invocation. If ``None``, no
+            additional metadata will be passed to the RPC method.
+    """
+
+    def __init__(self, target, retry, timeout, metadata=None):
+        self._target = target
+        self._retry = retry
+        self._timeout = timeout
+        self._metadata = metadata
+
+    def __call__(self, *args, timeout=DEFAULT, retry=DEFAULT, **kwargs):
+        """Invoke the low-level RPC with retry, timeout, and metadata."""
+        timeout = _determine_timeout(
+            self._timeout,
+            timeout,
+            # Use only the invocation-specified retry only for this, as we only
+            # want to adjust the timeout deadline if the *user* specified
+            # a different retry.
+            retry,
+        )
+
+        if retry is DEFAULT:
+            retry = self._retry
+
+        # Apply all applicable decorators.
+        wrapped_func = _apply_decorators(self._target, [retry, timeout])
+
+        # Add the user agent metadata to the call.
+        if self._metadata is not None:
+            metadata = kwargs.get("metadata", [])
+            # Due to the nature of invocation, None should be treated the same
+            # as not specified.
+            if metadata is None:
+                metadata = []
+            metadata = list(metadata)
+            metadata.extend(self._metadata)
+            kwargs["metadata"] = metadata
+
+        return wrapped_func(*args, **kwargs)
+
+
+def wrap_method(
+    func,
+    default_retry=None,
+    default_timeout=None,
+    client_info=client_info.DEFAULT_CLIENT_INFO,
+):
+    """Wrap an RPC method with common behavior.
+
+    This applies common error wrapping, retry, and timeout behavior a function.
+    The wrapped function will take optional ``retry`` and ``timeout``
+    arguments.
+
+    For example::
+
+        import google.api_core.gapic_v1.method
+        from google.api_core import retry
+        from google.api_core import timeout
+
+        # The original RPC method.
+        def get_topic(name, timeout=None):
+            request = publisher_v2.GetTopicRequest(name=name)
+            return publisher_stub.GetTopic(request, timeout=timeout)
+
+        default_retry = retry.Retry(deadline=60)
+        default_timeout = timeout.Timeout(deadline=60)
+        wrapped_get_topic = google.api_core.gapic_v1.method.wrap_method(
+            get_topic, default_retry)
+
+        # Execute get_topic with default retry and timeout:
+        response = wrapped_get_topic()
+
+        # Execute get_topic without doing any retying but with the default
+        # timeout:
+        response = wrapped_get_topic(retry=None)
+
+        # Execute get_topic but only retry on 5xx errors:
+        my_retry = retry.Retry(retry.if_exception_type(
+            exceptions.InternalServerError))
+        response = wrapped_get_topic(retry=my_retry)
+
+    The way this works is by late-wrapping the given function with the retry
+    and timeout decorators. Essentially, when ``wrapped_get_topic()`` is
+    called:
+
+    * ``get_topic()`` is first wrapped with the ``timeout`` into
+      ``get_topic_with_timeout``.
+    * ``get_topic_with_timeout`` is wrapped with the ``retry`` into
+      ``get_topic_with_timeout_and_retry()``.
+    * The final ``get_topic_with_timeout_and_retry`` is called passing through
+      the ``args``  and ``kwargs``.
+
+    The callstack is therefore::
+
+        method.__call__() ->
+            Retry.__call__() ->
+                Timeout.__call__() ->
+                    wrap_errors() ->
+                        get_topic()
+
+    Note that if ``timeout`` or ``retry`` is ``None``, then they are not
+    applied to the function. For example,
+    ``wrapped_get_topic(timeout=None, retry=None)`` is more or less
+    equivalent to just calling ``get_topic`` but with error re-mapping.
+
+    Args:
+        func (Callable[Any]): The function to wrap. It should accept an
+            optional ``timeout`` argument. If ``metadata`` is not ``None``, it
+            should accept a ``metadata`` argument.
+        default_retry (Optional[google.api_core.Retry]): The default retry
+            strategy. If ``None``, the method will not retry by default.
+        default_timeout (Optional[google.api_core.Timeout]): The default
+            timeout strategy. Can also be specified as an int or float. If
+            ``None``, the method will not have timeout specified by default.
+        client_info
+            (Optional[google.api_core.gapic_v1.client_info.ClientInfo]):
+                Client information used to create a user-agent string that's
+                passed as gRPC metadata to the method. If unspecified, then
+                a sane default will be used. If ``None``, then no user agent
+                metadata will be provided to the RPC method.
+
+    Returns:
+        Callable: A new callable that takes optional ``retry`` and ``timeout``
+            arguments and applies the common error mapping, retry, timeout,
+            and metadata behavior to the low-level RPC method.
+    """
+    func = grpc_helpers.wrap_errors(func)
+
+    if client_info is not None:
+        user_agent_metadata = [client_info.to_grpc_metadata()]
+    else:
+        user_agent_metadata = None
+
+    return functools.wraps(func)(
+        _GapicCallable(
+            func, default_retry, default_timeout, metadata=user_agent_metadata
+        )
+    )
diff --git a/google/api_core/gapic_v1/method_async.py b/google/api_core/gapic_v1/method_async.py
new file mode 100644
index 0000000..84c99aa
--- /dev/null
+++ b/google/api_core/gapic_v1/method_async.py
@@ -0,0 +1,48 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""AsyncIO helpers for wrapping gRPC methods with common functionality.
+
+This is used by gapic clients to provide common error mapping, retry, timeout,
+pagination, and long-running operations to gRPC methods.
+"""
+
+import functools
+
+from google.api_core import grpc_helpers_async
+from google.api_core.gapic_v1 import client_info
+from google.api_core.gapic_v1.method import _GapicCallable
+from google.api_core.gapic_v1.method import DEFAULT  # noqa: F401
+from google.api_core.gapic_v1.method import USE_DEFAULT_METADATA  # noqa: F401
+
+
+def wrap_method(
+    func,
+    default_retry=None,
+    default_timeout=None,
+    client_info=client_info.DEFAULT_CLIENT_INFO,
+):
+    """Wrap an async RPC method with common behavior.
+
+    Returns:
+        Callable: A new callable that takes optional ``retry`` and ``timeout``
+            arguments and applies the common error mapping, retry, timeout,
+            and metadata behavior to the low-level RPC method.
+    """
+    func = grpc_helpers_async.wrap_errors(func)
+
+    metadata = [client_info.to_grpc_metadata()] if client_info is not None else None
+
+    return functools.wraps(func)(
+        _GapicCallable(func, default_retry, default_timeout, metadata=metadata)
+    )
diff --git a/google/api_core/gapic_v1/routing_header.py b/google/api_core/gapic_v1/routing_header.py
new file mode 100644
index 0000000..a7bcb5a
--- /dev/null
+++ b/google/api_core/gapic_v1/routing_header.py
@@ -0,0 +1,57 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helpers for constructing routing headers.
+
+These headers are used by Google infrastructure to determine how to route
+requests, especially for services that are regional.
+
+Generally, these headers are specified as gRPC metadata.
+"""
+
+from urllib.parse import urlencode
+
+ROUTING_METADATA_KEY = "x-goog-request-params"
+
+
+def to_routing_header(params):
+    """Returns a routing header string for the given request parameters.
+
+    Args:
+        params (Mapping[str, Any]): A dictionary containing the request
+            parameters used for routing.
+
+    Returns:
+        str: The routing header string.
+    """
+    return urlencode(
+        params,
+        # Per Google API policy (go/api-url-encoding), / is not encoded.
+        safe="/",
+    )
+
+
+def to_grpc_metadata(params):
+    """Returns the gRPC metadata containing the routing headers for the given
+    request parameters.
+
+    Args:
+        params (Mapping[str, Any]): A dictionary containing the request
+            parameters used for routing.
+
+    Returns:
+        Tuple(str, str): The gRPC metadata containing the routing header key
+            and value.
+    """
+    return (ROUTING_METADATA_KEY, to_routing_header(params))
diff --git a/google/api_core/general_helpers.py b/google/api_core/general_helpers.py
new file mode 100644
index 0000000..fba7802
--- /dev/null
+++ b/google/api_core/general_helpers.py
@@ -0,0 +1,16 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# This import for backward compatibiltiy only.
+from functools import wraps  # noqa: F401 pragma: NO COVER
diff --git a/google/api_core/grpc_helpers.py b/google/api_core/grpc_helpers.py
new file mode 100644
index 0000000..594df98
--- /dev/null
+++ b/google/api_core/grpc_helpers.py
@@ -0,0 +1,495 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helpers for :mod:`grpc`."""
+
+import collections
+import functools
+
+import grpc
+import pkg_resources
+
+from google.api_core import exceptions
+import google.auth
+import google.auth.credentials
+import google.auth.transport.grpc
+import google.auth.transport.requests
+
+try:
+    import grpc_gcp
+
+    HAS_GRPC_GCP = True
+except ImportError:
+    HAS_GRPC_GCP = False
+
+try:
+    # google.auth.__version__ was added in 1.26.0
+    _GOOGLE_AUTH_VERSION = google.auth.__version__
+except AttributeError:
+    try:  # try pkg_resources if it is available
+        _GOOGLE_AUTH_VERSION = pkg_resources.get_distribution("google-auth").version
+    except pkg_resources.DistributionNotFound:  # pragma: NO COVER
+        _GOOGLE_AUTH_VERSION = None
+
+# The list of gRPC Callable interfaces that return iterators.
+_STREAM_WRAP_CLASSES = (grpc.UnaryStreamMultiCallable, grpc.StreamStreamMultiCallable)
+
+
+def _patch_callable_name(callable_):
+    """Fix-up gRPC callable attributes.
+
+    gRPC callable lack the ``__name__`` attribute which causes
+    :func:`functools.wraps` to error. This adds the attribute if needed.
+    """
+    if not hasattr(callable_, "__name__"):
+        callable_.__name__ = callable_.__class__.__name__
+
+
+def _wrap_unary_errors(callable_):
+    """Map errors for Unary-Unary and Stream-Unary gRPC callables."""
+    _patch_callable_name(callable_)
+
+    @functools.wraps(callable_)
+    def error_remapped_callable(*args, **kwargs):
+        try:
+            return callable_(*args, **kwargs)
+        except grpc.RpcError as exc:
+            raise exceptions.from_grpc_error(exc) from exc
+
+    return error_remapped_callable
+
+
+class _StreamingResponseIterator(grpc.Call):
+    def __init__(self, wrapped, prefetch_first_result=True):
+        self._wrapped = wrapped
+
+        # This iterator is used in a retry context, and returned outside after init.
+        # gRPC will not throw an exception until the stream is consumed, so we need
+        # to retrieve the first result, in order to fail, in order to trigger a retry.
+        try:
+            if prefetch_first_result:
+                self._stored_first_result = next(self._wrapped)
+        except TypeError:
+            # It is possible the wrapped method isn't an iterable (a grpc.Call
+            # for instance). If this happens don't store the first result.
+            pass
+        except StopIteration:
+            # ignore stop iteration at this time. This should be handled outside of retry.
+            pass
+
+    def __iter__(self):
+        """This iterator is also an iterable that returns itself."""
+        return self
+
+    def __next__(self):
+        """Get the next response from the stream.
+
+        Returns:
+            protobuf.Message: A single response from the stream.
+        """
+        try:
+            if hasattr(self, "_stored_first_result"):
+                result = self._stored_first_result
+                del self._stored_first_result
+                return result
+            return next(self._wrapped)
+        except grpc.RpcError as exc:
+            # If the stream has already returned data, we cannot recover here.
+            raise exceptions.from_grpc_error(exc) from exc
+
+    # grpc.Call & grpc.RpcContext interface
+
+    def add_callback(self, callback):
+        return self._wrapped.add_callback(callback)
+
+    def cancel(self):
+        return self._wrapped.cancel()
+
+    def code(self):
+        return self._wrapped.code()
+
+    def details(self):
+        return self._wrapped.details()
+
+    def initial_metadata(self):
+        return self._wrapped.initial_metadata()
+
+    def is_active(self):
+        return self._wrapped.is_active()
+
+    def time_remaining(self):
+        return self._wrapped.time_remaining()
+
+    def trailing_metadata(self):
+        return self._wrapped.trailing_metadata()
+
+
+def _wrap_stream_errors(callable_):
+    """Wrap errors for Unary-Stream and Stream-Stream gRPC callables.
+
+    The callables that return iterators require a bit more logic to re-map
+    errors when iterating. This wraps both the initial invocation and the
+    iterator of the return value to re-map errors.
+    """
+    _patch_callable_name(callable_)
+
+    @functools.wraps(callable_)
+    def error_remapped_callable(*args, **kwargs):
+        try:
+            result = callable_(*args, **kwargs)
+            # Auto-fetching the first result causes PubSub client's streaming pull
+            # to hang when re-opening the stream, thus we need examine the hacky
+            # hidden flag to see if pre-fetching is disabled.
+            # https://github.com/googleapis/python-pubsub/issues/93#issuecomment-630762257
+            prefetch_first = getattr(callable_, "_prefetch_first_result_", True)
+            return _StreamingResponseIterator(
+                result, prefetch_first_result=prefetch_first
+            )
+        except grpc.RpcError as exc:
+            raise exceptions.from_grpc_error(exc) from exc
+
+    return error_remapped_callable
+
+
+def wrap_errors(callable_):
+    """Wrap a gRPC callable and map :class:`grpc.RpcErrors` to friendly error
+    classes.
+
+    Errors raised by the gRPC callable are mapped to the appropriate
+    :class:`google.api_core.exceptions.GoogleAPICallError` subclasses.
+    The original `grpc.RpcError` (which is usually also a `grpc.Call`) is
+    available from the ``response`` property on the mapped exception. This
+    is useful for extracting metadata from the original error.
+
+    Args:
+        callable_ (Callable): A gRPC callable.
+
+    Returns:
+        Callable: The wrapped gRPC callable.
+    """
+    if isinstance(callable_, _STREAM_WRAP_CLASSES):
+        return _wrap_stream_errors(callable_)
+    else:
+        return _wrap_unary_errors(callable_)
+
+
+def _create_composite_credentials(
+    credentials=None,
+    credentials_file=None,
+    default_scopes=None,
+    scopes=None,
+    ssl_credentials=None,
+    quota_project_id=None,
+    default_host=None,
+):
+    """Create the composite credentials for secure channels.
+
+    Args:
+        credentials (google.auth.credentials.Credentials): The credentials. If
+            not specified, then this function will attempt to ascertain the
+            credentials from the environment using :func:`google.auth.default`.
+        credentials_file (str): A file with credentials that can be loaded with
+            :func:`google.auth.load_credentials_from_file`. This argument is
+            mutually exclusive with credentials.
+        default_scopes (Sequence[str]): A optional list of scopes needed for this
+            service. These are only used when credentials are not specified and
+            are passed to :func:`google.auth.default`.
+        scopes (Sequence[str]): A optional list of scopes needed for this
+            service. These are only used when credentials are not specified and
+            are passed to :func:`google.auth.default`.
+        ssl_credentials (grpc.ChannelCredentials): Optional SSL channel
+            credentials. This can be used to specify different certificates.
+        quota_project_id (str): An optional project to use for billing and quota.
+        default_host (str): The default endpoint. e.g., "pubsub.googleapis.com".
+
+    Returns:
+        grpc.ChannelCredentials: The composed channel credentials object.
+
+    Raises:
+        google.api_core.DuplicateCredentialArgs: If both a credentials object and credentials_file are passed.
+    """
+    if credentials and credentials_file:
+        raise exceptions.DuplicateCredentialArgs(
+            "'credentials' and 'credentials_file' are mutually exclusive."
+        )
+
+    if credentials_file:
+        credentials, _ = google.auth.load_credentials_from_file(
+            credentials_file, scopes=scopes, default_scopes=default_scopes
+        )
+    elif credentials:
+        credentials = google.auth.credentials.with_scopes_if_required(
+            credentials, scopes=scopes, default_scopes=default_scopes
+        )
+    else:
+        credentials, _ = google.auth.default(
+            scopes=scopes, default_scopes=default_scopes
+        )
+
+    if quota_project_id and isinstance(
+        credentials, google.auth.credentials.CredentialsWithQuotaProject
+    ):
+        credentials = credentials.with_quota_project(quota_project_id)
+
+    request = google.auth.transport.requests.Request()
+
+    # Create the metadata plugin for inserting the authorization header.
+    metadata_plugin = google.auth.transport.grpc.AuthMetadataPlugin(
+        credentials, request, default_host=default_host,
+    )
+
+    # Create a set of grpc.CallCredentials using the metadata plugin.
+    google_auth_credentials = grpc.metadata_call_credentials(metadata_plugin)
+
+    if ssl_credentials is None:
+        ssl_credentials = grpc.ssl_channel_credentials()
+
+    # Combine the ssl credentials and the authorization credentials.
+    return grpc.composite_channel_credentials(ssl_credentials, google_auth_credentials)
+
+
+def create_channel(
+    target,
+    credentials=None,
+    scopes=None,
+    ssl_credentials=None,
+    credentials_file=None,
+    quota_project_id=None,
+    default_scopes=None,
+    default_host=None,
+    **kwargs
+):
+    """Create a secure channel with credentials.
+
+    Args:
+        target (str): The target service address in the format 'hostname:port'.
+        credentials (google.auth.credentials.Credentials): The credentials. If
+            not specified, then this function will attempt to ascertain the
+            credentials from the environment using :func:`google.auth.default`.
+        scopes (Sequence[str]): A optional list of scopes needed for this
+            service. These are only used when credentials are not specified and
+            are passed to :func:`google.auth.default`.
+        ssl_credentials (grpc.ChannelCredentials): Optional SSL channel
+            credentials. This can be used to specify different certificates.
+        credentials_file (str): A file with credentials that can be loaded with
+            :func:`google.auth.load_credentials_from_file`. This argument is
+            mutually exclusive with credentials.
+        quota_project_id (str): An optional project to use for billing and quota.
+        default_scopes (Sequence[str]): Default scopes passed by a Google client
+            library. Use 'scopes' for user-defined scopes.
+        default_host (str): The default endpoint. e.g., "pubsub.googleapis.com".
+        kwargs: Additional key-word args passed to
+            :func:`grpc_gcp.secure_channel` or :func:`grpc.secure_channel`.
+
+    Returns:
+        grpc.Channel: The created channel.
+
+    Raises:
+        google.api_core.DuplicateCredentialArgs: If both a credentials object and credentials_file are passed.
+    """
+
+    composite_credentials = _create_composite_credentials(
+        credentials=credentials,
+        credentials_file=credentials_file,
+        default_scopes=default_scopes,
+        scopes=scopes,
+        ssl_credentials=ssl_credentials,
+        quota_project_id=quota_project_id,
+        default_host=default_host,
+    )
+
+    if HAS_GRPC_GCP:
+        # If grpc_gcp module is available use grpc_gcp.secure_channel,
+        # otherwise, use grpc.secure_channel to create grpc channel.
+        return grpc_gcp.secure_channel(target, composite_credentials, **kwargs)
+    else:
+        return grpc.secure_channel(target, composite_credentials, **kwargs)
+
+
+_MethodCall = collections.namedtuple(
+    "_MethodCall", ("request", "timeout", "metadata", "credentials")
+)
+
+_ChannelRequest = collections.namedtuple("_ChannelRequest", ("method", "request"))
+
+
+class _CallableStub(object):
+    """Stub for the grpc.*MultiCallable interfaces."""
+
+    def __init__(self, method, channel):
+        self._method = method
+        self._channel = channel
+        self.response = None
+        """Union[protobuf.Message, Callable[protobuf.Message], exception]:
+        The response to give when invoking this callable. If this is a
+        callable, it will be invoked with the request protobuf. If it's an
+        exception, the exception will be raised when this is invoked.
+        """
+        self.responses = None
+        """Iterator[
+            Union[protobuf.Message, Callable[protobuf.Message], exception]]:
+        An iterator of responses. If specified, self.response will be populated
+        on each invocation by calling ``next(self.responses)``."""
+        self.requests = []
+        """List[protobuf.Message]: All requests sent to this callable."""
+        self.calls = []
+        """List[Tuple]: All invocations of this callable. Each tuple is the
+        request, timeout, metadata, and credentials."""
+
+    def __call__(self, request, timeout=None, metadata=None, credentials=None):
+        self._channel.requests.append(_ChannelRequest(self._method, request))
+        self.calls.append(_MethodCall(request, timeout, metadata, credentials))
+        self.requests.append(request)
+
+        response = self.response
+        if self.responses is not None:
+            if response is None:
+                response = next(self.responses)
+            else:
+                raise ValueError(
+                    "{method}.response and {method}.responses are mutually "
+                    "exclusive.".format(method=self._method)
+                )
+
+        if callable(response):
+            return response(request)
+
+        if isinstance(response, Exception):
+            raise response
+
+        if response is not None:
+            return response
+
+        raise ValueError('Method stub for "{}" has no response.'.format(self._method))
+
+
+def _simplify_method_name(method):
+    """Simplifies a gRPC method name.
+
+    When gRPC invokes the channel to create a callable, it gives a full
+    method name like "/google.pubsub.v1.Publisher/CreateTopic". This
+    returns just the name of the method, in this case "CreateTopic".
+
+    Args:
+        method (str): The name of the method.
+
+    Returns:
+        str: The simplified name of the method.
+    """
+    return method.rsplit("/", 1).pop()
+
+
+class ChannelStub(grpc.Channel):
+    """A testing stub for the grpc.Channel interface.
+
+    This can be used to test any client that eventually uses a gRPC channel
+    to communicate. By passing in a channel stub, you can configure which
+    responses are returned and track which requests are made.
+
+    For example:
+
+    .. code-block:: python
+
+        channel_stub = grpc_helpers.ChannelStub()
+        client = FooClient(channel=channel_stub)
+
+        channel_stub.GetFoo.response = foo_pb2.Foo(name='bar')
+
+        foo = client.get_foo(labels=['baz'])
+
+        assert foo.name == 'bar'
+        assert channel_stub.GetFoo.requests[0].labels = ['baz']
+
+    Each method on the stub can be accessed and configured on the channel.
+    Here's some examples of various configurations:
+
+    .. code-block:: python
+
+        # Return a basic response:
+
+        channel_stub.GetFoo.response = foo_pb2.Foo(name='bar')
+        assert client.get_foo().name == 'bar'
+
+        # Raise an exception:
+        channel_stub.GetFoo.response = NotFound('...')
+
+        with pytest.raises(NotFound):
+            client.get_foo()
+
+        # Use a sequence of responses:
+        channel_stub.GetFoo.responses = iter([
+            foo_pb2.Foo(name='bar'),
+            foo_pb2.Foo(name='baz'),
+        ])
+
+        assert client.get_foo().name == 'bar'
+        assert client.get_foo().name == 'baz'
+
+        # Use a callable
+
+        def on_get_foo(request):
+            return foo_pb2.Foo(name='bar' + request.id)
+
+        channel_stub.GetFoo.response = on_get_foo
+
+        assert client.get_foo(id='123').name == 'bar123'
+    """
+
+    def __init__(self, responses=[]):
+        self.requests = []
+        """Sequence[Tuple[str, protobuf.Message]]: A list of all requests made
+        on this channel in order. The tuple is of method name, request
+        message."""
+        self._method_stubs = {}
+
+    def _stub_for_method(self, method):
+        method = _simplify_method_name(method)
+        self._method_stubs[method] = _CallableStub(method, self)
+        return self._method_stubs[method]
+
+    def __getattr__(self, key):
+        try:
+            return self._method_stubs[key]
+        except KeyError:
+            raise AttributeError
+
+    def unary_unary(self, method, request_serializer=None, response_deserializer=None):
+        """grpc.Channel.unary_unary implementation."""
+        return self._stub_for_method(method)
+
+    def unary_stream(self, method, request_serializer=None, response_deserializer=None):
+        """grpc.Channel.unary_stream implementation."""
+        return self._stub_for_method(method)
+
+    def stream_unary(self, method, request_serializer=None, response_deserializer=None):
+        """grpc.Channel.stream_unary implementation."""
+        return self._stub_for_method(method)
+
+    def stream_stream(
+        self, method, request_serializer=None, response_deserializer=None
+    ):
+        """grpc.Channel.stream_stream implementation."""
+        return self._stub_for_method(method)
+
+    def subscribe(self, callback, try_to_connect=False):
+        """grpc.Channel.subscribe implementation."""
+        pass
+
+    def unsubscribe(self, callback):
+        """grpc.Channel.unsubscribe implementation."""
+        pass
+
+    def close(self):
+        """grpc.Channel.close implementation."""
+        pass
diff --git a/google/api_core/grpc_helpers_async.py b/google/api_core/grpc_helpers_async.py
new file mode 100644
index 0000000..452e787
--- /dev/null
+++ b/google/api_core/grpc_helpers_async.py
@@ -0,0 +1,297 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""AsyncIO helpers for :mod:`grpc` supporting 3.6+.
+
+Please combine more detailed docstring in grpc_helpers.py to use following
+functions. This module is implementing the same surface with AsyncIO semantics.
+"""
+
+import asyncio
+import functools
+
+import grpc
+from grpc import aio
+
+from google.api_core import exceptions, grpc_helpers
+
+
+# TODO(lidiz) Support gRPC GCP wrapper
+HAS_GRPC_GCP = False
+
+# NOTE(lidiz) Alternatively, we can hack "__getattribute__" to perform
+# automatic patching for us. But that means the overhead of creating an
+# extra Python function spreads to every single send and receive.
+
+
+class _WrappedCall(aio.Call):
+    def __init__(self):
+        self._call = None
+
+    def with_call(self, call):
+        """Supplies the call object separately to keep __init__ clean."""
+        self._call = call
+        return self
+
+    async def initial_metadata(self):
+        return await self._call.initial_metadata()
+
+    async def trailing_metadata(self):
+        return await self._call.trailing_metadata()
+
+    async def code(self):
+        return await self._call.code()
+
+    async def details(self):
+        return await self._call.details()
+
+    def cancelled(self):
+        return self._call.cancelled()
+
+    def done(self):
+        return self._call.done()
+
+    def time_remaining(self):
+        return self._call.time_remaining()
+
+    def cancel(self):
+        return self._call.cancel()
+
+    def add_done_callback(self, callback):
+        self._call.add_done_callback(callback)
+
+    async def wait_for_connection(self):
+        try:
+            await self._call.wait_for_connection()
+        except grpc.RpcError as rpc_error:
+            raise exceptions.from_grpc_error(rpc_error) from rpc_error
+
+
+class _WrappedUnaryResponseMixin(_WrappedCall):
+    def __await__(self):
+        try:
+            response = yield from self._call.__await__()
+            return response
+        except grpc.RpcError as rpc_error:
+            raise exceptions.from_grpc_error(rpc_error) from rpc_error
+
+
+class _WrappedStreamResponseMixin(_WrappedCall):
+    def __init__(self):
+        self._wrapped_async_generator = None
+
+    async def read(self):
+        try:
+            return await self._call.read()
+        except grpc.RpcError as rpc_error:
+            raise exceptions.from_grpc_error(rpc_error) from rpc_error
+
+    async def _wrapped_aiter(self):
+        try:
+            # NOTE(lidiz) coverage doesn't understand the exception raised from
+            # __anext__ method. It is covered by test case:
+            #     test_wrap_stream_errors_aiter_non_rpc_error
+            async for response in self._call:  # pragma: no branch
+                yield response
+        except grpc.RpcError as rpc_error:
+            raise exceptions.from_grpc_error(rpc_error) from rpc_error
+
+    def __aiter__(self):
+        if not self._wrapped_async_generator:
+            self._wrapped_async_generator = self._wrapped_aiter()
+        return self._wrapped_async_generator
+
+
+class _WrappedStreamRequestMixin(_WrappedCall):
+    async def write(self, request):
+        try:
+            await self._call.write(request)
+        except grpc.RpcError as rpc_error:
+            raise exceptions.from_grpc_error(rpc_error) from rpc_error
+
+    async def done_writing(self):
+        try:
+            await self._call.done_writing()
+        except grpc.RpcError as rpc_error:
+            raise exceptions.from_grpc_error(rpc_error) from rpc_error
+
+
+# NOTE(lidiz) Implementing each individual class separately, so we don't
+# expose any API that should not be seen. E.g., __aiter__ in unary-unary
+# RPC, or __await__ in stream-stream RPC.
+class _WrappedUnaryUnaryCall(_WrappedUnaryResponseMixin, aio.UnaryUnaryCall):
+    """Wrapped UnaryUnaryCall to map exceptions."""
+
+
+class _WrappedUnaryStreamCall(_WrappedStreamResponseMixin, aio.UnaryStreamCall):
+    """Wrapped UnaryStreamCall to map exceptions."""
+
+
+class _WrappedStreamUnaryCall(
+    _WrappedUnaryResponseMixin, _WrappedStreamRequestMixin, aio.StreamUnaryCall
+):
+    """Wrapped StreamUnaryCall to map exceptions."""
+
+
+class _WrappedStreamStreamCall(
+    _WrappedStreamRequestMixin, _WrappedStreamResponseMixin, aio.StreamStreamCall
+):
+    """Wrapped StreamStreamCall to map exceptions."""
+
+
+def _wrap_unary_errors(callable_):
+    """Map errors for Unary-Unary async callables."""
+    grpc_helpers._patch_callable_name(callable_)
+
+    @functools.wraps(callable_)
+    def error_remapped_callable(*args, **kwargs):
+        call = callable_(*args, **kwargs)
+        return _WrappedUnaryUnaryCall().with_call(call)
+
+    return error_remapped_callable
+
+
+def _wrap_stream_errors(callable_):
+    """Map errors for streaming RPC async callables."""
+    grpc_helpers._patch_callable_name(callable_)
+
+    @functools.wraps(callable_)
+    async def error_remapped_callable(*args, **kwargs):
+        call = callable_(*args, **kwargs)
+
+        if isinstance(call, aio.UnaryStreamCall):
+            call = _WrappedUnaryStreamCall().with_call(call)
+        elif isinstance(call, aio.StreamUnaryCall):
+            call = _WrappedStreamUnaryCall().with_call(call)
+        elif isinstance(call, aio.StreamStreamCall):
+            call = _WrappedStreamStreamCall().with_call(call)
+        else:
+            raise TypeError("Unexpected type of call %s" % type(call))
+
+        await call.wait_for_connection()
+        return call
+
+    return error_remapped_callable
+
+
+def wrap_errors(callable_):
+    """Wrap a gRPC async callable and map :class:`grpc.RpcErrors` to
+    friendly error classes.
+
+    Errors raised by the gRPC callable are mapped to the appropriate
+    :class:`google.api_core.exceptions.GoogleAPICallError` subclasses. The
+    original `grpc.RpcError` (which is usually also a `grpc.Call`) is
+    available from the ``response`` property on the mapped exception. This
+    is useful for extracting metadata from the original error.
+
+    Args:
+        callable_ (Callable): A gRPC callable.
+
+    Returns: Callable: The wrapped gRPC callable.
+    """
+    if isinstance(callable_, aio.UnaryUnaryMultiCallable):
+        return _wrap_unary_errors(callable_)
+    else:
+        return _wrap_stream_errors(callable_)
+
+
+def create_channel(
+    target,
+    credentials=None,
+    scopes=None,
+    ssl_credentials=None,
+    credentials_file=None,
+    quota_project_id=None,
+    default_scopes=None,
+    default_host=None,
+    **kwargs
+):
+    """Create an AsyncIO secure channel with credentials.
+
+    Args:
+        target (str): The target service address in the format 'hostname:port'.
+        credentials (google.auth.credentials.Credentials): The credentials. If
+            not specified, then this function will attempt to ascertain the
+            credentials from the environment using :func:`google.auth.default`.
+        scopes (Sequence[str]): A optional list of scopes needed for this
+            service. These are only used when credentials are not specified and
+            are passed to :func:`google.auth.default`.
+        ssl_credentials (grpc.ChannelCredentials): Optional SSL channel
+            credentials. This can be used to specify different certificates.
+        credentials_file (str): A file with credentials that can be loaded with
+            :func:`google.auth.load_credentials_from_file`. This argument is
+            mutually exclusive with credentials.
+        quota_project_id (str): An optional project to use for billing and quota.
+        default_scopes (Sequence[str]): Default scopes passed by a Google client
+            library. Use 'scopes' for user-defined scopes.
+        default_host (str): The default endpoint. e.g., "pubsub.googleapis.com".
+        kwargs: Additional key-word args passed to :func:`aio.secure_channel`.
+
+    Returns:
+        aio.Channel: The created channel.
+
+    Raises:
+        google.api_core.DuplicateCredentialArgs: If both a credentials object and credentials_file are passed.
+    """
+
+    composite_credentials = grpc_helpers._create_composite_credentials(
+        credentials=credentials,
+        credentials_file=credentials_file,
+        scopes=scopes,
+        default_scopes=default_scopes,
+        ssl_credentials=ssl_credentials,
+        quota_project_id=quota_project_id,
+        default_host=default_host,
+    )
+
+    return aio.secure_channel(target, composite_credentials, **kwargs)
+
+
+class FakeUnaryUnaryCall(_WrappedUnaryUnaryCall):
+    """Fake implementation for unary-unary RPCs.
+
+    It is a dummy object for response message. Supply the intended response
+    upon the initialization, and the coroutine will return the exact response
+    message.
+    """
+
+    def __init__(self, response=object()):
+        self.response = response
+        self._future = asyncio.get_event_loop().create_future()
+        self._future.set_result(self.response)
+
+    def __await__(self):
+        response = yield from self._future.__await__()
+        return response
+
+
+class FakeStreamUnaryCall(_WrappedStreamUnaryCall):
+    """Fake implementation for stream-unary RPCs.
+
+    It is a dummy object for response message. Supply the intended response
+    upon the initialization, and the coroutine will return the exact response
+    message.
+    """
+
+    def __init__(self, response=object()):
+        self.response = response
+        self._future = asyncio.get_event_loop().create_future()
+        self._future.set_result(self.response)
+
+    def __await__(self):
+        response = yield from self._future.__await__()
+        return response
+
+    async def wait_for_connection(self):
+        pass
diff --git a/google/api_core/iam.py b/google/api_core/iam.py
new file mode 100644
index 0000000..4437c70
--- /dev/null
+++ b/google/api_core/iam.py
@@ -0,0 +1,427 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Non-API-specific IAM policy definitions
+
+For allowed roles / permissions, see:
+https://cloud.google.com/iam/docs/understanding-roles
+
+Example usage:
+
+.. code-block:: python
+
+   # ``get_iam_policy`` returns a :class:'~google.api_core.iam.Policy`.
+   policy = resource.get_iam_policy(requested_policy_version=3)
+
+   phred = "user:phred@example.com"
+   admin_group = "group:admins@groups.example.com"
+   account = "serviceAccount:account-1234@accounts.example.com"
+
+   policy.version = 3
+   policy.bindings = [
+       {
+           "role": "roles/owner",
+           "members": {phred, admin_group, account}
+       },
+       {
+           "role": "roles/editor",
+           "members": {"allAuthenticatedUsers"}
+       },
+       {
+           "role": "roles/viewer",
+           "members": {"allUsers"}
+           "condition": {
+               "title": "request_time",
+               "description": "Requests made before 2021-01-01T00:00:00Z",
+               "expression": "request.time < timestamp(\"2021-01-01T00:00:00Z\")"
+           }
+       }
+   ]
+
+   resource.set_iam_policy(policy)
+"""
+
+import collections
+import collections.abc
+import operator
+import warnings
+
+# Generic IAM roles
+
+OWNER_ROLE = "roles/owner"
+"""Generic role implying all rights to an object."""
+
+EDITOR_ROLE = "roles/editor"
+"""Generic role implying rights to modify an object."""
+
+VIEWER_ROLE = "roles/viewer"
+"""Generic role implying rights to access an object."""
+
+_ASSIGNMENT_DEPRECATED_MSG = """\
+Assigning to '{}' is deprecated. Use the `policy.bindings` property to modify bindings instead."""
+
+_DICT_ACCESS_MSG = """\
+Dict access is not supported on policies with version > 1 or with conditional bindings."""
+
+
+class InvalidOperationException(Exception):
+    """Raised when trying to use Policy class as a dict."""
+
+    pass
+
+
+class Policy(collections.abc.MutableMapping):
+    """IAM Policy
+
+    Args:
+        etag (Optional[str]): ETag used to identify a unique of the policy
+        version (Optional[int]): The syntax schema version of the policy.
+
+    Note:
+        Using conditions in bindings requires the policy's version to be set
+        to `3` or greater, depending on the versions that are currently supported.
+
+        Accessing the policy using dict operations will raise InvalidOperationException
+        when the policy's version is set to 3.
+
+        Use the policy.bindings getter/setter to retrieve and modify the policy's bindings.
+
+    See:
+        IAM Policy https://cloud.google.com/iam/reference/rest/v1/Policy
+        Policy versions https://cloud.google.com/iam/docs/policies#versions
+        Conditions overview https://cloud.google.com/iam/docs/conditions-overview.
+    """
+
+    _OWNER_ROLES = (OWNER_ROLE,)
+    """Roles mapped onto our ``owners`` attribute."""
+
+    _EDITOR_ROLES = (EDITOR_ROLE,)
+    """Roles mapped onto our ``editors`` attribute."""
+
+    _VIEWER_ROLES = (VIEWER_ROLE,)
+    """Roles mapped onto our ``viewers`` attribute."""
+
+    def __init__(self, etag=None, version=None):
+        self.etag = etag
+        self.version = version
+        self._bindings = []
+
+    def __iter__(self):
+        self.__check_version__()
+        # Exclude bindings with no members
+        return (binding["role"] for binding in self._bindings if binding["members"])
+
+    def __len__(self):
+        self.__check_version__()
+        # Exclude bindings with no members
+        return len(list(self.__iter__()))
+
+    def __getitem__(self, key):
+        self.__check_version__()
+        for b in self._bindings:
+            if b["role"] == key:
+                return b["members"]
+        # If the binding does not yet exist, create one
+        # NOTE: This will create bindings with no members
+        # which are ignored by __iter__ and __len__
+        new_binding = {"role": key, "members": set()}
+        self._bindings.append(new_binding)
+        return new_binding["members"]
+
+    def __setitem__(self, key, value):
+        self.__check_version__()
+        value = set(value)
+        for binding in self._bindings:
+            if binding["role"] == key:
+                binding["members"] = value
+                return
+        self._bindings.append({"role": key, "members": value})
+
+    def __delitem__(self, key):
+        self.__check_version__()
+        for b in self._bindings:
+            if b["role"] == key:
+                self._bindings.remove(b)
+                return
+        raise KeyError(key)
+
+    def __check_version__(self):
+        """Raise InvalidOperationException if version is greater than 1 or policy contains conditions."""
+        raise_version = self.version is not None and self.version > 1
+
+        if raise_version or self._contains_conditions():
+            raise InvalidOperationException(_DICT_ACCESS_MSG)
+
+    def _contains_conditions(self):
+        for b in self._bindings:
+            if b.get("condition") is not None:
+                return True
+        return False
+
+    @property
+    def bindings(self):
+        """The policy's list of bindings.
+
+        A binding is specified by a dictionary with keys:
+
+        * role (str): Role that is assigned to `members`.
+
+        * members (:obj:`set` of str): Specifies the identities associated to this binding.
+
+        * condition (:obj:`dict` of str:str): Specifies a condition under which this binding will apply.
+
+          * title (str): Title for the condition.
+
+          * description (:obj:str, optional): Description of the condition.
+
+          * expression: A CEL expression.
+
+        Type:
+           :obj:`list` of :obj:`dict`
+
+        See:
+           Policy versions https://cloud.google.com/iam/docs/policies#versions
+           Conditions overview https://cloud.google.com/iam/docs/conditions-overview.
+
+        Example:
+
+        .. code-block:: python
+
+           USER = "user:phred@example.com"
+           ADMIN_GROUP = "group:admins@groups.example.com"
+           SERVICE_ACCOUNT = "serviceAccount:account-1234@accounts.example.com"
+           CONDITION = {
+               "title": "request_time",
+               "description": "Requests made before 2021-01-01T00:00:00Z", # Optional
+               "expression": "request.time < timestamp(\"2021-01-01T00:00:00Z\")"
+           }
+
+           # Set policy's version to 3 before setting bindings containing conditions.
+           policy.version = 3
+
+           policy.bindings = [
+               {
+                   "role": "roles/viewer",
+                   "members": {USER, ADMIN_GROUP, SERVICE_ACCOUNT},
+                   "condition": CONDITION
+               },
+               ...
+           ]
+        """
+        return self._bindings
+
+    @bindings.setter
+    def bindings(self, bindings):
+        self._bindings = bindings
+
+    @property
+    def owners(self):
+        """Legacy access to owner role.
+
+        Raise InvalidOperationException if version is greater than 1 or policy contains conditions.
+
+        DEPRECATED:  use `policy.bindings` to access bindings instead.
+        """
+        result = set()
+        for role in self._OWNER_ROLES:
+            for member in self.get(role, ()):
+                result.add(member)
+        return frozenset(result)
+
+    @owners.setter
+    def owners(self, value):
+        """Update owners.
+
+        Raise InvalidOperationException if version is greater than 1 or policy contains conditions.
+
+        DEPRECATED:  use `policy.bindings` to access bindings instead.
+        """
+        warnings.warn(
+            _ASSIGNMENT_DEPRECATED_MSG.format("owners", OWNER_ROLE), DeprecationWarning
+        )
+        self[OWNER_ROLE] = value
+
+    @property
+    def editors(self):
+        """Legacy access to editor role.
+
+        Raise InvalidOperationException if version is greater than 1 or policy contains conditions.
+
+        DEPRECATED:  use `policy.bindings` to access bindings instead.
+        """
+        result = set()
+        for role in self._EDITOR_ROLES:
+            for member in self.get(role, ()):
+                result.add(member)
+        return frozenset(result)
+
+    @editors.setter
+    def editors(self, value):
+        """Update editors.
+
+        Raise InvalidOperationException if version is greater than 1 or policy contains conditions.
+
+        DEPRECATED:  use `policy.bindings` to modify bindings instead.
+        """
+        warnings.warn(
+            _ASSIGNMENT_DEPRECATED_MSG.format("editors", EDITOR_ROLE),
+            DeprecationWarning,
+        )
+        self[EDITOR_ROLE] = value
+
+    @property
+    def viewers(self):
+        """Legacy access to viewer role.
+
+        Raise InvalidOperationException if version is greater than 1 or policy contains conditions.
+
+        DEPRECATED:  use `policy.bindings` to modify bindings instead.
+        """
+        result = set()
+        for role in self._VIEWER_ROLES:
+            for member in self.get(role, ()):
+                result.add(member)
+        return frozenset(result)
+
+    @viewers.setter
+    def viewers(self, value):
+        """Update viewers.
+
+        Raise InvalidOperationException if version is greater than 1 or policy contains conditions.
+
+        DEPRECATED:  use `policy.bindings` to modify bindings instead.
+        """
+        warnings.warn(
+            _ASSIGNMENT_DEPRECATED_MSG.format("viewers", VIEWER_ROLE),
+            DeprecationWarning,
+        )
+        self[VIEWER_ROLE] = value
+
+    @staticmethod
+    def user(email):
+        """Factory method for a user member.
+
+        Args:
+            email (str): E-mail for this particular user.
+
+        Returns:
+            str: A member string corresponding to the given user.
+        """
+        return "user:%s" % (email,)
+
+    @staticmethod
+    def service_account(email):
+        """Factory method for a service account member.
+
+        Args:
+            email (str): E-mail for this particular service account.
+
+        Returns:
+            str: A member string corresponding to the given service account.
+
+        """
+        return "serviceAccount:%s" % (email,)
+
+    @staticmethod
+    def group(email):
+        """Factory method for a group member.
+
+        Args:
+            email (str): An id or e-mail for this particular group.
+
+        Returns:
+            str: A member string corresponding to the given group.
+        """
+        return "group:%s" % (email,)
+
+    @staticmethod
+    def domain(domain):
+        """Factory method for a domain member.
+
+        Args:
+            domain (str): The domain for this member.
+
+        Returns:
+            str: A member string corresponding to the given domain.
+        """
+        return "domain:%s" % (domain,)
+
+    @staticmethod
+    def all_users():
+        """Factory method for a member representing all users.
+
+        Returns:
+            str: A member string representing all users.
+        """
+        return "allUsers"
+
+    @staticmethod
+    def authenticated_users():
+        """Factory method for a member representing all authenticated users.
+
+        Returns:
+            str: A member string representing all authenticated users.
+        """
+        return "allAuthenticatedUsers"
+
+    @classmethod
+    def from_api_repr(cls, resource):
+        """Factory: create a policy from a JSON resource.
+
+        Args:
+            resource (dict): policy resource returned by ``getIamPolicy`` API.
+
+        Returns:
+            :class:`Policy`: the parsed policy
+        """
+        version = resource.get("version")
+        etag = resource.get("etag")
+        policy = cls(etag, version)
+        policy.bindings = resource.get("bindings", [])
+
+        for binding in policy.bindings:
+            binding["members"] = set(binding.get("members", ()))
+
+        return policy
+
+    def to_api_repr(self):
+        """Render a JSON policy resource.
+
+        Returns:
+            dict: a resource to be passed to the ``setIamPolicy`` API.
+        """
+        resource = {}
+
+        if self.etag is not None:
+            resource["etag"] = self.etag
+
+        if self.version is not None:
+            resource["version"] = self.version
+
+        if self._bindings and len(self._bindings) > 0:
+            bindings = []
+            for binding in self._bindings:
+                members = binding.get("members")
+                if members:
+                    new_binding = {"role": binding["role"], "members": sorted(members)}
+                    condition = binding.get("condition")
+                    if condition:
+                        new_binding["condition"] = condition
+                    bindings.append(new_binding)
+
+            if bindings:
+                # Sort bindings by role
+                key = operator.itemgetter("role")
+                resource["bindings"] = sorted(bindings, key=key)
+
+        return resource
diff --git a/google/api_core/operation.py b/google/api_core/operation.py
new file mode 100644
index 0000000..b17f753
--- /dev/null
+++ b/google/api_core/operation.py
@@ -0,0 +1,351 @@
+# Copyright 2016 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Futures for long-running operations returned from Google Cloud APIs.
+
+These futures can be used to synchronously wait for the result of a
+long-running operation using :meth:`Operation.result`:
+
+
+.. code-block:: python
+
+    operation = my_api_client.long_running_method()
+    result = operation.result()
+
+Or asynchronously using callbacks and :meth:`Operation.add_done_callback`:
+
+.. code-block:: python
+
+    operation = my_api_client.long_running_method()
+
+    def my_callback(future):
+        result = future.result()
+
+    operation.add_done_callback(my_callback)
+
+"""
+
+import functools
+import threading
+
+from google.api_core import exceptions
+from google.api_core import protobuf_helpers
+from google.api_core.future import polling
+from google.longrunning import operations_pb2
+from google.protobuf import json_format
+from google.rpc import code_pb2
+
+
+class Operation(polling.PollingFuture):
+    """A Future for interacting with a Google API Long-Running Operation.
+
+    Args:
+        operation (google.longrunning.operations_pb2.Operation): The
+            initial operation.
+        refresh (Callable[[], ~.api_core.operation.Operation]): A callable that
+            returns the latest state of the operation.
+        cancel (Callable[[], None]): A callable that tries to cancel
+            the operation.
+        result_type (func:`type`): The protobuf type for the operation's
+            result.
+        metadata_type (func:`type`): The protobuf type for the operation's
+            metadata.
+        retry (google.api_core.retry.Retry): The retry configuration used
+            when polling. This can be used to control how often :meth:`done`
+            is polled. Regardless of the retry's ``deadline``, it will be
+            overridden by the ``timeout`` argument to :meth:`result`.
+    """
+
+    def __init__(
+        self,
+        operation,
+        refresh,
+        cancel,
+        result_type,
+        metadata_type=None,
+        retry=polling.DEFAULT_RETRY,
+    ):
+        super(Operation, self).__init__(retry=retry)
+        self._operation = operation
+        self._refresh = refresh
+        self._cancel = cancel
+        self._result_type = result_type
+        self._metadata_type = metadata_type
+        self._completion_lock = threading.Lock()
+        # Invoke this in case the operation came back already complete.
+        self._set_result_from_operation()
+
+    @property
+    def operation(self):
+        """google.longrunning.Operation: The current long-running operation."""
+        return self._operation
+
+    @property
+    def metadata(self):
+        """google.protobuf.Message: the current operation metadata."""
+        if not self._operation.HasField("metadata"):
+            return None
+
+        return protobuf_helpers.from_any_pb(
+            self._metadata_type, self._operation.metadata
+        )
+
+    @classmethod
+    def deserialize(self, payload):
+        """Deserialize a ``google.longrunning.Operation`` protocol buffer.
+
+        Args:
+            payload (bytes): A serialized operation protocol buffer.
+
+        Returns:
+            ~.operations_pb2.Operation: An Operation protobuf object.
+        """
+        return operations_pb2.Operation.FromString(payload)
+
+    def _set_result_from_operation(self):
+        """Set the result or exception from the operation if it is complete."""
+        # This must be done in a lock to prevent the polling thread
+        # and main thread from both executing the completion logic
+        # at the same time.
+        with self._completion_lock:
+            # If the operation isn't complete or if the result has already been
+            # set, do not call set_result/set_exception again.
+            # Note: self._result_set is set to True in set_result and
+            # set_exception, in case those methods are invoked directly.
+            if not self._operation.done or self._result_set:
+                return
+
+            if self._operation.HasField("response"):
+                response = protobuf_helpers.from_any_pb(
+                    self._result_type, self._operation.response
+                )
+                self.set_result(response)
+            elif self._operation.HasField("error"):
+                exception = exceptions.from_grpc_status(
+                    status_code=self._operation.error.code,
+                    message=self._operation.error.message,
+                    errors=(self._operation.error,),
+                    response=self._operation,
+                )
+                self.set_exception(exception)
+            else:
+                exception = exceptions.GoogleAPICallError(
+                    "Unexpected state: Long-running operation had neither "
+                    "response nor error set."
+                )
+                self.set_exception(exception)
+
+    def _refresh_and_update(self, retry=polling.DEFAULT_RETRY):
+        """Refresh the operation and update the result if needed.
+
+        Args:
+            retry (google.api_core.retry.Retry): (Optional) How to retry the RPC.
+        """
+        # If the currently cached operation is done, no need to make another
+        # RPC as it will not change once done.
+        if not self._operation.done:
+            self._operation = self._refresh(retry=retry)
+            self._set_result_from_operation()
+
+    def done(self, retry=polling.DEFAULT_RETRY):
+        """Checks to see if the operation is complete.
+
+        Args:
+            retry (google.api_core.retry.Retry): (Optional) How to retry the RPC.
+
+        Returns:
+            bool: True if the operation is complete, False otherwise.
+        """
+        self._refresh_and_update(retry)
+        return self._operation.done
+
+    def cancel(self):
+        """Attempt to cancel the operation.
+
+        Returns:
+            bool: True if the cancel RPC was made, False if the operation is
+                already complete.
+        """
+        if self.done():
+            return False
+
+        self._cancel()
+        return True
+
+    def cancelled(self):
+        """True if the operation was cancelled."""
+        self._refresh_and_update()
+        return (
+            self._operation.HasField("error")
+            and self._operation.error.code == code_pb2.CANCELLED
+        )
+
+
+def _refresh_http(api_request, operation_name, retry=None):
+    """Refresh an operation using a JSON/HTTP client.
+
+    Args:
+        api_request (Callable): A callable used to make an API request. This
+            should generally be
+            :meth:`google.cloud._http.Connection.api_request`.
+        operation_name (str): The name of the operation.
+        retry (google.api_core.retry.Retry): (Optional) retry policy
+
+    Returns:
+        google.longrunning.operations_pb2.Operation: The operation.
+    """
+    path = "operations/{}".format(operation_name)
+
+    if retry is not None:
+        api_request = retry(api_request)
+
+    api_response = api_request(method="GET", path=path)
+    return json_format.ParseDict(api_response, operations_pb2.Operation())
+
+
+def _cancel_http(api_request, operation_name):
+    """Cancel an operation using a JSON/HTTP client.
+
+    Args:
+        api_request (Callable): A callable used to make an API request. This
+            should generally be
+            :meth:`google.cloud._http.Connection.api_request`.
+        operation_name (str): The name of the operation.
+    """
+    path = "operations/{}:cancel".format(operation_name)
+    api_request(method="POST", path=path)
+
+
+def from_http_json(operation, api_request, result_type, **kwargs):
+    """Create an operation future using a HTTP/JSON client.
+
+    This interacts with the long-running operations `service`_ (specific
+    to a given API) via `HTTP/JSON`_.
+
+    .. _HTTP/JSON: https://cloud.google.com/speech/reference/rest/\
+            v1beta1/operations#Operation
+
+    Args:
+        operation (dict): Operation as a dictionary.
+        api_request (Callable): A callable used to make an API request. This
+            should generally be
+            :meth:`google.cloud._http.Connection.api_request`.
+        result_type (:func:`type`): The protobuf result type.
+        kwargs: Keyword args passed into the :class:`Operation` constructor.
+
+    Returns:
+        ~.api_core.operation.Operation: The operation future to track the given
+            operation.
+    """
+    operation_proto = json_format.ParseDict(operation, operations_pb2.Operation())
+    refresh = functools.partial(_refresh_http, api_request, operation_proto.name)
+    cancel = functools.partial(_cancel_http, api_request, operation_proto.name)
+    return Operation(operation_proto, refresh, cancel, result_type, **kwargs)
+
+
+def _refresh_grpc(operations_stub, operation_name, retry=None):
+    """Refresh an operation using a gRPC client.
+
+    Args:
+        operations_stub (google.longrunning.operations_pb2.OperationsStub):
+            The gRPC operations stub.
+        operation_name (str): The name of the operation.
+        retry (google.api_core.retry.Retry): (Optional) retry policy
+
+    Returns:
+        google.longrunning.operations_pb2.Operation: The operation.
+    """
+    request_pb = operations_pb2.GetOperationRequest(name=operation_name)
+
+    rpc = operations_stub.GetOperation
+    if retry is not None:
+        rpc = retry(rpc)
+
+    return rpc(request_pb)
+
+
+def _cancel_grpc(operations_stub, operation_name):
+    """Cancel an operation using a gRPC client.
+
+    Args:
+        operations_stub (google.longrunning.operations_pb2.OperationsStub):
+            The gRPC operations stub.
+        operation_name (str): The name of the operation.
+    """
+    request_pb = operations_pb2.CancelOperationRequest(name=operation_name)
+    operations_stub.CancelOperation(request_pb)
+
+
+def from_grpc(operation, operations_stub, result_type, grpc_metadata=None, **kwargs):
+    """Create an operation future using a gRPC client.
+
+    This interacts with the long-running operations `service`_ (specific
+    to a given API) via gRPC.
+
+    .. _service: https://github.com/googleapis/googleapis/blob/\
+                 050400df0fdb16f63b63e9dee53819044bffc857/\
+                 google/longrunning/operations.proto#L38
+
+    Args:
+        operation (google.longrunning.operations_pb2.Operation): The operation.
+        operations_stub (google.longrunning.operations_pb2.OperationsStub):
+            The operations stub.
+        result_type (:func:`type`): The protobuf result type.
+        grpc_metadata (Optional[List[Tuple[str, str]]]): Additional metadata to pass
+            to the rpc.
+        kwargs: Keyword args passed into the :class:`Operation` constructor.
+
+    Returns:
+        ~.api_core.operation.Operation: The operation future to track the given
+            operation.
+    """
+    refresh = functools.partial(
+        _refresh_grpc, operations_stub, operation.name, metadata=grpc_metadata
+    )
+    cancel = functools.partial(
+        _cancel_grpc, operations_stub, operation.name, metadata=grpc_metadata
+    )
+    return Operation(operation, refresh, cancel, result_type, **kwargs)
+
+
+def from_gapic(operation, operations_client, result_type, grpc_metadata=None, **kwargs):
+    """Create an operation future from a gapic client.
+
+    This interacts with the long-running operations `service`_ (specific
+    to a given API) via a gapic client.
+
+    .. _service: https://github.com/googleapis/googleapis/blob/\
+                 050400df0fdb16f63b63e9dee53819044bffc857/\
+                 google/longrunning/operations.proto#L38
+
+    Args:
+        operation (google.longrunning.operations_pb2.Operation): The operation.
+        operations_client (google.api_core.operations_v1.OperationsClient):
+            The operations client.
+        result_type (:func:`type`): The protobuf result type.
+        grpc_metadata (Optional[List[Tuple[str, str]]]): Additional metadata to pass
+            to the rpc.
+        kwargs: Keyword args passed into the :class:`Operation` constructor.
+
+    Returns:
+        ~.api_core.operation.Operation: The operation future to track the given
+            operation.
+    """
+    refresh = functools.partial(
+        operations_client.get_operation, operation.name, metadata=grpc_metadata
+    )
+    cancel = functools.partial(
+        operations_client.cancel_operation, operation.name, metadata=grpc_metadata
+    )
+    return Operation(operation, refresh, cancel, result_type, **kwargs)
diff --git a/google/api_core/operation_async.py b/google/api_core/operation_async.py
new file mode 100644
index 0000000..6bae865
--- /dev/null
+++ b/google/api_core/operation_async.py
@@ -0,0 +1,221 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""AsyncIO futures for long-running operations returned from Google Cloud APIs.
+
+These futures can be used to await for the result of a long-running operation
+using :meth:`AsyncOperation.result`:
+
+
+.. code-block:: python
+
+    operation = my_api_client.long_running_method()
+    result = await operation.result()
+
+Or asynchronously using callbacks and :meth:`Operation.add_done_callback`:
+
+.. code-block:: python
+
+    operation = my_api_client.long_running_method()
+
+    def my_callback(future):
+        result = await future.result()
+
+    operation.add_done_callback(my_callback)
+
+"""
+
+import functools
+import threading
+
+from google.api_core import exceptions
+from google.api_core import protobuf_helpers
+from google.api_core.future import async_future
+from google.longrunning import operations_pb2
+from google.rpc import code_pb2
+
+
+class AsyncOperation(async_future.AsyncFuture):
+    """A Future for interacting with a Google API Long-Running Operation.
+
+    Args:
+        operation (google.longrunning.operations_pb2.Operation): The
+            initial operation.
+        refresh (Callable[[], ~.api_core.operation.Operation]): A callable that
+            returns the latest state of the operation.
+        cancel (Callable[[], None]): A callable that tries to cancel
+            the operation.
+        result_type (func:`type`): The protobuf type for the operation's
+            result.
+        metadata_type (func:`type`): The protobuf type for the operation's
+            metadata.
+        retry (google.api_core.retry.Retry): The retry configuration used
+            when polling. This can be used to control how often :meth:`done`
+            is polled. Regardless of the retry's ``deadline``, it will be
+            overridden by the ``timeout`` argument to :meth:`result`.
+    """
+
+    def __init__(
+        self,
+        operation,
+        refresh,
+        cancel,
+        result_type,
+        metadata_type=None,
+        retry=async_future.DEFAULT_RETRY,
+    ):
+        super().__init__(retry=retry)
+        self._operation = operation
+        self._refresh = refresh
+        self._cancel = cancel
+        self._result_type = result_type
+        self._metadata_type = metadata_type
+        self._completion_lock = threading.Lock()
+        # Invoke this in case the operation came back already complete.
+        self._set_result_from_operation()
+
+    @property
+    def operation(self):
+        """google.longrunning.Operation: The current long-running operation."""
+        return self._operation
+
+    @property
+    def metadata(self):
+        """google.protobuf.Message: the current operation metadata."""
+        if not self._operation.HasField("metadata"):
+            return None
+
+        return protobuf_helpers.from_any_pb(
+            self._metadata_type, self._operation.metadata
+        )
+
+    @classmethod
+    def deserialize(cls, payload):
+        """Deserialize a ``google.longrunning.Operation`` protocol buffer.
+
+        Args:
+            payload (bytes): A serialized operation protocol buffer.
+
+        Returns:
+            ~.operations_pb2.Operation: An Operation protobuf object.
+        """
+        return operations_pb2.Operation.FromString(payload)
+
+    def _set_result_from_operation(self):
+        """Set the result or exception from the operation if it is complete."""
+        # This must be done in a lock to prevent the async_future thread
+        # and main thread from both executing the completion logic
+        # at the same time.
+        with self._completion_lock:
+            # If the operation isn't complete or if the result has already been
+            # set, do not call set_result/set_exception again.
+            if not self._operation.done or self._future.done():
+                return
+
+            if self._operation.HasField("response"):
+                response = protobuf_helpers.from_any_pb(
+                    self._result_type, self._operation.response
+                )
+                self.set_result(response)
+            elif self._operation.HasField("error"):
+                exception = exceptions.GoogleAPICallError(
+                    self._operation.error.message,
+                    errors=(self._operation.error,),
+                    response=self._operation,
+                )
+                self.set_exception(exception)
+            else:
+                exception = exceptions.GoogleAPICallError(
+                    "Unexpected state: Long-running operation had neither "
+                    "response nor error set."
+                )
+                self.set_exception(exception)
+
+    async def _refresh_and_update(self, retry=async_future.DEFAULT_RETRY):
+        """Refresh the operation and update the result if needed.
+
+        Args:
+            retry (google.api_core.retry.Retry): (Optional) How to retry the RPC.
+        """
+        # If the currently cached operation is done, no need to make another
+        # RPC as it will not change once done.
+        if not self._operation.done:
+            self._operation = await self._refresh(retry=retry)
+            self._set_result_from_operation()
+
+    async def done(self, retry=async_future.DEFAULT_RETRY):
+        """Checks to see if the operation is complete.
+
+        Args:
+            retry (google.api_core.retry.Retry): (Optional) How to retry the RPC.
+
+        Returns:
+            bool: True if the operation is complete, False otherwise.
+        """
+        await self._refresh_and_update(retry)
+        return self._operation.done
+
+    async def cancel(self):
+        """Attempt to cancel the operation.
+
+        Returns:
+            bool: True if the cancel RPC was made, False if the operation is
+                already complete.
+        """
+        result = await self.done()
+        if result:
+            return False
+        else:
+            await self._cancel()
+            return True
+
+    async def cancelled(self):
+        """True if the operation was cancelled."""
+        await self._refresh_and_update()
+        return (
+            self._operation.HasField("error")
+            and self._operation.error.code == code_pb2.CANCELLED
+        )
+
+
+def from_gapic(operation, operations_client, result_type, grpc_metadata=None, **kwargs):
+    """Create an operation future from a gapic client.
+
+    This interacts with the long-running operations `service`_ (specific
+    to a given API) via a gapic client.
+
+    .. _service: https://github.com/googleapis/googleapis/blob/\
+                 050400df0fdb16f63b63e9dee53819044bffc857/\
+                 google/longrunning/operations.proto#L38
+
+    Args:
+        operation (google.longrunning.operations_pb2.Operation): The operation.
+        operations_client (google.api_core.operations_v1.OperationsClient):
+            The operations client.
+        result_type (:func:`type`): The protobuf result type.
+        grpc_metadata (Optional[List[Tuple[str, str]]]): Additional metadata to pass
+            to the rpc.
+        kwargs: Keyword args passed into the :class:`Operation` constructor.
+
+    Returns:
+        ~.api_core.operation.Operation: The operation future to track the given
+            operation.
+    """
+    refresh = functools.partial(
+        operations_client.get_operation, operation.name, metadata=grpc_metadata
+    )
+    cancel = functools.partial(
+        operations_client.cancel_operation, operation.name, metadata=grpc_metadata
+    )
+    return AsyncOperation(operation, refresh, cancel, result_type, **kwargs)
diff --git a/google/api_core/operations_v1/__init__.py b/google/api_core/operations_v1/__init__.py
new file mode 100644
index 0000000..6118645
--- /dev/null
+++ b/google/api_core/operations_v1/__init__.py
@@ -0,0 +1,27 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Package for interacting with the google.longrunning.operations meta-API."""
+
+from google.api_core.operations_v1.abstract_operations_client import AbstractOperationsClient
+from google.api_core.operations_v1.operations_async_client import OperationsAsyncClient
+from google.api_core.operations_v1.operations_client import OperationsClient
+from google.api_core.operations_v1.transports.rest import OperationsRestTransport
+
+__all__ = [
+    "AbstractOperationsClient",
+    "OperationsAsyncClient",
+    "OperationsClient",
+    "OperationsRestTransport"
+]
diff --git a/google/api_core/operations_v1/abstract_operations_client.py b/google/api_core/operations_v1/abstract_operations_client.py
new file mode 100644
index 0000000..631094e
--- /dev/null
+++ b/google/api_core/operations_v1/abstract_operations_client.py
@@ -0,0 +1,564 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+from collections import OrderedDict
+from distutils import util
+import os
+import re
+from typing import Dict, Optional, Sequence, Tuple, Type, Union
+
+from google.api_core import client_options as client_options_lib  # type: ignore
+from google.api_core import gapic_v1  # type: ignore
+from google.api_core import retry as retries  # type: ignore
+from google.api_core.operations_v1 import pagers
+from google.api_core.operations_v1.transports.base import (
+    DEFAULT_CLIENT_INFO,
+    OperationsTransport,
+)
+from google.api_core.operations_v1.transports.rest import OperationsRestTransport
+from google.auth import credentials as ga_credentials  # type: ignore
+from google.auth.exceptions import MutualTLSChannelError  # type: ignore
+from google.auth.transport import mtls  # type: ignore
+from google.longrunning import operations_pb2
+from google.oauth2 import service_account  # type: ignore
+
+OptionalRetry = Union[retries.Retry, object]
+
+
+class AbstractOperationsClientMeta(type):
+    """Metaclass for the Operations client.
+
+    This provides class-level methods for building and retrieving
+    support objects (e.g. transport) without polluting the client instance
+    objects.
+    """
+
+    _transport_registry = OrderedDict()  # type: Dict[str, Type[OperationsTransport]]
+    _transport_registry["rest"] = OperationsRestTransport
+
+    def get_transport_class(
+        cls, label: Optional[str] = None,
+    ) -> Type[OperationsTransport]:
+        """Returns an appropriate transport class.
+
+        Args:
+            label: The name of the desired transport. If none is
+                provided, then the first transport in the registry is used.
+
+        Returns:
+            The transport class to use.
+        """
+        # If a specific transport is requested, return that one.
+        if label:
+            return cls._transport_registry[label]
+
+        # No transport is requested; return the default (that is, the first one
+        # in the dictionary).
+        return next(iter(cls._transport_registry.values()))
+
+
+class AbstractOperationsClient(metaclass=AbstractOperationsClientMeta):
+    """Manages long-running operations with an API service.
+
+    When an API method normally takes long time to complete, it can be
+    designed to return [Operation][google.api_core.operations_v1.Operation] to the
+    client, and the client can use this interface to receive the real
+    response asynchronously by polling the operation resource, or pass
+    the operation resource to another API (such as Google Cloud Pub/Sub
+    API) to receive the response. Any API service that returns
+    long-running operations should implement the ``Operations``
+    interface so developers can have a consistent client experience.
+    """
+
+    @staticmethod
+    def _get_default_mtls_endpoint(api_endpoint):
+        """Converts api endpoint to mTLS endpoint.
+
+        Convert "*.sandbox.googleapis.com" and "*.googleapis.com" to
+        "*.mtls.sandbox.googleapis.com" and "*.mtls.googleapis.com" respectively.
+        Args:
+            api_endpoint (Optional[str]): the api endpoint to convert.
+        Returns:
+            str: converted mTLS api endpoint.
+        """
+        if not api_endpoint:
+            return api_endpoint
+
+        mtls_endpoint_re = re.compile(
+            r"(?P<name>[^.]+)(?P<mtls>\.mtls)?(?P<sandbox>\.sandbox)?(?P<googledomain>\.googleapis\.com)?"
+        )
+
+        m = mtls_endpoint_re.match(api_endpoint)
+        name, mtls, sandbox, googledomain = m.groups()
+        if mtls or not googledomain:
+            return api_endpoint
+
+        if sandbox:
+            return api_endpoint.replace(
+                "sandbox.googleapis.com", "mtls.sandbox.googleapis.com"
+            )
+
+        return api_endpoint.replace(".googleapis.com", ".mtls.googleapis.com")
+
+    DEFAULT_ENDPOINT = "longrunning.googleapis.com"
+    DEFAULT_MTLS_ENDPOINT = _get_default_mtls_endpoint.__func__(  # type: ignore
+        DEFAULT_ENDPOINT
+    )
+
+    @classmethod
+    def from_service_account_info(cls, info: dict, *args, **kwargs):
+        """Creates an instance of this client using the provided credentials
+            info.
+
+        Args:
+            info (dict): The service account private key info.
+            args: Additional arguments to pass to the constructor.
+            kwargs: Additional arguments to pass to the constructor.
+
+        Returns:
+            AbstractOperationsClient: The constructed client.
+        """
+        credentials = service_account.Credentials.from_service_account_info(info)
+        kwargs["credentials"] = credentials
+        return cls(*args, **kwargs)
+
+    @classmethod
+    def from_service_account_file(cls, filename: str, *args, **kwargs):
+        """Creates an instance of this client using the provided credentials
+            file.
+
+        Args:
+            filename (str): The path to the service account private key json
+                file.
+            args: Additional arguments to pass to the constructor.
+            kwargs: Additional arguments to pass to the constructor.
+
+        Returns:
+            AbstractOperationsClient: The constructed client.
+        """
+        credentials = service_account.Credentials.from_service_account_file(filename)
+        kwargs["credentials"] = credentials
+        return cls(*args, **kwargs)
+
+    from_service_account_json = from_service_account_file
+
+    @property
+    def transport(self) -> OperationsTransport:
+        """Returns the transport used by the client instance.
+
+        Returns:
+            OperationsTransport: The transport used by the client
+                instance.
+        """
+        return self._transport
+
+    @staticmethod
+    def common_billing_account_path(billing_account: str,) -> str:
+        """Returns a fully-qualified billing_account string."""
+        return "billingAccounts/{billing_account}".format(
+            billing_account=billing_account,
+        )
+
+    @staticmethod
+    def parse_common_billing_account_path(path: str) -> Dict[str, str]:
+        """Parse a billing_account path into its component segments."""
+        m = re.match(r"^billingAccounts/(?P<billing_account>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    @staticmethod
+    def common_folder_path(folder: str,) -> str:
+        """Returns a fully-qualified folder string."""
+        return "folders/{folder}".format(folder=folder,)
+
+    @staticmethod
+    def parse_common_folder_path(path: str) -> Dict[str, str]:
+        """Parse a folder path into its component segments."""
+        m = re.match(r"^folders/(?P<folder>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    @staticmethod
+    def common_organization_path(organization: str,) -> str:
+        """Returns a fully-qualified organization string."""
+        return "organizations/{organization}".format(organization=organization,)
+
+    @staticmethod
+    def parse_common_organization_path(path: str) -> Dict[str, str]:
+        """Parse a organization path into its component segments."""
+        m = re.match(r"^organizations/(?P<organization>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    @staticmethod
+    def common_project_path(project: str,) -> str:
+        """Returns a fully-qualified project string."""
+        return "projects/{project}".format(project=project,)
+
+    @staticmethod
+    def parse_common_project_path(path: str) -> Dict[str, str]:
+        """Parse a project path into its component segments."""
+        m = re.match(r"^projects/(?P<project>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    @staticmethod
+    def common_location_path(project: str, location: str,) -> str:
+        """Returns a fully-qualified location string."""
+        return "projects/{project}/locations/{location}".format(
+            project=project, location=location,
+        )
+
+    @staticmethod
+    def parse_common_location_path(path: str) -> Dict[str, str]:
+        """Parse a location path into its component segments."""
+        m = re.match(r"^projects/(?P<project>.+?)/locations/(?P<location>.+?)$", path)
+        return m.groupdict() if m else {}
+
+    def __init__(
+        self,
+        *,
+        credentials: Optional[ga_credentials.Credentials] = None,
+        transport: Union[str, OperationsTransport, None] = None,
+        client_options: Optional[client_options_lib.ClientOptions] = None,
+        client_info: gapic_v1.client_info.ClientInfo = DEFAULT_CLIENT_INFO,
+    ) -> None:
+        """Instantiates the operations client.
+
+        Args:
+            credentials (Optional[google.auth.credentials.Credentials]): The
+                authorization credentials to attach to requests. These
+                credentials identify the application to the service; if none
+                are specified, the client will attempt to ascertain the
+                credentials from the environment.
+            transport (Union[str, OperationsTransport]): The
+                transport to use. If set to None, a transport is chosen
+                automatically.
+            client_options (google.api_core.client_options.ClientOptions): Custom options for the
+                client. It won't take effect if a ``transport`` instance is provided.
+                (1) The ``api_endpoint`` property can be used to override the
+                default endpoint provided by the client. GOOGLE_API_USE_MTLS_ENDPOINT
+                environment variable can also be used to override the endpoint:
+                "always" (always use the default mTLS endpoint), "never" (always
+                use the default regular endpoint) and "auto" (auto switch to the
+                default mTLS endpoint if client certificate is present, this is
+                the default value). However, the ``api_endpoint`` property takes
+                precedence if provided.
+                (2) If GOOGLE_API_USE_CLIENT_CERTIFICATE environment variable
+                is "true", then the ``client_cert_source`` property can be used
+                to provide client certificate for mutual TLS transport. If
+                not provided, the default SSL client certificate will be used if
+                present. If GOOGLE_API_USE_CLIENT_CERTIFICATE is "false" or not
+                set, no client certificate will be used.
+            client_info (google.api_core.gapic_v1.client_info.ClientInfo):
+                The client info used to send a user-agent string along with
+                API requests. If ``None``, then default info will be used.
+                Generally, you only need to set this if you're developing
+                your own client library.
+
+        Raises:
+            google.auth.exceptions.MutualTLSChannelError: If mutual TLS transport
+                creation failed for any reason.
+        """
+        if isinstance(client_options, dict):
+            client_options = client_options_lib.from_dict(client_options)
+        if client_options is None:
+            client_options = client_options_lib.ClientOptions()
+
+        # Create SSL credentials for mutual TLS if needed.
+        use_client_cert = bool(
+            util.strtobool(os.getenv("GOOGLE_API_USE_CLIENT_CERTIFICATE", "false"))
+        )
+
+        client_cert_source_func = None
+        is_mtls = False
+        if use_client_cert:
+            if client_options.client_cert_source:
+                is_mtls = True
+                client_cert_source_func = client_options.client_cert_source
+            else:
+                is_mtls = mtls.has_default_client_cert_source()
+                if is_mtls:
+                    client_cert_source_func = mtls.default_client_cert_source()
+                else:
+                    client_cert_source_func = None
+
+        # Figure out which api endpoint to use.
+        if client_options.api_endpoint is not None:
+            api_endpoint = client_options.api_endpoint
+        else:
+            use_mtls_env = os.getenv("GOOGLE_API_USE_MTLS_ENDPOINT", "auto")
+            if use_mtls_env == "never":
+                api_endpoint = self.DEFAULT_ENDPOINT
+            elif use_mtls_env == "always":
+                api_endpoint = self.DEFAULT_MTLS_ENDPOINT
+            elif use_mtls_env == "auto":
+                if is_mtls:
+                    api_endpoint = self.DEFAULT_MTLS_ENDPOINT
+                else:
+                    api_endpoint = self.DEFAULT_ENDPOINT
+            else:
+                raise MutualTLSChannelError(
+                    "Unsupported GOOGLE_API_USE_MTLS_ENDPOINT value. Accepted "
+                    "values: never, auto, always"
+                )
+
+        # Save or instantiate the transport.
+        # Ordinarily, we provide the transport, but allowing a custom transport
+        # instance provides an extensibility point for unusual situations.
+        if isinstance(transport, OperationsTransport):
+            # transport is a OperationsTransport instance.
+            if credentials or client_options.credentials_file:
+                raise ValueError(
+                    "When providing a transport instance, "
+                    "provide its credentials directly."
+                )
+            if client_options.scopes:
+                raise ValueError(
+                    "When providing a transport instance, provide its scopes "
+                    "directly."
+                )
+            self._transport = transport
+        else:
+            Transport = type(self).get_transport_class(transport)
+            self._transport = Transport(
+                credentials=credentials,
+                credentials_file=client_options.credentials_file,
+                host=api_endpoint,
+                scopes=client_options.scopes,
+                client_cert_source_for_mtls=client_cert_source_func,
+                quota_project_id=client_options.quota_project_id,
+                client_info=client_info,
+                always_use_jwt_access=True,
+            )
+
+    def list_operations(
+        self,
+        name: str,
+        filter_: Optional[str] = None,
+        *,
+        page_size: Optional[int] = None,
+        page_token: Optional[str] = None,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
+        timeout: Optional[float] = None,
+        metadata: Sequence[Tuple[str, str]] = (),
+    ) -> pagers.ListOperationsPager:
+        r"""Lists operations that match the specified filter in the request.
+        If the server doesn't support this method, it returns
+        ``UNIMPLEMENTED``.
+
+        NOTE: the ``name`` binding allows API services to override the
+        binding to use different resource name schemes, such as
+        ``users/*/operations``. To override the binding, API services
+        can add a binding such as ``"/v1/{name=users/*}/operations"`` to
+        their service configuration. For backwards compatibility, the
+        default name includes the operations collection id, however
+        overriding users must ensure the name binding is the parent
+        resource, without the operations collection id.
+
+        Args:
+            name (str):
+                The name of the operation's parent
+                resource.
+            filter_ (str):
+                The standard list filter.
+                This corresponds to the ``filter`` field
+                on the ``request`` instance; if ``request`` is provided, this
+                should not be set.
+            retry (google.api_core.retry.Retry): Designation of what errors, if any,
+                should be retried.
+            timeout (float): The timeout for this request.
+            metadata (Sequence[Tuple[str, str]]): Strings which should be
+                sent along with the request as metadata.
+
+        Returns:
+            google.api_core.operations_v1.pagers.ListOperationsPager:
+                The response message for
+                [Operations.ListOperations][google.api_core.operations_v1.Operations.ListOperations].
+
+                Iterating over this object will yield results and
+                resolve additional pages automatically.
+
+        """
+        # Create a protobuf request object.
+        request = operations_pb2.ListOperationsRequest(name=name, filter=filter_)
+        if page_size is not None:
+            request.page_size = page_size
+        if page_token is not None:
+            request.page_token = page_token
+
+        # Wrap the RPC method; this adds retry and timeout information,
+        # and friendly error handling.
+        rpc = self._transport._wrapped_methods[self._transport.list_operations]
+
+        # Certain fields should be provided within the metadata header;
+        # add these here.
+        metadata = tuple(metadata or ()) + (
+            gapic_v1.routing_header.to_grpc_metadata((("name", request.name),)),
+        )
+
+        # Send the request.
+        response = rpc(request, retry=retry, timeout=timeout, metadata=metadata,)
+
+        # This method is paged; wrap the response in a pager, which provides
+        # an `__iter__` convenience method.
+        response = pagers.ListOperationsPager(
+            method=rpc, request=request, response=response, metadata=metadata,
+        )
+
+        # Done; return the response.
+        return response
+
+    def get_operation(
+        self,
+        name: str,
+        *,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
+        timeout: Optional[float] = None,
+        metadata: Sequence[Tuple[str, str]] = (),
+    ) -> operations_pb2.Operation:
+        r"""Gets the latest state of a long-running operation.
+        Clients can use this method to poll the operation result
+        at intervals as recommended by the API service.
+
+        Args:
+            name (str):
+                The name of the operation resource.
+            retry (google.api_core.retry.Retry): Designation of what errors, if any,
+                should be retried.
+            timeout (float): The timeout for this request.
+            metadata (Sequence[Tuple[str, str]]): Strings which should be
+                sent along with the request as metadata.
+
+        Returns:
+            google.longrunning.operations_pb2.Operation:
+                This resource represents a long-
+                unning operation that is the result of a
+                network API call.
+
+        """
+
+        request = operations_pb2.GetOperationRequest(name=name)
+
+        # Wrap the RPC method; this adds retry and timeout information,
+        # and friendly error handling.
+        rpc = self._transport._wrapped_methods[self._transport.get_operation]
+
+        # Certain fields should be provided within the metadata header;
+        # add these here.
+        metadata = tuple(metadata or ()) + (
+            gapic_v1.routing_header.to_grpc_metadata((("name", request.name),)),
+        )
+
+        # Send the request.
+        response = rpc(request, retry=retry, timeout=timeout, metadata=metadata,)
+
+        # Done; return the response.
+        return response
+
+    def delete_operation(
+        self,
+        name: str,
+        *,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
+        timeout: Optional[float] = None,
+        metadata: Sequence[Tuple[str, str]] = (),
+    ) -> None:
+        r"""Deletes a long-running operation. This method indicates that the
+        client is no longer interested in the operation result. It does
+        not cancel the operation. If the server doesn't support this
+        method, it returns ``google.rpc.Code.UNIMPLEMENTED``.
+
+        Args:
+            name (str):
+                The name of the operation resource to
+                be deleted.
+
+                This corresponds to the ``name`` field
+                on the ``request`` instance; if ``request`` is provided, this
+                should not be set.
+            retry (google.api_core.retry.Retry): Designation of what errors, if any,
+                should be retried.
+            timeout (float): The timeout for this request.
+            metadata (Sequence[Tuple[str, str]]): Strings which should be
+                sent along with the request as metadata.
+        """
+        # Create the request object.
+        request = operations_pb2.DeleteOperationRequest(name=name)
+
+        # Wrap the RPC method; this adds retry and timeout information,
+        # and friendly error handling.
+        rpc = self._transport._wrapped_methods[self._transport.delete_operation]
+
+        # Certain fields should be provided within the metadata header;
+        # add these here.
+        metadata = tuple(metadata or ()) + (
+            gapic_v1.routing_header.to_grpc_metadata((("name", request.name),)),
+        )
+
+        # Send the request.
+        rpc(
+            request, retry=retry, timeout=timeout, metadata=metadata,
+        )
+
+    def cancel_operation(
+        self,
+        name: Optional[str] = None,
+        *,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
+        timeout: Optional[float] = None,
+        metadata: Sequence[Tuple[str, str]] = (),
+    ) -> None:
+        r"""Starts asynchronous cancellation on a long-running operation.
+        The server makes a best effort to cancel the operation, but
+        success is not guaranteed. If the server doesn't support this
+        method, it returns ``google.rpc.Code.UNIMPLEMENTED``. Clients
+        can use
+        [Operations.GetOperation][google.api_core.operations_v1.Operations.GetOperation]
+        or other methods to check whether the cancellation succeeded or
+        whether the operation completed despite cancellation. On
+        successful cancellation, the operation is not deleted; instead,
+        it becomes an operation with an
+        [Operation.error][google.api_core.operations_v1.Operation.error] value with
+        a [google.rpc.Status.code][google.rpc.Status.code] of 1,
+        corresponding to ``Code.CANCELLED``.
+
+        Args:
+            name (str):
+                The name of the operation resource to
+                be cancelled.
+
+                This corresponds to the ``name`` field
+                on the ``request`` instance; if ``request`` is provided, this
+                should not be set.
+            retry (google.api_core.retry.Retry): Designation of what errors, if any,
+                should be retried.
+            timeout (float): The timeout for this request.
+            metadata (Sequence[Tuple[str, str]]): Strings which should be
+                sent along with the request as metadata.
+        """
+        # Create the request object.
+        request = operations_pb2.CancelOperationRequest(name=name)
+
+        # Wrap the RPC method; this adds retry and timeout information,
+        # and friendly error handling.
+        rpc = self._transport._wrapped_methods[self._transport.cancel_operation]
+
+        # Certain fields should be provided within the metadata header;
+        # add these here.
+        metadata = tuple(metadata or ()) + (
+            gapic_v1.routing_header.to_grpc_metadata((("name", request.name),)),
+        )
+
+        # Send the request.
+        rpc(
+            request, retry=retry, timeout=timeout, metadata=metadata,
+        )
diff --git a/google/api_core/operations_v1/operations_async_client.py b/google/api_core/operations_v1/operations_async_client.py
new file mode 100644
index 0000000..5a5e556
--- /dev/null
+++ b/google/api_core/operations_v1/operations_async_client.py
@@ -0,0 +1,322 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""An async client for the google.longrunning.operations meta-API.
+
+.. _Google API Style Guide:
+    https://cloud.google.com/apis/design/design_pattern
+    s#long_running_operations
+.. _google/longrunning/operations.proto:
+    https://github.com/googleapis/googleapis/blob/master/google/longrunning
+    /operations.proto
+"""
+
+import functools
+
+from google.api_core import gapic_v1, page_iterator_async
+from google.api_core.operations_v1 import operations_client_config
+from google.longrunning import operations_pb2
+
+
+class OperationsAsyncClient:
+    """Async client for interacting with long-running operations.
+
+    Args:
+        channel (aio.Channel): The gRPC AsyncIO channel associated with the
+            service that implements the ``google.longrunning.operations``
+            interface.
+        client_config (dict):
+            A dictionary of call options for each method. If not specified
+            the default configuration is used.
+    """
+
+    def __init__(self, channel, client_config=operations_client_config.config):
+        # Create the gRPC client stub with gRPC AsyncIO channel.
+        self.operations_stub = operations_pb2.OperationsStub(channel)
+
+        # Create all wrapped methods using the interface configuration.
+        # The interface config contains all of the default settings for retry
+        # and timeout for each RPC method.
+        interfaces = client_config["interfaces"]
+        interface_config = interfaces["google.longrunning.Operations"]
+        method_configs = gapic_v1.config_async.parse_method_configs(interface_config)
+
+        self._get_operation = gapic_v1.method_async.wrap_method(
+            self.operations_stub.GetOperation,
+            default_retry=method_configs["GetOperation"].retry,
+            default_timeout=method_configs["GetOperation"].timeout,
+        )
+
+        self._list_operations = gapic_v1.method_async.wrap_method(
+            self.operations_stub.ListOperations,
+            default_retry=method_configs["ListOperations"].retry,
+            default_timeout=method_configs["ListOperations"].timeout,
+        )
+
+        self._cancel_operation = gapic_v1.method_async.wrap_method(
+            self.operations_stub.CancelOperation,
+            default_retry=method_configs["CancelOperation"].retry,
+            default_timeout=method_configs["CancelOperation"].timeout,
+        )
+
+        self._delete_operation = gapic_v1.method_async.wrap_method(
+            self.operations_stub.DeleteOperation,
+            default_retry=method_configs["DeleteOperation"].retry,
+            default_timeout=method_configs["DeleteOperation"].timeout,
+        )
+
+    async def get_operation(
+        self,
+        name,
+        retry=gapic_v1.method_async.DEFAULT,
+        timeout=gapic_v1.method_async.DEFAULT,
+        metadata=None,
+    ):
+        """Gets the latest state of a long-running operation.
+
+        Clients can use this method to poll the operation result at intervals
+        as recommended by the API service.
+
+        Example:
+            >>> from google.api_core import operations_v1
+            >>> api = operations_v1.OperationsClient()
+            >>> name = ''
+            >>> response = await api.get_operation(name)
+
+        Args:
+            name (str): The name of the operation resource.
+            retry (google.api_core.retry.Retry): The retry strategy to use
+                when invoking the RPC. If unspecified, the default retry from
+                the client configuration will be used. If ``None``, then this
+                method will not retry the RPC at all.
+            timeout (float): The amount of time in seconds to wait for the RPC
+                to complete. Note that if ``retry`` is used, this timeout
+                applies to each individual attempt and the overall time it
+                takes for this method to complete may be longer. If
+                unspecified, the the default timeout in the client
+                configuration is used. If ``None``, then the RPC method will
+                not time out.
+            metadata (Optional[List[Tuple[str, str]]]):
+                Additional gRPC metadata.
+
+        Returns:
+            google.longrunning.operations_pb2.Operation: The state of the
+                operation.
+
+        Raises:
+            google.api_core.exceptions.GoogleAPICallError: If an error occurred
+                while invoking the RPC, the appropriate ``GoogleAPICallError``
+                subclass will be raised.
+        """
+        request = operations_pb2.GetOperationRequest(name=name)
+
+        # Add routing header
+        metadata = metadata or []
+        metadata.append(gapic_v1.routing_header.to_grpc_metadata({"name": name}))
+
+        return await self._get_operation(
+            request, retry=retry, timeout=timeout, metadata=metadata
+        )
+
+    async def list_operations(
+        self,
+        name,
+        filter_,
+        retry=gapic_v1.method_async.DEFAULT,
+        timeout=gapic_v1.method_async.DEFAULT,
+        metadata=None,
+    ):
+        """
+        Lists operations that match the specified filter in the request.
+
+        Example:
+            >>> from google.api_core import operations_v1
+            >>> api = operations_v1.OperationsClient()
+            >>> name = ''
+            >>>
+            >>> # Iterate over all results
+            >>> for operation in await api.list_operations(name):
+            >>>   # process operation
+            >>>   pass
+            >>>
+            >>> # Or iterate over results one page at a time
+            >>> iter = await api.list_operations(name)
+            >>> for page in iter.pages:
+            >>>   for operation in page:
+            >>>     # process operation
+            >>>     pass
+
+        Args:
+            name (str): The name of the operation collection.
+            filter_ (str): The standard list filter.
+            retry (google.api_core.retry.Retry): The retry strategy to use
+                when invoking the RPC. If unspecified, the default retry from
+                the client configuration will be used. If ``None``, then this
+                method will not retry the RPC at all.
+            timeout (float): The amount of time in seconds to wait for the RPC
+                to complete. Note that if ``retry`` is used, this timeout
+                applies to each individual attempt and the overall time it
+                takes for this method to complete may be longer. If
+                unspecified, the the default timeout in the client
+                configuration is used. If ``None``, then the RPC method will
+                not time out.
+            metadata (Optional[List[Tuple[str, str]]]): Additional gRPC
+                metadata.
+
+        Returns:
+            google.api_core.page_iterator.Iterator: An iterator that yields
+                :class:`google.longrunning.operations_pb2.Operation` instances.
+
+        Raises:
+            google.api_core.exceptions.MethodNotImplemented: If the server
+                does not support this method. Services are not required to
+                implement this method.
+            google.api_core.exceptions.GoogleAPICallError: If an error occurred
+                while invoking the RPC, the appropriate ``GoogleAPICallError``
+                subclass will be raised.
+        """
+        # Create the request object.
+        request = operations_pb2.ListOperationsRequest(name=name, filter=filter_)
+
+        # Add routing header
+        metadata = metadata or []
+        metadata.append(gapic_v1.routing_header.to_grpc_metadata({"name": name}))
+
+        # Create the method used to fetch pages
+        method = functools.partial(
+            self._list_operations, retry=retry, timeout=timeout, metadata=metadata
+        )
+
+        iterator = page_iterator_async.AsyncGRPCIterator(
+            client=None,
+            method=method,
+            request=request,
+            items_field="operations",
+            request_token_field="page_token",
+            response_token_field="next_page_token",
+        )
+
+        return iterator
+
+    async def cancel_operation(
+        self,
+        name,
+        retry=gapic_v1.method_async.DEFAULT,
+        timeout=gapic_v1.method_async.DEFAULT,
+        metadata=None,
+    ):
+        """Starts asynchronous cancellation on a long-running operation.
+
+        The server makes a best effort to cancel the operation, but success is
+        not guaranteed. Clients can use :meth:`get_operation` or service-
+        specific methods to check whether the cancellation succeeded or whether
+        the operation completed despite cancellation. On successful
+        cancellation, the operation is not deleted; instead, it becomes an
+        operation with an ``Operation.error`` value with a
+        ``google.rpc.Status.code`` of ``1``, corresponding to
+        ``Code.CANCELLED``.
+
+        Example:
+            >>> from google.api_core import operations_v1
+            >>> api = operations_v1.OperationsClient()
+            >>> name = ''
+            >>> api.cancel_operation(name)
+
+        Args:
+            name (str): The name of the operation resource to be cancelled.
+            retry (google.api_core.retry.Retry): The retry strategy to use
+                when invoking the RPC. If unspecified, the default retry from
+                the client configuration will be used. If ``None``, then this
+                method will not retry the RPC at all.
+            timeout (float): The amount of time in seconds to wait for the RPC
+                to complete. Note that if ``retry`` is used, this timeout
+                applies to each individual attempt and the overall time it
+                takes for this method to complete may be longer. If
+                unspecified, the the default timeout in the client
+                configuration is used. If ``None``, then the RPC method will
+                not time out.
+
+        Raises:
+            google.api_core.exceptions.MethodNotImplemented: If the server
+                does not support this method. Services are not required to
+                implement this method.
+            google.api_core.exceptions.GoogleAPICallError: If an error occurred
+                while invoking the RPC, the appropriate ``GoogleAPICallError``
+                subclass will be raised.
+            metadata (Optional[List[Tuple[str, str]]]): Additional gRPC
+                metadata.
+        """
+        # Create the request object.
+        request = operations_pb2.CancelOperationRequest(name=name)
+
+        # Add routing header
+        metadata = metadata or []
+        metadata.append(gapic_v1.routing_header.to_grpc_metadata({"name": name}))
+
+        await self._cancel_operation(
+            request, retry=retry, timeout=timeout, metadata=metadata
+        )
+
+    async def delete_operation(
+        self,
+        name,
+        retry=gapic_v1.method_async.DEFAULT,
+        timeout=gapic_v1.method_async.DEFAULT,
+        metadata=None,
+    ):
+        """Deletes a long-running operation.
+
+        This method indicates that the client is no longer interested in the
+        operation result. It does not cancel the operation.
+
+        Example:
+            >>> from google.api_core import operations_v1
+            >>> api = operations_v1.OperationsClient()
+            >>> name = ''
+            >>> api.delete_operation(name)
+
+        Args:
+            name (str): The name of the operation resource to be deleted.
+            retry (google.api_core.retry.Retry): The retry strategy to use
+                when invoking the RPC. If unspecified, the default retry from
+                the client configuration will be used. If ``None``, then this
+                method will not retry the RPC at all.
+            timeout (float): The amount of time in seconds to wait for the RPC
+                to complete. Note that if ``retry`` is used, this timeout
+                applies to each individual attempt and the overall time it
+                takes for this method to complete may be longer. If
+                unspecified, the the default timeout in the client
+                configuration is used. If ``None``, then the RPC method will
+                not time out.
+            metadata (Optional[List[Tuple[str, str]]]): Additional gRPC
+                metadata.
+
+        Raises:
+            google.api_core.exceptions.MethodNotImplemented: If the server
+                does not support this method. Services are not required to
+                implement this method.
+            google.api_core.exceptions.GoogleAPICallError: If an error occurred
+                while invoking the RPC, the appropriate ``GoogleAPICallError``
+                subclass will be raised.
+        """
+        # Create the request object.
+        request = operations_pb2.DeleteOperationRequest(name=name)
+
+        # Add routing header
+        metadata = metadata or []
+        metadata.append(gapic_v1.routing_header.to_grpc_metadata({"name": name}))
+
+        await self._delete_operation(
+            request, retry=retry, timeout=timeout, metadata=metadata
+        )
diff --git a/google/api_core/operations_v1/operations_client.py b/google/api_core/operations_v1/operations_client.py
new file mode 100644
index 0000000..e48eac0
--- /dev/null
+++ b/google/api_core/operations_v1/operations_client.py
@@ -0,0 +1,332 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""A client for the google.longrunning.operations meta-API.
+
+This is a client that deals with long-running operations that follow the
+pattern outlined by the `Google API Style Guide`_.
+
+When an API method normally takes long time to complete, it can be designed to
+return ``Operation`` to the client, and the client can use this interface to
+receive the real response asynchronously by polling the operation resource to
+receive the response.
+
+It is not a separate service, but rather an interface implemented by a larger
+service. The protocol-level definition is available at
+`google/longrunning/operations.proto`_. Typically, this will be constructed
+automatically by another client class to deal with operations.
+
+.. _Google API Style Guide:
+    https://cloud.google.com/apis/design/design_pattern
+    s#long_running_operations
+.. _google/longrunning/operations.proto:
+    https://github.com/googleapis/googleapis/blob/master/google/longrunning
+    /operations.proto
+"""
+
+import functools
+
+from google.api_core import gapic_v1
+from google.api_core import page_iterator
+from google.api_core.operations_v1 import operations_client_config
+from google.longrunning import operations_pb2
+
+
+class OperationsClient(object):
+    """Client for interacting with long-running operations within a service.
+
+    Args:
+        channel (grpc.Channel): The gRPC channel associated with the service
+            that implements the ``google.longrunning.operations`` interface.
+        client_config (dict):
+            A dictionary of call options for each method. If not specified
+            the default configuration is used.
+    """
+
+    def __init__(self, channel, client_config=operations_client_config.config):
+        # Create the gRPC client stub.
+        self.operations_stub = operations_pb2.OperationsStub(channel)
+
+        # Create all wrapped methods using the interface configuration.
+        # The interface config contains all of the default settings for retry
+        # and timeout for each RPC method.
+        interfaces = client_config["interfaces"]
+        interface_config = interfaces["google.longrunning.Operations"]
+        method_configs = gapic_v1.config.parse_method_configs(interface_config)
+
+        self._get_operation = gapic_v1.method.wrap_method(
+            self.operations_stub.GetOperation,
+            default_retry=method_configs["GetOperation"].retry,
+            default_timeout=method_configs["GetOperation"].timeout,
+        )
+
+        self._list_operations = gapic_v1.method.wrap_method(
+            self.operations_stub.ListOperations,
+            default_retry=method_configs["ListOperations"].retry,
+            default_timeout=method_configs["ListOperations"].timeout,
+        )
+
+        self._cancel_operation = gapic_v1.method.wrap_method(
+            self.operations_stub.CancelOperation,
+            default_retry=method_configs["CancelOperation"].retry,
+            default_timeout=method_configs["CancelOperation"].timeout,
+        )
+
+        self._delete_operation = gapic_v1.method.wrap_method(
+            self.operations_stub.DeleteOperation,
+            default_retry=method_configs["DeleteOperation"].retry,
+            default_timeout=method_configs["DeleteOperation"].timeout,
+        )
+
+    # Service calls
+    def get_operation(
+        self,
+        name,
+        retry=gapic_v1.method.DEFAULT,
+        timeout=gapic_v1.method.DEFAULT,
+        metadata=None,
+    ):
+        """Gets the latest state of a long-running operation.
+
+        Clients can use this method to poll the operation result at intervals
+        as recommended by the API service.
+
+        Example:
+            >>> from google.api_core import operations_v1
+            >>> api = operations_v1.OperationsClient()
+            >>> name = ''
+            >>> response = api.get_operation(name)
+
+        Args:
+            name (str): The name of the operation resource.
+            retry (google.api_core.retry.Retry): The retry strategy to use
+                when invoking the RPC. If unspecified, the default retry from
+                the client configuration will be used. If ``None``, then this
+                method will not retry the RPC at all.
+            timeout (float): The amount of time in seconds to wait for the RPC
+                to complete. Note that if ``retry`` is used, this timeout
+                applies to each individual attempt and the overall time it
+                takes for this method to complete may be longer. If
+                unspecified, the the default timeout in the client
+                configuration is used. If ``None``, then the RPC method will
+                not time out.
+            metadata (Optional[List[Tuple[str, str]]]):
+                Additional gRPC metadata.
+
+        Returns:
+            google.longrunning.operations_pb2.Operation: The state of the
+                operation.
+
+        Raises:
+            google.api_core.exceptions.GoogleAPICallError: If an error occurred
+                while invoking the RPC, the appropriate ``GoogleAPICallError``
+                subclass will be raised.
+        """
+        request = operations_pb2.GetOperationRequest(name=name)
+
+        # Add routing header
+        metadata = metadata or []
+        metadata.append(gapic_v1.routing_header.to_grpc_metadata({"name": name}))
+
+        return self._get_operation(
+            request, retry=retry, timeout=timeout, metadata=metadata
+        )
+
+    def list_operations(
+        self,
+        name,
+        filter_,
+        retry=gapic_v1.method.DEFAULT,
+        timeout=gapic_v1.method.DEFAULT,
+        metadata=None,
+    ):
+        """
+        Lists operations that match the specified filter in the request.
+
+        Example:
+            >>> from google.api_core import operations_v1
+            >>> api = operations_v1.OperationsClient()
+            >>> name = ''
+            >>>
+            >>> # Iterate over all results
+            >>> for operation in api.list_operations(name):
+            >>>   # process operation
+            >>>   pass
+            >>>
+            >>> # Or iterate over results one page at a time
+            >>> iter = api.list_operations(name)
+            >>> for page in iter.pages:
+            >>>   for operation in page:
+            >>>     # process operation
+            >>>     pass
+
+        Args:
+            name (str): The name of the operation collection.
+            filter_ (str): The standard list filter.
+            retry (google.api_core.retry.Retry): The retry strategy to use
+                when invoking the RPC. If unspecified, the default retry from
+                the client configuration will be used. If ``None``, then this
+                method will not retry the RPC at all.
+            timeout (float): The amount of time in seconds to wait for the RPC
+                to complete. Note that if ``retry`` is used, this timeout
+                applies to each individual attempt and the overall time it
+                takes for this method to complete may be longer. If
+                unspecified, the the default timeout in the client
+                configuration is used. If ``None``, then the RPC method will
+                not time out.
+            metadata (Optional[List[Tuple[str, str]]]): Additional gRPC
+                metadata.
+
+        Returns:
+            google.api_core.page_iterator.Iterator: An iterator that yields
+                :class:`google.longrunning.operations_pb2.Operation` instances.
+
+        Raises:
+            google.api_core.exceptions.MethodNotImplemented: If the server
+                does not support this method. Services are not required to
+                implement this method.
+            google.api_core.exceptions.GoogleAPICallError: If an error occurred
+                while invoking the RPC, the appropriate ``GoogleAPICallError``
+                subclass will be raised.
+        """
+        # Create the request object.
+        request = operations_pb2.ListOperationsRequest(name=name, filter=filter_)
+
+        # Add routing header
+        metadata = metadata or []
+        metadata.append(gapic_v1.routing_header.to_grpc_metadata({"name": name}))
+
+        # Create the method used to fetch pages
+        method = functools.partial(
+            self._list_operations, retry=retry, timeout=timeout, metadata=metadata
+        )
+
+        iterator = page_iterator.GRPCIterator(
+            client=None,
+            method=method,
+            request=request,
+            items_field="operations",
+            request_token_field="page_token",
+            response_token_field="next_page_token",
+        )
+
+        return iterator
+
+    def cancel_operation(
+        self,
+        name,
+        retry=gapic_v1.method.DEFAULT,
+        timeout=gapic_v1.method.DEFAULT,
+        metadata=None,
+    ):
+        """Starts asynchronous cancellation on a long-running operation.
+
+        The server makes a best effort to cancel the operation, but success is
+        not guaranteed. Clients can use :meth:`get_operation` or service-
+        specific methods to check whether the cancellation succeeded or whether
+        the operation completed despite cancellation. On successful
+        cancellation, the operation is not deleted; instead, it becomes an
+        operation with an ``Operation.error`` value with a
+        ``google.rpc.Status.code`` of ``1``, corresponding to
+        ``Code.CANCELLED``.
+
+        Example:
+            >>> from google.api_core import operations_v1
+            >>> api = operations_v1.OperationsClient()
+            >>> name = ''
+            >>> api.cancel_operation(name)
+
+        Args:
+            name (str): The name of the operation resource to be cancelled.
+            retry (google.api_core.retry.Retry): The retry strategy to use
+                when invoking the RPC. If unspecified, the default retry from
+                the client configuration will be used. If ``None``, then this
+                method will not retry the RPC at all.
+            timeout (float): The amount of time in seconds to wait for the RPC
+                to complete. Note that if ``retry`` is used, this timeout
+                applies to each individual attempt and the overall time it
+                takes for this method to complete may be longer. If
+                unspecified, the the default timeout in the client
+                configuration is used. If ``None``, then the RPC method will
+                not time out.
+            metadata (Optional[List[Tuple[str, str]]]): Additional gRPC
+                metadata.
+
+        Raises:
+            google.api_core.exceptions.MethodNotImplemented: If the server
+                does not support this method. Services are not required to
+                implement this method.
+            google.api_core.exceptions.GoogleAPICallError: If an error occurred
+                while invoking the RPC, the appropriate ``GoogleAPICallError``
+                subclass will be raised.
+        """
+        # Create the request object.
+        request = operations_pb2.CancelOperationRequest(name=name)
+
+        # Add routing header
+        metadata = metadata or []
+        metadata.append(gapic_v1.routing_header.to_grpc_metadata({"name": name}))
+
+        self._cancel_operation(request, retry=retry, timeout=timeout, metadata=metadata)
+
+    def delete_operation(
+        self,
+        name,
+        retry=gapic_v1.method.DEFAULT,
+        timeout=gapic_v1.method.DEFAULT,
+        metadata=None,
+    ):
+        """Deletes a long-running operation.
+
+        This method indicates that the client is no longer interested in the
+        operation result. It does not cancel the operation.
+
+        Example:
+            >>> from google.api_core import operations_v1
+            >>> api = operations_v1.OperationsClient()
+            >>> name = ''
+            >>> api.delete_operation(name)
+
+        Args:
+            name (str): The name of the operation resource to be deleted.
+            retry (google.api_core.retry.Retry): The retry strategy to use
+                when invoking the RPC. If unspecified, the default retry from
+                the client configuration will be used. If ``None``, then this
+                method will not retry the RPC at all.
+            timeout (float): The amount of time in seconds to wait for the RPC
+                to complete. Note that if ``retry`` is used, this timeout
+                applies to each individual attempt and the overall time it
+                takes for this method to complete may be longer. If
+                unspecified, the the default timeout in the client
+                configuration is used. If ``None``, then the RPC method will
+                not time out.
+            metadata (Optional[List[Tuple[str, str]]]): Additional gRPC
+                metadata.
+
+        Raises:
+            google.api_core.exceptions.MethodNotImplemented: If the server
+                does not support this method. Services are not required to
+                implement this method.
+            google.api_core.exceptions.GoogleAPICallError: If an error occurred
+                while invoking the RPC, the appropriate ``GoogleAPICallError``
+                subclass will be raised.
+        """
+        # Create the request object.
+        request = operations_pb2.DeleteOperationRequest(name=name)
+
+        # Add routing header
+        metadata = metadata or []
+        metadata.append(gapic_v1.routing_header.to_grpc_metadata({"name": name}))
+
+        self._delete_operation(request, retry=retry, timeout=timeout, metadata=metadata)
diff --git a/google/api_core/operations_v1/operations_client_config.py b/google/api_core/operations_v1/operations_client_config.py
new file mode 100644
index 0000000..6cf9575
--- /dev/null
+++ b/google/api_core/operations_v1/operations_client_config.py
@@ -0,0 +1,59 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""gapic configuration for the googe.longrunning.operations client."""
+
+config = {
+    "interfaces": {
+        "google.longrunning.Operations": {
+            "retry_codes": {
+                "idempotent": ["DEADLINE_EXCEEDED", "UNAVAILABLE"],
+                "non_idempotent": [],
+            },
+            "retry_params": {
+                "default": {
+                    "initial_retry_delay_millis": 100,
+                    "retry_delay_multiplier": 1.3,
+                    "max_retry_delay_millis": 60000,
+                    "initial_rpc_timeout_millis": 20000,
+                    "rpc_timeout_multiplier": 1.0,
+                    "max_rpc_timeout_millis": 600000,
+                    "total_timeout_millis": 600000,
+                }
+            },
+            "methods": {
+                "GetOperation": {
+                    "timeout_millis": 60000,
+                    "retry_codes_name": "idempotent",
+                    "retry_params_name": "default",
+                },
+                "ListOperations": {
+                    "timeout_millis": 60000,
+                    "retry_codes_name": "idempotent",
+                    "retry_params_name": "default",
+                },
+                "CancelOperation": {
+                    "timeout_millis": 60000,
+                    "retry_codes_name": "idempotent",
+                    "retry_params_name": "default",
+                },
+                "DeleteOperation": {
+                    "timeout_millis": 60000,
+                    "retry_codes_name": "idempotent",
+                    "retry_params_name": "default",
+                },
+            },
+        }
+    }
+}
diff --git a/google/api_core/operations_v1/pagers.py b/google/api_core/operations_v1/pagers.py
new file mode 100644
index 0000000..b8a4775
--- /dev/null
+++ b/google/api_core/operations_v1/pagers.py
@@ -0,0 +1,86 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+from typing import (
+    Any,
+    Callable,
+    Iterator,
+    Sequence,
+    Tuple,
+)
+
+from google.longrunning import operations_pb2
+
+
+class ListOperationsPager:
+    """A pager for iterating through ``list_operations`` requests.
+
+    This class thinly wraps an initial
+    :class:`google.longrunning.operations_pb2.ListOperationsResponse` object, and
+    provides an ``__iter__`` method to iterate through its
+    ``operations`` field.
+
+    If there are more pages, the ``__iter__`` method will make additional
+    ``ListOperations`` requests and continue to iterate
+    through the ``operations`` field on the
+    corresponding responses.
+
+    All the usual :class:`google.longrunning.operations_pb2.ListOperationsResponse`
+    attributes are available on the pager. If multiple requests are made, only
+    the most recent response is retained, and thus used for attribute lookup.
+    """
+
+    def __init__(
+        self,
+        method: Callable[..., operations_pb2.ListOperationsResponse],
+        request: operations_pb2.ListOperationsRequest,
+        response: operations_pb2.ListOperationsResponse,
+        *,
+        metadata: Sequence[Tuple[str, str]] = ()
+    ):
+        """Instantiate the pager.
+
+        Args:
+            method (Callable): The method that was originally called, and
+                which instantiated this pager.
+            request (google.longrunning.operations_pb2.ListOperationsRequest):
+                The initial request object.
+            response (google.longrunning.operations_pb2.ListOperationsResponse):
+                The initial response object.
+            metadata (Sequence[Tuple[str, str]]): Strings which should be
+                sent along with the request as metadata.
+        """
+        self._method = method
+        self._request = request
+        self._response = response
+        self._metadata = metadata
+
+    def __getattr__(self, name: str) -> Any:
+        return getattr(self._response, name)
+
+    @property
+    def pages(self) -> Iterator[operations_pb2.ListOperationsResponse]:
+        yield self._response
+        while self._response.next_page_token:
+            self._request.page_token = self._response.next_page_token
+            self._response = self._method(self._request, metadata=self._metadata)
+            yield self._response
+
+    def __iter__(self) -> Iterator[operations_pb2.Operation]:
+        for page in self.pages:
+            yield from page.operations
+
+    def __repr__(self) -> str:
+        return "{0}<{1!r}>".format(self.__class__.__name__, self._response)
diff --git a/google/api_core/operations_v1/transports/__init__.py b/google/api_core/operations_v1/transports/__init__.py
new file mode 100644
index 0000000..b443c07
--- /dev/null
+++ b/google/api_core/operations_v1/transports/__init__.py
@@ -0,0 +1,30 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+from collections import OrderedDict
+from typing import Dict, Type
+
+from .base import OperationsTransport
+from .rest import OperationsRestTransport
+
+
+# Compile a registry of transports.
+_transport_registry = OrderedDict()  # type: Dict[str, Type[OperationsTransport]]
+_transport_registry["rest"] = OperationsRestTransport
+
+__all__ = (
+    "OperationsTransport",
+    "OperationsRestTransport",
+)
diff --git a/google/api_core/operations_v1/transports/base.py b/google/api_core/operations_v1/transports/base.py
new file mode 100644
index 0000000..460e646
--- /dev/null
+++ b/google/api_core/operations_v1/transports/base.py
@@ -0,0 +1,232 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+import abc
+from typing import Awaitable, Callable, Optional, Sequence, Union
+
+import pkg_resources
+
+import google.api_core  # type: ignore
+from google.api_core import exceptions as core_exceptions  # type: ignore
+from google.api_core import gapic_v1  # type: ignore
+from google.api_core import retry as retries  # type: ignore
+import google.auth  # type: ignore
+from google.auth import credentials as ga_credentials  # type: ignore
+from google.longrunning import operations_pb2
+from google.oauth2 import service_account  # type: ignore
+from google.protobuf import empty_pb2  # type: ignore
+
+try:
+    DEFAULT_CLIENT_INFO = gapic_v1.client_info.ClientInfo(
+        gapic_version=pkg_resources.get_distribution(
+            "google.api_core.operations_v1",
+        ).version,
+    )
+except pkg_resources.DistributionNotFound:
+    DEFAULT_CLIENT_INFO = gapic_v1.client_info.ClientInfo()
+
+
+class OperationsTransport(abc.ABC):
+    """Abstract transport class for Operations."""
+
+    AUTH_SCOPES = ()
+
+    DEFAULT_HOST: str = "longrunning.googleapis.com"
+
+    def __init__(
+        self,
+        *,
+        host: str = DEFAULT_HOST,
+        credentials: ga_credentials.Credentials = None,
+        credentials_file: Optional[str] = None,
+        scopes: Optional[Sequence[str]] = None,
+        quota_project_id: Optional[str] = None,
+        client_info: gapic_v1.client_info.ClientInfo = DEFAULT_CLIENT_INFO,
+        always_use_jwt_access: Optional[bool] = False,
+        **kwargs,
+    ) -> None:
+        """Instantiate the transport.
+
+        Args:
+            host (Optional[str]):
+                 The hostname to connect to.
+            credentials (Optional[google.auth.credentials.Credentials]): The
+                authorization credentials to attach to requests. These
+                credentials identify the application to the service; if none
+                are specified, the client will attempt to ascertain the
+                credentials from the environment.
+            credentials_file (Optional[str]): A file with credentials that can
+                be loaded with :func:`google.auth.load_credentials_from_file`.
+                This argument is mutually exclusive with credentials.
+            scopes (Optional[Sequence[str]]): A list of scopes.
+            quota_project_id (Optional[str]): An optional project to use for billing
+                and quota.
+            client_info (google.api_core.gapic_v1.client_info.ClientInfo):
+                The client info used to send a user-agent string along with
+                API requests. If ``None``, then default info will be used.
+                Generally, you only need to set this if you're developing
+                your own client library.
+            always_use_jwt_access (Optional[bool]): Whether self signed JWT should
+                be used for service account credentials.
+        """
+        # Save the hostname. Default to port 443 (HTTPS) if none is specified.
+        if ":" not in host:
+            host += ":443"
+        self._host = host
+
+        scopes_kwargs = {"scopes": scopes, "default_scopes": self.AUTH_SCOPES}
+
+        # Save the scopes.
+        self._scopes = scopes
+
+        # If no credentials are provided, then determine the appropriate
+        # defaults.
+        if credentials and credentials_file:
+            raise core_exceptions.DuplicateCredentialArgs(
+                "'credentials_file' and 'credentials' are mutually exclusive"
+            )
+
+        if credentials_file is not None:
+            credentials, _ = google.auth.load_credentials_from_file(
+                credentials_file, **scopes_kwargs, quota_project_id=quota_project_id
+            )
+
+        elif credentials is None:
+            credentials, _ = google.auth.default(
+                **scopes_kwargs, quota_project_id=quota_project_id
+            )
+
+        # If the credentials are service account credentials, then always try to use self signed JWT.
+        if (
+            always_use_jwt_access
+            and isinstance(credentials, service_account.Credentials)
+            and hasattr(service_account.Credentials, "with_always_use_jwt_access")
+        ):
+            credentials = credentials.with_always_use_jwt_access(True)
+
+        # Save the credentials.
+        self._credentials = credentials
+
+    def _prep_wrapped_messages(self, client_info):
+        # Precompute the wrapped methods.
+        self._wrapped_methods = {
+            self.list_operations: gapic_v1.method.wrap_method(
+                self.list_operations,
+                default_retry=retries.Retry(
+                    initial=0.5,
+                    maximum=10.0,
+                    multiplier=2.0,
+                    predicate=retries.if_exception_type(
+                        core_exceptions.ServiceUnavailable,
+                    ),
+                    deadline=10.0,
+                ),
+                default_timeout=10.0,
+                client_info=client_info,
+            ),
+            self.get_operation: gapic_v1.method.wrap_method(
+                self.get_operation,
+                default_retry=retries.Retry(
+                    initial=0.5,
+                    maximum=10.0,
+                    multiplier=2.0,
+                    predicate=retries.if_exception_type(
+                        core_exceptions.ServiceUnavailable,
+                    ),
+                    deadline=10.0,
+                ),
+                default_timeout=10.0,
+                client_info=client_info,
+            ),
+            self.delete_operation: gapic_v1.method.wrap_method(
+                self.delete_operation,
+                default_retry=retries.Retry(
+                    initial=0.5,
+                    maximum=10.0,
+                    multiplier=2.0,
+                    predicate=retries.if_exception_type(
+                        core_exceptions.ServiceUnavailable,
+                    ),
+                    deadline=10.0,
+                ),
+                default_timeout=10.0,
+                client_info=client_info,
+            ),
+            self.cancel_operation: gapic_v1.method.wrap_method(
+                self.cancel_operation,
+                default_retry=retries.Retry(
+                    initial=0.5,
+                    maximum=10.0,
+                    multiplier=2.0,
+                    predicate=retries.if_exception_type(
+                        core_exceptions.ServiceUnavailable,
+                    ),
+                    deadline=10.0,
+                ),
+                default_timeout=10.0,
+                client_info=client_info,
+            ),
+        }
+
+    def close(self):
+        """Closes resources associated with the transport.
+
+       .. warning::
+            Only call this method if the transport is NOT shared
+            with other clients - this may cause errors in other clients!
+        """
+        raise NotImplementedError()
+
+    @property
+    def list_operations(
+        self,
+    ) -> Callable[
+        [operations_pb2.ListOperationsRequest],
+        Union[
+            operations_pb2.ListOperationsResponse,
+            Awaitable[operations_pb2.ListOperationsResponse],
+        ],
+    ]:
+        raise NotImplementedError()
+
+    @property
+    def get_operation(
+        self,
+    ) -> Callable[
+        [operations_pb2.GetOperationRequest],
+        Union[operations_pb2.Operation, Awaitable[operations_pb2.Operation]],
+    ]:
+        raise NotImplementedError()
+
+    @property
+    def delete_operation(
+        self,
+    ) -> Callable[
+        [operations_pb2.DeleteOperationRequest],
+        Union[empty_pb2.Empty, Awaitable[empty_pb2.Empty]],
+    ]:
+        raise NotImplementedError()
+
+    @property
+    def cancel_operation(
+        self,
+    ) -> Callable[
+        [operations_pb2.CancelOperationRequest],
+        Union[empty_pb2.Empty, Awaitable[empty_pb2.Empty]],
+    ]:
+        raise NotImplementedError()
+
+
+__all__ = ("OperationsTransport",)
diff --git a/google/api_core/operations_v1/transports/rest.py b/google/api_core/operations_v1/transports/rest.py
new file mode 100644
index 0000000..27ed766
--- /dev/null
+++ b/google/api_core/operations_v1/transports/rest.py
@@ -0,0 +1,455 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+from typing import Callable, Dict, Optional, Sequence, Tuple, Union
+
+from requests import __version__ as requests_version
+
+from google.api_core import exceptions as core_exceptions  # type: ignore
+from google.api_core import gapic_v1  # type: ignore
+from google.api_core import path_template  # type: ignore
+from google.api_core import rest_helpers  # type: ignore
+from google.api_core import retry as retries  # type: ignore
+from google.auth import credentials as ga_credentials  # type: ignore
+from google.auth.transport.requests import AuthorizedSession  # type: ignore
+from google.longrunning import operations_pb2  # type: ignore
+from google.protobuf import empty_pb2  # type: ignore
+from google.protobuf import json_format  # type: ignore
+from .base import DEFAULT_CLIENT_INFO as BASE_DEFAULT_CLIENT_INFO, OperationsTransport
+
+OptionalRetry = Union[retries.Retry, object]
+
+DEFAULT_CLIENT_INFO = gapic_v1.client_info.ClientInfo(
+    gapic_version=BASE_DEFAULT_CLIENT_INFO.gapic_version,
+    grpc_version=None,
+    rest_version=requests_version,
+)
+
+
+class OperationsRestTransport(OperationsTransport):
+    """REST backend transport for Operations.
+
+    Manages long-running operations with an API service.
+
+    When an API method normally takes long time to complete, it can be
+    designed to return [Operation][google.api_core.operations_v1.Operation] to the
+    client, and the client can use this interface to receive the real
+    response asynchronously by polling the operation resource, or pass
+    the operation resource to another API (such as Google Cloud Pub/Sub
+    API) to receive the response. Any API service that returns
+    long-running operations should implement the ``Operations``
+    interface so developers can have a consistent client experience.
+
+    This class defines the same methods as the primary client, so the
+    primary client can load the underlying transport implementation
+    and call it.
+
+    It sends JSON representations of protocol buffers over HTTP/1.1
+    """
+
+    def __init__(
+        self,
+        *,
+        host: str = "longrunning.googleapis.com",
+        credentials: ga_credentials.Credentials = None,
+        credentials_file: Optional[str] = None,
+        scopes: Optional[Sequence[str]] = None,
+        client_cert_source_for_mtls: Optional[Callable[[], Tuple[bytes, bytes]]] = None,
+        quota_project_id: Optional[str] = None,
+        client_info: gapic_v1.client_info.ClientInfo = DEFAULT_CLIENT_INFO,
+        always_use_jwt_access: Optional[bool] = False,
+        url_scheme: str = "https",
+        http_options: Optional[Dict] = None,
+    ) -> None:
+        """Instantiate the transport.
+
+        Args:
+            host (Optional[str]):
+                 The hostname to connect to.
+            credentials (Optional[google.auth.credentials.Credentials]): The
+                authorization credentials to attach to requests. These
+                credentials identify the application to the service; if none
+                are specified, the client will attempt to ascertain the
+                credentials from the environment.
+
+            credentials_file (Optional[str]): A file with credentials that can
+                be loaded with :func:`google.auth.load_credentials_from_file`.
+                This argument is ignored if ``channel`` is provided.
+            scopes (Optional(Sequence[str])): A list of scopes. This argument is
+                ignored if ``channel`` is provided.
+            client_cert_source_for_mtls (Callable[[], Tuple[bytes, bytes]]): Client
+                certificate to configure mutual TLS HTTP channel. It is ignored
+                if ``channel`` is provided.
+            quota_project_id (Optional[str]): An optional project to use for billing
+                and quota.
+            client_info (google.api_core.gapic_v1.client_info.ClientInfo):
+                The client info used to send a user-agent string along with
+                API requests. If ``None``, then default info will be used.
+                Generally, you only need to set this if you're developing
+                your own client library.
+            always_use_jwt_access (Optional[bool]): Whether self signed JWT should
+                be used for service account credentials.
+            url_scheme: the protocol scheme for the API endpoint.  Normally
+                "https", but for testing or local servers,
+                "http" can be specified.
+            http_options: a dictionary of http_options for transcoding, to override
+                the defaults from operatons.proto.  Each method has an entry
+                with the corresponding http rules as value.
+
+        """
+        # Run the base constructor
+        # TODO(yon-mg): resolve other ctor params i.e. scopes, quota, etc.
+        # TODO: When custom host (api_endpoint) is set, `scopes` must *also* be set on the
+        # credentials object
+        super().__init__(
+            host=host,
+            credentials=credentials,
+            client_info=client_info,
+            always_use_jwt_access=always_use_jwt_access,
+        )
+        self._session = AuthorizedSession(
+            self._credentials, default_host=self.DEFAULT_HOST
+        )
+        if client_cert_source_for_mtls:
+            self._session.configure_mtls_channel(client_cert_source_for_mtls)
+        self._prep_wrapped_messages(client_info)
+        self._http_options = http_options or {}
+
+    def _list_operations(
+        self,
+        request: operations_pb2.ListOperationsRequest,
+        *,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
+        timeout: Optional[float] = None,
+        metadata: Sequence[Tuple[str, str]] = (),
+    ) -> operations_pb2.ListOperationsResponse:
+        r"""Call the list operations method over HTTP.
+
+        Args:
+            request (~.operations_pb2.ListOperationsRequest):
+                The request object. The request message for
+                [Operations.ListOperations][google.api_core.operations_v1.Operations.ListOperations].
+
+            retry (google.api_core.retry.Retry): Designation of what errors, if any,
+                should be retried.
+            timeout (float): The timeout for this request.
+            metadata (Sequence[Tuple[str, str]]): Strings which should be
+                sent along with the request as metadata.
+
+        Returns:
+            ~.operations_pb2.ListOperationsResponse:
+                The response message for
+                [Operations.ListOperations][google.api_core.operations_v1.Operations.ListOperations].
+
+        """
+
+        http_options = [
+            {"method": "get", "uri": "/v1/{name=operations}"},
+        ]
+        if "google.longrunning.Operations.ListOperations" in self._http_options:
+            http_options = self._http_options[
+                "google.longrunning.Operations.ListOperations"
+            ]
+
+        request_kwargs = json_format.MessageToDict(
+            request,
+            preserving_proto_field_name=True,
+            including_default_value_fields=True,
+        )
+        transcoded_request = path_template.transcode(http_options, **request_kwargs)
+
+        uri = transcoded_request["uri"]
+        method = transcoded_request["method"]
+
+        # Jsonify the query params
+        query_params_request = operations_pb2.ListOperationsRequest()
+        json_format.ParseDict(transcoded_request["query_params"], query_params_request)
+        query_params = json_format.MessageToDict(
+            query_params_request,
+            including_default_value_fields=False,
+            preserving_proto_field_name=False,
+            use_integers_for_enums=False,
+        )
+
+        # Send the request
+        headers = dict(metadata)
+        headers["Content-Type"] = "application/json"
+        response = getattr(self._session, method)(
+            "https://{host}{uri}".format(host=self._host, uri=uri),
+            timeout=timeout,
+            headers=headers,
+            params=rest_helpers.flatten_query_params(query_params),
+        )
+
+        # In case of error, raise the appropriate core_exceptions.GoogleAPICallError exception
+        # subclass.
+        if response.status_code >= 400:
+            raise core_exceptions.from_http_response(response)
+
+        # Return the response
+        api_response = operations_pb2.ListOperationsResponse()
+        json_format.Parse(response.content, api_response, ignore_unknown_fields=False)
+        return api_response
+
+    def _get_operation(
+        self,
+        request: operations_pb2.GetOperationRequest,
+        *,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
+        timeout: Optional[float] = None,
+        metadata: Sequence[Tuple[str, str]] = (),
+    ) -> operations_pb2.Operation:
+        r"""Call the get operation method over HTTP.
+
+        Args:
+            request (~.operations_pb2.GetOperationRequest):
+                The request object. The request message for
+                [Operations.GetOperation][google.api_core.operations_v1.Operations.GetOperation].
+
+            retry (google.api_core.retry.Retry): Designation of what errors, if any,
+                should be retried.
+            timeout (float): The timeout for this request.
+            metadata (Sequence[Tuple[str, str]]): Strings which should be
+                sent along with the request as metadata.
+
+        Returns:
+            ~.operations_pb2.Operation:
+                This resource represents a long-
+                unning operation that is the result of a
+                network API call.
+
+        """
+
+        http_options = [
+            {"method": "get", "uri": "/v1/{name=operations/**}"},
+        ]
+        if "google.longrunning.Operations.GetOperation" in self._http_options:
+            http_options = self._http_options[
+                "google.longrunning.Operations.GetOperation"
+            ]
+
+        request_kwargs = json_format.MessageToDict(
+            request,
+            preserving_proto_field_name=True,
+            including_default_value_fields=True,
+        )
+        transcoded_request = path_template.transcode(http_options, **request_kwargs)
+
+        uri = transcoded_request["uri"]
+        method = transcoded_request["method"]
+
+        # Jsonify the query params
+        query_params_request = operations_pb2.GetOperationRequest()
+        json_format.ParseDict(transcoded_request["query_params"], query_params_request)
+        query_params = json_format.MessageToDict(
+            query_params_request,
+            including_default_value_fields=False,
+            preserving_proto_field_name=False,
+            use_integers_for_enums=False,
+        )
+
+        # Send the request
+        headers = dict(metadata)
+        headers["Content-Type"] = "application/json"
+        response = getattr(self._session, method)(
+            "https://{host}{uri}".format(host=self._host, uri=uri),
+            timeout=timeout,
+            headers=headers,
+            params=rest_helpers.flatten_query_params(query_params),
+        )
+
+        # In case of error, raise the appropriate core_exceptions.GoogleAPICallError exception
+        # subclass.
+        if response.status_code >= 400:
+            raise core_exceptions.from_http_response(response)
+
+        # Return the response
+        api_response = operations_pb2.Operation()
+        json_format.Parse(response.content, api_response, ignore_unknown_fields=False)
+        return api_response
+
+    def _delete_operation(
+        self,
+        request: operations_pb2.DeleteOperationRequest,
+        *,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
+        timeout: Optional[float] = None,
+        metadata: Sequence[Tuple[str, str]] = (),
+    ) -> empty_pb2.Empty:
+        r"""Call the delete operation method over HTTP.
+
+        Args:
+            request (~.operations_pb2.DeleteOperationRequest):
+                The request object. The request message for
+                [Operations.DeleteOperation][google.api_core.operations_v1.Operations.DeleteOperation].
+
+            retry (google.api_core.retry.Retry): Designation of what errors, if any,
+                should be retried.
+            timeout (float): The timeout for this request.
+            metadata (Sequence[Tuple[str, str]]): Strings which should be
+                sent along with the request as metadata.
+        """
+
+        http_options = [
+            {"method": "delete", "uri": "/v1/{name=operations/**}"},
+        ]
+        if "google.longrunning.Operations.DeleteOperation" in self._http_options:
+            http_options = self._http_options[
+                "google.longrunning.Operations.DeleteOperation"
+            ]
+
+        request_kwargs = json_format.MessageToDict(
+            request,
+            preserving_proto_field_name=True,
+            including_default_value_fields=True,
+        )
+        transcoded_request = path_template.transcode(http_options, **request_kwargs)
+
+        uri = transcoded_request["uri"]
+        method = transcoded_request["method"]
+
+        # Jsonify the query params
+        query_params_request = operations_pb2.DeleteOperationRequest()
+        json_format.ParseDict(transcoded_request["query_params"], query_params_request)
+        query_params = json_format.MessageToDict(
+            query_params_request,
+            including_default_value_fields=False,
+            preserving_proto_field_name=False,
+            use_integers_for_enums=False,
+        )
+
+        # Send the request
+        headers = dict(metadata)
+        headers["Content-Type"] = "application/json"
+        response = getattr(self._session, method)(
+            "https://{host}{uri}".format(host=self._host, uri=uri),
+            timeout=timeout,
+            headers=headers,
+            params=rest_helpers.flatten_query_params(query_params),
+        )
+
+        # In case of error, raise the appropriate core_exceptions.GoogleAPICallError exception
+        # subclass.
+        if response.status_code >= 400:
+            raise core_exceptions.from_http_response(response)
+
+        return empty_pb2.Empty()
+
+    def _cancel_operation(
+        self,
+        request: operations_pb2.CancelOperationRequest,
+        *,
+        retry: OptionalRetry = gapic_v1.method.DEFAULT,
+        timeout: Optional[float] = None,
+        metadata: Sequence[Tuple[str, str]] = (),
+    ) -> empty_pb2.Empty:
+        r"""Call the cancel operation method over HTTP.
+
+        Args:
+            request (~.operations_pb2.CancelOperationRequest):
+                The request object. The request message for
+                [Operations.CancelOperation][google.api_core.operations_v1.Operations.CancelOperation].
+
+            retry (google.api_core.retry.Retry): Designation of what errors, if any,
+                should be retried.
+            timeout (float): The timeout for this request.
+            metadata (Sequence[Tuple[str, str]]): Strings which should be
+                sent along with the request as metadata.
+        """
+
+        http_options = [
+            {"method": "post", "uri": "/v1/{name=operations/**}:cancel", "body": "*"},
+        ]
+        if "google.longrunning.Operations.CancelOperation" in self._http_options:
+            http_options = self._http_options[
+                "google.longrunning.Operations.CancelOperation"
+            ]
+
+        request_kwargs = json_format.MessageToDict(
+            request,
+            preserving_proto_field_name=True,
+            including_default_value_fields=True,
+        )
+        transcoded_request = path_template.transcode(http_options, **request_kwargs)
+
+        # Jsonify the request body
+        body_request = operations_pb2.CancelOperationRequest()
+        json_format.ParseDict(transcoded_request["body"], body_request)
+        body = json_format.MessageToDict(
+            body_request,
+            including_default_value_fields=False,
+            preserving_proto_field_name=False,
+            use_integers_for_enums=False,
+        )
+        uri = transcoded_request["uri"]
+        method = transcoded_request["method"]
+
+        # Jsonify the query params
+        query_params_request = operations_pb2.CancelOperationRequest()
+        json_format.ParseDict(transcoded_request["query_params"], query_params_request)
+        query_params = json_format.MessageToDict(
+            query_params_request,
+            including_default_value_fields=False,
+            preserving_proto_field_name=False,
+            use_integers_for_enums=False,
+        )
+
+        # Send the request
+        headers = dict(metadata)
+        headers["Content-Type"] = "application/json"
+        response = getattr(self._session, method)(
+            "https://{host}{uri}".format(host=self._host, uri=uri),
+            timeout=timeout,
+            headers=headers,
+            params=rest_helpers.flatten_query_params(query_params),
+            data=body,
+        )
+
+        # In case of error, raise the appropriate core_exceptions.GoogleAPICallError exception
+        # subclass.
+        if response.status_code >= 400:
+            raise core_exceptions.from_http_response(response)
+
+        return empty_pb2.Empty()
+
+    @property
+    def list_operations(
+        self,
+    ) -> Callable[
+        [operations_pb2.ListOperationsRequest], operations_pb2.ListOperationsResponse
+    ]:
+        return self._list_operations
+
+    @property
+    def get_operation(
+        self,
+    ) -> Callable[[operations_pb2.GetOperationRequest], operations_pb2.Operation]:
+        return self._get_operation
+
+    @property
+    def delete_operation(
+        self,
+    ) -> Callable[[operations_pb2.DeleteOperationRequest], empty_pb2.Empty]:
+        return self._delete_operation
+
+    @property
+    def cancel_operation(
+        self,
+    ) -> Callable[[operations_pb2.CancelOperationRequest], empty_pb2.Empty]:
+        return self._cancel_operation
+
+
+__all__ = ("OperationsRestTransport",)
diff --git a/google/api_core/page_iterator.py b/google/api_core/page_iterator.py
new file mode 100644
index 0000000..7ddc5cb
--- /dev/null
+++ b/google/api_core/page_iterator.py
@@ -0,0 +1,571 @@
+# Copyright 2015 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Iterators for paging through paged API methods.
+
+These iterators simplify the process of paging through API responses
+where the request takes a page token and the response is a list of results with
+a token for the next page. See `list pagination`_ in the Google API Style Guide
+for more details.
+
+.. _list pagination:
+    https://cloud.google.com/apis/design/design_patterns#list_pagination
+
+API clients that have methods that follow the list pagination pattern can
+return an :class:`.Iterator`. You can use this iterator to get **all** of
+the results across all pages::
+
+    >>> results_iterator = client.list_resources()
+    >>> list(results_iterator)  # Convert to a list (consumes all values).
+
+Or you can walk your way through items and call off the search early if
+you find what you're looking for (resulting in possibly fewer requests)::
+
+    >>> for resource in results_iterator:
+    ...     print(resource.name)
+    ...     if not resource.is_valid:
+    ...         break
+
+At any point, you may check the number of items consumed by referencing the
+``num_results`` property of the iterator::
+
+    >>> for my_item in results_iterator:
+    ...     if results_iterator.num_results >= 10:
+    ...         break
+
+When iterating, not every new item will send a request to the server.
+To iterate based on each page of items (where a page corresponds to
+a request)::
+
+    >>> for page in results_iterator.pages:
+    ...     print('=' * 20)
+    ...     print('    Page number: {:d}'.format(iterator.page_number))
+    ...     print('  Items in page: {:d}'.format(page.num_items))
+    ...     print('     First item: {!r}'.format(next(page)))
+    ...     print('Items remaining: {:d}'.format(page.remaining))
+    ...     print('Next page token: {}'.format(iterator.next_page_token))
+    ====================
+        Page number: 1
+      Items in page: 1
+         First item: <MyItemClass at 0x7f1d3cccf690>
+    Items remaining: 0
+    Next page token: eav1OzQB0OM8rLdGXOEsyQWSG
+    ====================
+        Page number: 2
+      Items in page: 19
+         First item: <MyItemClass at 0x7f1d3cccffd0>
+    Items remaining: 18
+    Next page token: None
+
+Then, for each page you can get all the resources on that page by iterating
+through it or using :func:`list`::
+
+    >>> list(page)
+    [
+        <MyItemClass at 0x7fd64a098ad0>,
+        <MyItemClass at 0x7fd64a098ed0>,
+        <MyItemClass at 0x7fd64a098e90>,
+    ]
+"""
+
+import abc
+
+
+class Page(object):
+    """Single page of results in an iterator.
+
+    Args:
+        parent (google.api_core.page_iterator.Iterator): The iterator that owns
+            the current page.
+        items (Sequence[Any]): An iterable (that also defines __len__) of items
+            from a raw API response.
+        item_to_value (Callable[google.api_core.page_iterator.Iterator, Any]):
+            Callable to convert an item from the type in the raw API response
+            into the native object. Will be called with the iterator and a
+            single item.
+        raw_page Optional[google.protobuf.message.Message]:
+            The raw page response.
+    """
+
+    def __init__(self, parent, items, item_to_value, raw_page=None):
+        self._parent = parent
+        self._num_items = len(items)
+        self._remaining = self._num_items
+        self._item_iter = iter(items)
+        self._item_to_value = item_to_value
+        self._raw_page = raw_page
+
+    @property
+    def raw_page(self):
+        """google.protobuf.message.Message"""
+        return self._raw_page
+
+    @property
+    def num_items(self):
+        """int: Total items in the page."""
+        return self._num_items
+
+    @property
+    def remaining(self):
+        """int: Remaining items in the page."""
+        return self._remaining
+
+    def __iter__(self):
+        """The :class:`Page` is an iterator of items."""
+        return self
+
+    def __next__(self):
+        """Get the next value in the page."""
+        item = next(self._item_iter)
+        result = self._item_to_value(self._parent, item)
+        # Since we've successfully got the next value from the
+        # iterator, we update the number of remaining.
+        self._remaining -= 1
+        return result
+
+
+def _item_to_value_identity(iterator, item):
+    """An item to value transformer that returns the item un-changed."""
+    # pylint: disable=unused-argument
+    # We are conforming to the interface defined by Iterator.
+    return item
+
+
+class Iterator(object, metaclass=abc.ABCMeta):
+    """A generic class for iterating through API list responses.
+
+    Args:
+        client(google.cloud.client.Client): The API client.
+        item_to_value (Callable[google.api_core.page_iterator.Iterator, Any]):
+            Callable to convert an item from the type in the raw API response
+            into the native object. Will be called with the iterator and a
+            single item.
+        page_token (str): A token identifying a page in a result set to start
+            fetching results from.
+        max_results (int): The maximum number of results to fetch.
+    """
+
+    def __init__(
+        self,
+        client,
+        item_to_value=_item_to_value_identity,
+        page_token=None,
+        max_results=None,
+    ):
+        self._started = False
+        self.__active_iterator = None
+
+        self.client = client
+        """Optional[Any]: The client that created this iterator."""
+        self.item_to_value = item_to_value
+        """Callable[Iterator, Any]: Callable to convert an item from the type
+            in the raw API response into the native object. Will be called with
+            the iterator and a
+            single item.
+        """
+        self.max_results = max_results
+        """int: The maximum number of results to fetch"""
+
+        # The attributes below will change over the life of the iterator.
+        self.page_number = 0
+        """int: The current page of results."""
+        self.next_page_token = page_token
+        """str: The token for the next page of results. If this is set before
+            the iterator starts, it effectively offsets the iterator to a
+            specific starting point."""
+        self.num_results = 0
+        """int: The total number of results fetched so far."""
+
+    @property
+    def pages(self):
+        """Iterator of pages in the response.
+
+        returns:
+            types.GeneratorType[google.api_core.page_iterator.Page]: A
+                generator of page instances.
+
+        raises:
+            ValueError: If the iterator has already been started.
+        """
+        if self._started:
+            raise ValueError("Iterator has already started", self)
+        self._started = True
+        return self._page_iter(increment=True)
+
+    def _items_iter(self):
+        """Iterator for each item returned."""
+        for page in self._page_iter(increment=False):
+            for item in page:
+                self.num_results += 1
+                yield item
+
+    def __iter__(self):
+        """Iterator for each item returned.
+
+        Returns:
+            types.GeneratorType[Any]: A generator of items from the API.
+
+        Raises:
+            ValueError: If the iterator has already been started.
+        """
+        if self._started:
+            raise ValueError("Iterator has already started", self)
+        self._started = True
+        return self._items_iter()
+
+    def __next__(self):
+        if self.__active_iterator is None:
+            self.__active_iterator = iter(self)
+        return next(self.__active_iterator)
+
+    def _page_iter(self, increment):
+        """Generator of pages of API responses.
+
+        Args:
+            increment (bool): Flag indicating if the total number of results
+                should be incremented on each page. This is useful since a page
+                iterator will want to increment by results per page while an
+                items iterator will want to increment per item.
+
+        Yields:
+            Page: each page of items from the API.
+        """
+        page = self._next_page()
+        while page is not None:
+            self.page_number += 1
+            if increment:
+                self.num_results += page.num_items
+            yield page
+            page = self._next_page()
+
+    @abc.abstractmethod
+    def _next_page(self):
+        """Get the next page in the iterator.
+
+        This does nothing and is intended to be over-ridden by subclasses
+        to return the next :class:`Page`.
+
+        Raises:
+            NotImplementedError: Always, this method is abstract.
+        """
+        raise NotImplementedError
+
+
+def _do_nothing_page_start(iterator, page, response):
+    """Helper to provide custom behavior after a :class:`Page` is started.
+
+    This is a do-nothing stand-in as the default value.
+
+    Args:
+        iterator (Iterator): An iterator that holds some request info.
+        page (Page): The page that was just created.
+        response (Any): The API response for a page.
+    """
+    # pylint: disable=unused-argument
+    pass
+
+
+class HTTPIterator(Iterator):
+    """A generic class for iterating through HTTP/JSON API list responses.
+
+    To make an iterator work, you'll need to provide a way to convert a JSON
+    item returned from the API into the object of your choice (via
+    ``item_to_value``). You also may need to specify a custom ``items_key`` so
+    that a given response (containing a page of results) can be parsed into an
+    iterable page of the actual objects you want.
+
+    Args:
+        client (google.cloud.client.Client): The API client.
+        api_request (Callable): The function to use to make API requests.
+            Generally, this will be
+            :meth:`google.cloud._http.JSONConnection.api_request`.
+        path (str): The method path to query for the list of items.
+        item_to_value (Callable[google.api_core.page_iterator.Iterator, Any]):
+            Callable to convert an item from the type in the JSON response into
+            a native object. Will be called with the iterator and a single
+            item.
+        items_key (str): The key in the API response where the list of items
+            can be found.
+        page_token (str): A token identifying a page in a result set to start
+            fetching results from.
+        page_size (int): The maximum number of results to fetch per page
+        max_results (int): The maximum number of results to fetch
+        extra_params (dict): Extra query string parameters for the
+            API call.
+        page_start (Callable[
+            google.api_core.page_iterator.Iterator,
+            google.api_core.page_iterator.Page, dict]): Callable to provide
+            any special behavior after a new page has been created. Assumed
+            signature takes the :class:`.Iterator` that started the page,
+            the :class:`.Page` that was started and the dictionary containing
+            the page response.
+        next_token (str): The name of the field used in the response for page
+            tokens.
+
+    .. autoattribute:: pages
+    """
+
+    _DEFAULT_ITEMS_KEY = "items"
+    _PAGE_TOKEN = "pageToken"
+    _MAX_RESULTS = "maxResults"
+    _NEXT_TOKEN = "nextPageToken"
+    _RESERVED_PARAMS = frozenset([_PAGE_TOKEN])
+    _HTTP_METHOD = "GET"
+
+    def __init__(
+        self,
+        client,
+        api_request,
+        path,
+        item_to_value,
+        items_key=_DEFAULT_ITEMS_KEY,
+        page_token=None,
+        page_size=None,
+        max_results=None,
+        extra_params=None,
+        page_start=_do_nothing_page_start,
+        next_token=_NEXT_TOKEN,
+    ):
+        super(HTTPIterator, self).__init__(
+            client, item_to_value, page_token=page_token, max_results=max_results
+        )
+        self.api_request = api_request
+        self.path = path
+        self._items_key = items_key
+        self.extra_params = extra_params
+        self._page_size = page_size
+        self._page_start = page_start
+        self._next_token = next_token
+        # Verify inputs / provide defaults.
+        if self.extra_params is None:
+            self.extra_params = {}
+        self._verify_params()
+
+    def _verify_params(self):
+        """Verifies the parameters don't use any reserved parameter.
+
+        Raises:
+            ValueError: If a reserved parameter is used.
+        """
+        reserved_in_use = self._RESERVED_PARAMS.intersection(self.extra_params)
+        if reserved_in_use:
+            raise ValueError("Using a reserved parameter", reserved_in_use)
+
+    def _next_page(self):
+        """Get the next page in the iterator.
+
+        Returns:
+            Optional[Page]: The next page in the iterator or :data:`None` if
+                there are no pages left.
+        """
+        if self._has_next_page():
+            response = self._get_next_page_response()
+            items = response.get(self._items_key, ())
+            page = Page(self, items, self.item_to_value, raw_page=response)
+            self._page_start(self, page, response)
+            self.next_page_token = response.get(self._next_token)
+            return page
+        else:
+            return None
+
+    def _has_next_page(self):
+        """Determines whether or not there are more pages with results.
+
+        Returns:
+            bool: Whether the iterator has more pages.
+        """
+        if self.page_number == 0:
+            return True
+
+        if self.max_results is not None:
+            if self.num_results >= self.max_results:
+                return False
+
+        return self.next_page_token is not None
+
+    def _get_query_params(self):
+        """Getter for query parameters for the next request.
+
+        Returns:
+            dict: A dictionary of query parameters.
+        """
+        result = {}
+        if self.next_page_token is not None:
+            result[self._PAGE_TOKEN] = self.next_page_token
+
+        page_size = None
+        if self.max_results is not None:
+            page_size = self.max_results - self.num_results
+            if self._page_size is not None:
+                page_size = min(page_size, self._page_size)
+        elif self._page_size is not None:
+            page_size = self._page_size
+
+        if page_size is not None:
+            result[self._MAX_RESULTS] = page_size
+
+        result.update(self.extra_params)
+        return result
+
+    def _get_next_page_response(self):
+        """Requests the next page from the path provided.
+
+        Returns:
+            dict: The parsed JSON response of the next page's contents.
+
+        Raises:
+            ValueError: If the HTTP method is not ``GET`` or ``POST``.
+        """
+        params = self._get_query_params()
+        if self._HTTP_METHOD == "GET":
+            return self.api_request(
+                method=self._HTTP_METHOD, path=self.path, query_params=params
+            )
+        elif self._HTTP_METHOD == "POST":
+            return self.api_request(
+                method=self._HTTP_METHOD, path=self.path, data=params
+            )
+        else:
+            raise ValueError("Unexpected HTTP method", self._HTTP_METHOD)
+
+
+class _GAXIterator(Iterator):
+    """A generic class for iterating through Cloud gRPC APIs list responses.
+
+    Any:
+        client (google.cloud.client.Client): The API client.
+        page_iter (google.gax.PageIterator): A GAX page iterator to be wrapped
+            to conform to the :class:`Iterator` interface.
+        item_to_value (Callable[Iterator, Any]): Callable to convert an item
+            from the the protobuf response into a native object. Will
+            be called with the iterator and a single item.
+        max_results (int): The maximum number of results to fetch.
+
+    .. autoattribute:: pages
+    """
+
+    def __init__(self, client, page_iter, item_to_value, max_results=None):
+        super(_GAXIterator, self).__init__(
+            client,
+            item_to_value,
+            page_token=page_iter.page_token,
+            max_results=max_results,
+        )
+        self._gax_page_iter = page_iter
+
+    def _next_page(self):
+        """Get the next page in the iterator.
+
+        Wraps the response from the :class:`~google.gax.PageIterator` in a
+        :class:`Page` instance and captures some state at each page.
+
+        Returns:
+            Optional[Page]: The next page in the iterator or :data:`None` if
+                  there are no pages left.
+        """
+        try:
+            items = next(self._gax_page_iter)
+            page = Page(self, items, self.item_to_value)
+            self.next_page_token = self._gax_page_iter.page_token or None
+            return page
+        except StopIteration:
+            return None
+
+
+class GRPCIterator(Iterator):
+    """A generic class for iterating through gRPC list responses.
+
+    .. note:: The class does not take a ``page_token`` argument because it can
+        just be specified in the ``request``.
+
+    Args:
+        client (google.cloud.client.Client): The API client. This unused by
+            this class, but kept to satisfy the :class:`Iterator` interface.
+        method (Callable[protobuf.Message]): A bound gRPC method that should
+            take a single message for the request.
+        request (protobuf.Message): The request message.
+        items_field (str): The field in the response message that has the
+            items for the page.
+        item_to_value (Callable[GRPCIterator, Any]): Callable to convert an
+            item from the type in the JSON response into a native object. Will
+            be called with the iterator and a single item.
+        request_token_field (str): The field in the request message used to
+            specify the page token.
+        response_token_field (str): The field in the response message that has
+            the token for the next page.
+        max_results (int): The maximum number of results to fetch.
+
+    .. autoattribute:: pages
+    """
+
+    _DEFAULT_REQUEST_TOKEN_FIELD = "page_token"
+    _DEFAULT_RESPONSE_TOKEN_FIELD = "next_page_token"
+
+    def __init__(
+        self,
+        client,
+        method,
+        request,
+        items_field,
+        item_to_value=_item_to_value_identity,
+        request_token_field=_DEFAULT_REQUEST_TOKEN_FIELD,
+        response_token_field=_DEFAULT_RESPONSE_TOKEN_FIELD,
+        max_results=None,
+    ):
+        super(GRPCIterator, self).__init__(
+            client, item_to_value, max_results=max_results
+        )
+        self._method = method
+        self._request = request
+        self._items_field = items_field
+        self._request_token_field = request_token_field
+        self._response_token_field = response_token_field
+
+    def _next_page(self):
+        """Get the next page in the iterator.
+
+        Returns:
+            Page: The next page in the iterator or :data:`None` if
+                there are no pages left.
+        """
+        if not self._has_next_page():
+            return None
+
+        if self.next_page_token is not None:
+            setattr(self._request, self._request_token_field, self.next_page_token)
+
+        response = self._method(self._request)
+
+        self.next_page_token = getattr(response, self._response_token_field)
+        items = getattr(response, self._items_field)
+        page = Page(self, items, self.item_to_value, raw_page=response)
+
+        return page
+
+    def _has_next_page(self):
+        """Determines whether or not there are more pages with results.
+
+        Returns:
+            bool: Whether the iterator has more pages.
+        """
+        if self.page_number == 0:
+            return True
+
+        if self.max_results is not None:
+            if self.num_results >= self.max_results:
+                return False
+
+        # Note: intentionally a falsy check instead of a None check. The RPC
+        # can return an empty string indicating no more pages.
+        return True if self.next_page_token else False
diff --git a/google/api_core/page_iterator_async.py b/google/api_core/page_iterator_async.py
new file mode 100644
index 0000000..c072575
--- /dev/null
+++ b/google/api_core/page_iterator_async.py
@@ -0,0 +1,285 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""AsyncIO iterators for paging through paged API methods.
+
+These iterators simplify the process of paging through API responses
+where the request takes a page token and the response is a list of results with
+a token for the next page. See `list pagination`_ in the Google API Style Guide
+for more details.
+
+.. _list pagination:
+    https://cloud.google.com/apis/design/design_patterns#list_pagination
+
+API clients that have methods that follow the list pagination pattern can
+return an :class:`.AsyncIterator`:
+
+    >>> results_iterator = await client.list_resources()
+
+Or you can walk your way through items and call off the search early if
+you find what you're looking for (resulting in possibly fewer requests)::
+
+    >>> async for resource in results_iterator:
+    ...     print(resource.name)
+    ...     if not resource.is_valid:
+    ...         break
+
+At any point, you may check the number of items consumed by referencing the
+``num_results`` property of the iterator::
+
+    >>> async for my_item in results_iterator:
+    ...     if results_iterator.num_results >= 10:
+    ...         break
+
+When iterating, not every new item will send a request to the server.
+To iterate based on each page of items (where a page corresponds to
+a request)::
+
+    >>> async for page in results_iterator.pages:
+    ...     print('=' * 20)
+    ...     print('    Page number: {:d}'.format(iterator.page_number))
+    ...     print('  Items in page: {:d}'.format(page.num_items))
+    ...     print('     First item: {!r}'.format(next(page)))
+    ...     print('Items remaining: {:d}'.format(page.remaining))
+    ...     print('Next page token: {}'.format(iterator.next_page_token))
+    ====================
+        Page number: 1
+      Items in page: 1
+         First item: <MyItemClass at 0x7f1d3cccf690>
+    Items remaining: 0
+    Next page token: eav1OzQB0OM8rLdGXOEsyQWSG
+    ====================
+        Page number: 2
+      Items in page: 19
+         First item: <MyItemClass at 0x7f1d3cccffd0>
+    Items remaining: 18
+    Next page token: None
+"""
+
+import abc
+
+from google.api_core.page_iterator import Page
+
+
+def _item_to_value_identity(iterator, item):
+    """An item to value transformer that returns the item un-changed."""
+    # pylint: disable=unused-argument
+    # We are conforming to the interface defined by Iterator.
+    return item
+
+
+class AsyncIterator(abc.ABC):
+    """A generic class for iterating through API list responses.
+
+    Args:
+        client(google.cloud.client.Client): The API client.
+        item_to_value (Callable[google.api_core.page_iterator_async.AsyncIterator, Any]):
+            Callable to convert an item from the type in the raw API response
+            into the native object. Will be called with the iterator and a
+            single item.
+        page_token (str): A token identifying a page in a result set to start
+            fetching results from.
+        max_results (int): The maximum number of results to fetch.
+    """
+
+    def __init__(
+        self,
+        client,
+        item_to_value=_item_to_value_identity,
+        page_token=None,
+        max_results=None,
+    ):
+        self._started = False
+        self.__active_aiterator = None
+
+        self.client = client
+        """Optional[Any]: The client that created this iterator."""
+        self.item_to_value = item_to_value
+        """Callable[Iterator, Any]: Callable to convert an item from the type
+            in the raw API response into the native object. Will be called with
+            the iterator and a
+            single item.
+        """
+        self.max_results = max_results
+        """int: The maximum number of results to fetch."""
+
+        # The attributes below will change over the life of the iterator.
+        self.page_number = 0
+        """int: The current page of results."""
+        self.next_page_token = page_token
+        """str: The token for the next page of results. If this is set before
+            the iterator starts, it effectively offsets the iterator to a
+            specific starting point."""
+        self.num_results = 0
+        """int: The total number of results fetched so far."""
+
+    @property
+    def pages(self):
+        """Iterator of pages in the response.
+
+        returns:
+            types.GeneratorType[google.api_core.page_iterator.Page]: A
+                generator of page instances.
+
+        raises:
+            ValueError: If the iterator has already been started.
+        """
+        if self._started:
+            raise ValueError("Iterator has already started", self)
+        self._started = True
+        return self._page_aiter(increment=True)
+
+    async def _items_aiter(self):
+        """Iterator for each item returned."""
+        async for page in self._page_aiter(increment=False):
+            for item in page:
+                self.num_results += 1
+                yield item
+
+    def __aiter__(self):
+        """Iterator for each item returned.
+
+        Returns:
+            types.GeneratorType[Any]: A generator of items from the API.
+
+        Raises:
+            ValueError: If the iterator has already been started.
+        """
+        if self._started:
+            raise ValueError("Iterator has already started", self)
+        self._started = True
+        return self._items_aiter()
+
+    async def __anext__(self):
+        if self.__active_aiterator is None:
+            self.__active_aiterator = self.__aiter__()
+        return await self.__active_aiterator.__anext__()
+
+    async def _page_aiter(self, increment):
+        """Generator of pages of API responses.
+
+        Args:
+            increment (bool): Flag indicating if the total number of results
+                should be incremented on each page. This is useful since a page
+                iterator will want to increment by results per page while an
+                items iterator will want to increment per item.
+
+        Yields:
+            Page: each page of items from the API.
+        """
+        page = await self._next_page()
+        while page is not None:
+            self.page_number += 1
+            if increment:
+                self.num_results += page.num_items
+            yield page
+            page = await self._next_page()
+
+    @abc.abstractmethod
+    async def _next_page(self):
+        """Get the next page in the iterator.
+
+        This does nothing and is intended to be over-ridden by subclasses
+        to return the next :class:`Page`.
+
+        Raises:
+            NotImplementedError: Always, this method is abstract.
+        """
+        raise NotImplementedError
+
+
+class AsyncGRPCIterator(AsyncIterator):
+    """A generic class for iterating through gRPC list responses.
+
+    .. note:: The class does not take a ``page_token`` argument because it can
+        just be specified in the ``request``.
+
+    Args:
+        client (google.cloud.client.Client): The API client. This unused by
+            this class, but kept to satisfy the :class:`Iterator` interface.
+        method (Callable[protobuf.Message]): A bound gRPC method that should
+            take a single message for the request.
+        request (protobuf.Message): The request message.
+        items_field (str): The field in the response message that has the
+            items for the page.
+        item_to_value (Callable[GRPCIterator, Any]): Callable to convert an
+            item from the type in the JSON response into a native object. Will
+            be called with the iterator and a single item.
+        request_token_field (str): The field in the request message used to
+            specify the page token.
+        response_token_field (str): The field in the response message that has
+            the token for the next page.
+        max_results (int): The maximum number of results to fetch.
+
+    .. autoattribute:: pages
+    """
+
+    _DEFAULT_REQUEST_TOKEN_FIELD = "page_token"
+    _DEFAULT_RESPONSE_TOKEN_FIELD = "next_page_token"
+
+    def __init__(
+        self,
+        client,
+        method,
+        request,
+        items_field,
+        item_to_value=_item_to_value_identity,
+        request_token_field=_DEFAULT_REQUEST_TOKEN_FIELD,
+        response_token_field=_DEFAULT_RESPONSE_TOKEN_FIELD,
+        max_results=None,
+    ):
+        super().__init__(client, item_to_value, max_results=max_results)
+        self._method = method
+        self._request = request
+        self._items_field = items_field
+        self._request_token_field = request_token_field
+        self._response_token_field = response_token_field
+
+    async def _next_page(self):
+        """Get the next page in the iterator.
+
+        Returns:
+            Page: The next page in the iterator or :data:`None` if
+                there are no pages left.
+        """
+        if not self._has_next_page():
+            return None
+
+        if self.next_page_token is not None:
+            setattr(self._request, self._request_token_field, self.next_page_token)
+
+        response = await self._method(self._request)
+
+        self.next_page_token = getattr(response, self._response_token_field)
+        items = getattr(response, self._items_field)
+        page = Page(self, items, self.item_to_value, raw_page=response)
+
+        return page
+
+    def _has_next_page(self):
+        """Determines whether or not there are more pages with results.
+
+        Returns:
+            bool: Whether the iterator has more pages.
+        """
+        if self.page_number == 0:
+            return True
+
+        # Note: intentionally a falsy check instead of a None check. The RPC
+        # can return an empty string indicating no more pages.
+        if self.max_results is not None:
+            if self.num_results >= self.max_results:
+                return False
+
+        return True if self.next_page_token else False
diff --git a/google/api_core/path_template.py b/google/api_core/path_template.py
new file mode 100644
index 0000000..41fbd4f
--- /dev/null
+++ b/google/api_core/path_template.py
@@ -0,0 +1,300 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Expand and validate URL path templates.
+
+This module provides the :func:`expand` and :func:`validate` functions for
+interacting with Google-style URL `path templates`_ which are commonly used
+in Google APIs for `resource names`_.
+
+.. _path templates: https://github.com/googleapis/googleapis/blob
+    /57e2d376ac7ef48681554204a3ba78a414f2c533/google/api/http.proto#L212
+.. _resource names: https://cloud.google.com/apis/design/resource_names
+"""
+
+from __future__ import unicode_literals
+
+from collections import deque
+import copy
+import functools
+import re
+
+# Regular expression for extracting variable parts from a path template.
+# The variables can be expressed as:
+#
+# - "*": a single-segment positional variable, for example: "books/*"
+# - "**": a multi-segment positional variable, for example: "shelf/**/book/*"
+# - "{name}": a single-segment wildcard named variable, for example
+#   "books/{name}"
+# - "{name=*}: same as above.
+# - "{name=**}": a multi-segment wildcard named variable, for example
+#   "shelf/{name=**}"
+# - "{name=/path/*/**}": a multi-segment named variable with a sub-template.
+_VARIABLE_RE = re.compile(
+    r"""
+    (  # Capture the entire variable expression
+        (?P<positional>\*\*?)  # Match & capture * and ** positional variables.
+        |
+        # Match & capture named variables {name}
+        {
+            (?P<name>[^/]+?)
+            # Optionally match and capture the named variable's template.
+            (?:=(?P<template>.+?))?
+        }
+    )
+    """,
+    re.VERBOSE,
+)
+
+# Segment expressions used for validating paths against a template.
+_SINGLE_SEGMENT_PATTERN = r"([^/]+)"
+_MULTI_SEGMENT_PATTERN = r"(.+)"
+
+
+def _expand_variable_match(positional_vars, named_vars, match):
+    """Expand a matched variable with its value.
+
+    Args:
+        positional_vars (list): A list of positional variables. This list will
+            be modified.
+        named_vars (dict): A dictionary of named variables.
+        match (re.Match): A regular expression match.
+
+    Returns:
+        str: The expanded variable to replace the match.
+
+    Raises:
+        ValueError: If a positional or named variable is required by the
+            template but not specified or if an unexpected template expression
+            is encountered.
+    """
+    positional = match.group("positional")
+    name = match.group("name")
+    if name is not None:
+        try:
+            return str(named_vars[name])
+        except KeyError:
+            raise ValueError(
+                "Named variable '{}' not specified and needed by template "
+                "`{}` at position {}".format(name, match.string, match.start())
+            )
+    elif positional is not None:
+        try:
+            return str(positional_vars.pop(0))
+        except IndexError:
+            raise ValueError(
+                "Positional variable not specified and needed by template "
+                "`{}` at position {}".format(match.string, match.start())
+            )
+    else:
+        raise ValueError("Unknown template expression {}".format(match.group(0)))
+
+
+def expand(tmpl, *args, **kwargs):
+    """Expand a path template with the given variables.
+
+    .. code-block:: python
+
+        >>> expand('users/*/messages/*', 'me', '123')
+        users/me/messages/123
+        >>> expand('/v1/{name=shelves/*/books/*}', name='shelves/1/books/3')
+        /v1/shelves/1/books/3
+
+    Args:
+        tmpl (str): The path template.
+        args: The positional variables for the path.
+        kwargs: The named variables for the path.
+
+    Returns:
+        str: The expanded path
+
+    Raises:
+        ValueError: If a positional or named variable is required by the
+            template but not specified or if an unexpected template expression
+            is encountered.
+    """
+    replacer = functools.partial(_expand_variable_match, list(args), kwargs)
+    return _VARIABLE_RE.sub(replacer, tmpl)
+
+
+def _replace_variable_with_pattern(match):
+    """Replace a variable match with a pattern that can be used to validate it.
+
+    Args:
+        match (re.Match): A regular expression match
+
+    Returns:
+        str: A regular expression pattern that can be used to validate the
+            variable in an expanded path.
+
+    Raises:
+        ValueError: If an unexpected template expression is encountered.
+    """
+    positional = match.group("positional")
+    name = match.group("name")
+    template = match.group("template")
+    if name is not None:
+        if not template:
+            return _SINGLE_SEGMENT_PATTERN.format(name)
+        elif template == "**":
+            return _MULTI_SEGMENT_PATTERN.format(name)
+        else:
+            return _generate_pattern_for_template(template)
+    elif positional == "*":
+        return _SINGLE_SEGMENT_PATTERN
+    elif positional == "**":
+        return _MULTI_SEGMENT_PATTERN
+    else:
+        raise ValueError("Unknown template expression {}".format(match.group(0)))
+
+
+def _generate_pattern_for_template(tmpl):
+    """Generate a pattern that can validate a path template.
+
+    Args:
+        tmpl (str): The path template
+
+    Returns:
+        str: A regular expression pattern that can be used to validate an
+            expanded path template.
+    """
+    return _VARIABLE_RE.sub(_replace_variable_with_pattern, tmpl)
+
+
+def get_field(request, field):
+    """Get the value of a field from a given dictionary.
+
+    Args:
+        request (dict): A dictionary object.
+        field (str): The key to the request in dot notation.
+
+    Returns:
+        The value of the field.
+    """
+    parts = field.split(".")
+    value = request
+    for part in parts:
+        if not isinstance(value, dict):
+            return
+        value = value.get(part)
+    if isinstance(value, dict):
+        return
+    return value
+
+
+def delete_field(request, field):
+    """Delete the value of a field from a given dictionary.
+
+    Args:
+        request (dict): A dictionary object.
+        field (str): The key to the request in dot notation.
+    """
+    parts = deque(field.split("."))
+    while len(parts) > 1:
+        if not isinstance(request, dict):
+            return
+        part = parts.popleft()
+        request = request.get(part)
+    part = parts.popleft()
+    if not isinstance(request, dict):
+        return
+    request.pop(part, None)
+
+
+def validate(tmpl, path):
+    """Validate a path against the path template.
+
+    .. code-block:: python
+
+        >>> validate('users/*/messages/*', 'users/me/messages/123')
+        True
+        >>> validate('users/*/messages/*', 'users/me/drafts/123')
+        False
+        >>> validate('/v1/{name=shelves/*/books/*}', /v1/shelves/1/books/3)
+        True
+        >>> validate('/v1/{name=shelves/*/books/*}', /v1/shelves/1/tapes/3)
+        False
+
+    Args:
+        tmpl (str): The path template.
+        path (str): The expanded path.
+
+    Returns:
+        bool: True if the path matches.
+    """
+    pattern = _generate_pattern_for_template(tmpl) + "$"
+    return True if re.match(pattern, path) is not None else False
+
+
+def transcode(http_options, **request_kwargs):
+    """Transcodes a grpc request pattern into a proper HTTP request following the rules outlined here,
+       https://github.com/googleapis/googleapis/blob/master/google/api/http.proto#L44-L312
+
+        Args:
+            http_options (list(dict)): A list of dicts which consist of these keys,
+                'method'    (str): The http method
+                'uri'       (str): The path template
+                'body'      (str): The body field name (optional)
+                (This is a simplified representation of the proto option `google.api.http`)
+
+            request_kwargs (dict) : A dict representing the request object
+
+        Returns:
+            dict: The transcoded request with these keys,
+                'method'        (str)   : The http method
+                'uri'           (str)   : The expanded uri
+                'body'          (dict)  : A dict representing the body (optional)
+                'query_params'  (dict)  : A dict mapping query parameter variables and values
+
+        Raises:
+            ValueError: If the request does not match the given template.
+    """
+    for http_option in http_options:
+        request = {}
+
+        # Assign path
+        uri_template = http_option["uri"]
+        path_fields = [
+            match.group("name") for match in _VARIABLE_RE.finditer(uri_template)
+        ]
+        path_args = {field: get_field(request_kwargs, field) for field in path_fields}
+        request["uri"] = expand(uri_template, **path_args)
+
+        # Remove fields used in uri path from request
+        leftovers = copy.deepcopy(request_kwargs)
+        for path_field in path_fields:
+            delete_field(leftovers, path_field)
+
+        if not validate(uri_template, request["uri"]) or not all(path_args.values()):
+            continue
+
+        # Assign body and query params
+        body = http_option.get("body")
+
+        if body:
+            if body == "*":
+                request["body"] = leftovers
+                request["query_params"] = {}
+            else:
+                try:
+                    request["body"] = leftovers.pop(body)
+                except KeyError:
+                    continue
+                request["query_params"] = leftovers
+        else:
+            request["query_params"] = leftovers
+        request["method"] = http_option["method"]
+        return request
+
+    raise ValueError("Request obj does not match any template")
diff --git a/google/api_core/protobuf_helpers.py b/google/api_core/protobuf_helpers.py
new file mode 100644
index 0000000..896e89c
--- /dev/null
+++ b/google/api_core/protobuf_helpers.py
@@ -0,0 +1,373 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helpers for :mod:`protobuf`."""
+
+import collections
+import collections.abc
+import copy
+import inspect
+
+from google.protobuf import field_mask_pb2
+from google.protobuf import message
+from google.protobuf import wrappers_pb2
+
+
+_SENTINEL = object()
+_WRAPPER_TYPES = (
+    wrappers_pb2.BoolValue,
+    wrappers_pb2.BytesValue,
+    wrappers_pb2.DoubleValue,
+    wrappers_pb2.FloatValue,
+    wrappers_pb2.Int32Value,
+    wrappers_pb2.Int64Value,
+    wrappers_pb2.StringValue,
+    wrappers_pb2.UInt32Value,
+    wrappers_pb2.UInt64Value,
+)
+
+
+def from_any_pb(pb_type, any_pb):
+    """Converts an ``Any`` protobuf to the specified message type.
+
+    Args:
+        pb_type (type): the type of the message that any_pb stores an instance
+            of.
+        any_pb (google.protobuf.any_pb2.Any): the object to be converted.
+
+    Returns:
+        pb_type: An instance of the pb_type message.
+
+    Raises:
+        TypeError: if the message could not be converted.
+    """
+    msg = pb_type()
+
+    # Unwrap proto-plus wrapped messages.
+    if callable(getattr(pb_type, "pb", None)):
+        msg_pb = pb_type.pb(msg)
+    else:
+        msg_pb = msg
+
+    # Unpack the Any object and populate the protobuf message instance.
+    if not any_pb.Unpack(msg_pb):
+        raise TypeError(
+            "Could not convert {} to {}".format(
+                any_pb.__class__.__name__, pb_type.__name__
+            )
+        )
+
+    # Done; return the message.
+    return msg
+
+
+def check_oneof(**kwargs):
+    """Raise ValueError if more than one keyword argument is not ``None``.
+
+    Args:
+        kwargs (dict): The keyword arguments sent to the function.
+
+    Raises:
+        ValueError: If more than one entry in ``kwargs`` is not ``None``.
+    """
+    # Sanity check: If no keyword arguments were sent, this is fine.
+    if not kwargs:
+        return
+
+    not_nones = [val for val in kwargs.values() if val is not None]
+    if len(not_nones) > 1:
+        raise ValueError(
+            "Only one of {fields} should be set.".format(
+                fields=", ".join(sorted(kwargs.keys()))
+            )
+        )
+
+
+def get_messages(module):
+    """Discovers all protobuf Message classes in a given import module.
+
+    Args:
+        module (module): A Python module; :func:`dir` will be run against this
+            module to find Message subclasses.
+
+    Returns:
+        dict[str, google.protobuf.message.Message]: A dictionary with the
+            Message class names as keys, and the Message subclasses themselves
+            as values.
+    """
+    answer = collections.OrderedDict()
+    for name in dir(module):
+        candidate = getattr(module, name)
+        if inspect.isclass(candidate) and issubclass(candidate, message.Message):
+            answer[name] = candidate
+    return answer
+
+
+def _resolve_subkeys(key, separator="."):
+    """Resolve a potentially nested key.
+
+    If the key contains the ``separator`` (e.g. ``.``) then the key will be
+    split on the first instance of the subkey::
+
+       >>> _resolve_subkeys('a.b.c')
+       ('a', 'b.c')
+       >>> _resolve_subkeys('d|e|f', separator='|')
+       ('d', 'e|f')
+
+    If not, the subkey will be :data:`None`::
+
+        >>> _resolve_subkeys('foo')
+        ('foo', None)
+
+    Args:
+        key (str): A string that may or may not contain the separator.
+        separator (str): The namespace separator. Defaults to `.`.
+
+    Returns:
+        Tuple[str, str]: The key and subkey(s).
+    """
+    parts = key.split(separator, 1)
+
+    if len(parts) > 1:
+        return parts
+    else:
+        return parts[0], None
+
+
+def get(msg_or_dict, key, default=_SENTINEL):
+    """Retrieve a key's value from a protobuf Message or dictionary.
+
+    Args:
+        mdg_or_dict (Union[~google.protobuf.message.Message, Mapping]): the
+            object.
+        key (str): The key to retrieve from the object.
+        default (Any): If the key is not present on the object, and a default
+            is set, returns that default instead. A type-appropriate falsy
+            default is generally recommended, as protobuf messages almost
+            always have default values for unset values and it is not always
+            possible to tell the difference between a falsy value and an
+            unset one. If no default is set then :class:`KeyError` will be
+            raised if the key is not present in the object.
+
+    Returns:
+        Any: The return value from the underlying Message or dict.
+
+    Raises:
+        KeyError: If the key is not found. Note that, for unset values,
+            messages and dictionaries may not have consistent behavior.
+        TypeError: If ``msg_or_dict`` is not a Message or Mapping.
+    """
+    # We may need to get a nested key. Resolve this.
+    key, subkey = _resolve_subkeys(key)
+
+    # Attempt to get the value from the two types of objects we know about.
+    # If we get something else, complain.
+    if isinstance(msg_or_dict, message.Message):
+        answer = getattr(msg_or_dict, key, default)
+    elif isinstance(msg_or_dict, collections.abc.Mapping):
+        answer = msg_or_dict.get(key, default)
+    else:
+        raise TypeError(
+            "get() expected a dict or protobuf message, got {!r}.".format(
+                type(msg_or_dict)
+            )
+        )
+
+    # If the object we got back is our sentinel, raise KeyError; this is
+    # a "not found" case.
+    if answer is _SENTINEL:
+        raise KeyError(key)
+
+    # If a subkey exists, call this method recursively against the answer.
+    if subkey is not None and answer is not default:
+        return get(answer, subkey, default=default)
+
+    return answer
+
+
+def _set_field_on_message(msg, key, value):
+    """Set helper for protobuf Messages."""
+    # Attempt to set the value on the types of objects we know how to deal
+    # with.
+    if isinstance(value, (collections.abc.MutableSequence, tuple)):
+        # Clear the existing repeated protobuf message of any elements
+        # currently inside it.
+        while getattr(msg, key):
+            getattr(msg, key).pop()
+
+        # Write our new elements to the repeated field.
+        for item in value:
+            if isinstance(item, collections.abc.Mapping):
+                getattr(msg, key).add(**item)
+            else:
+                # protobuf's RepeatedCompositeContainer doesn't support
+                # append.
+                getattr(msg, key).extend([item])
+    elif isinstance(value, collections.abc.Mapping):
+        # Assign the dictionary values to the protobuf message.
+        for item_key, item_value in value.items():
+            set(getattr(msg, key), item_key, item_value)
+    elif isinstance(value, message.Message):
+        getattr(msg, key).CopyFrom(value)
+    else:
+        setattr(msg, key, value)
+
+
+def set(msg_or_dict, key, value):
+    """Set a key's value on a protobuf Message or dictionary.
+
+    Args:
+        msg_or_dict (Union[~google.protobuf.message.Message, Mapping]): the
+            object.
+        key (str): The key to set.
+        value (Any): The value to set.
+
+    Raises:
+        TypeError: If ``msg_or_dict`` is not a Message or dictionary.
+    """
+    # Sanity check: Is our target object valid?
+    if not isinstance(msg_or_dict, (collections.abc.MutableMapping, message.Message)):
+        raise TypeError(
+            "set() expected a dict or protobuf message, got {!r}.".format(
+                type(msg_or_dict)
+            )
+        )
+
+    # We may be setting a nested key. Resolve this.
+    basekey, subkey = _resolve_subkeys(key)
+
+    # If a subkey exists, then get that object and call this method
+    # recursively against it using the subkey.
+    if subkey is not None:
+        if isinstance(msg_or_dict, collections.abc.MutableMapping):
+            msg_or_dict.setdefault(basekey, {})
+        set(get(msg_or_dict, basekey), subkey, value)
+        return
+
+    if isinstance(msg_or_dict, collections.abc.MutableMapping):
+        msg_or_dict[key] = value
+    else:
+        _set_field_on_message(msg_or_dict, key, value)
+
+
+def setdefault(msg_or_dict, key, value):
+    """Set the key on a protobuf Message or dictionary to a given value if the
+    current value is falsy.
+
+    Because protobuf Messages do not distinguish between unset values and
+    falsy ones particularly well (by design), this method treats any falsy
+    value (e.g. 0, empty list) as a target to be overwritten, on both Messages
+    and dictionaries.
+
+    Args:
+        msg_or_dict (Union[~google.protobuf.message.Message, Mapping]): the
+            object.
+        key (str): The key on the object in question.
+        value (Any): The value to set.
+
+    Raises:
+        TypeError: If ``msg_or_dict`` is not a Message or dictionary.
+    """
+    if not get(msg_or_dict, key, default=None):
+        set(msg_or_dict, key, value)
+
+
+def field_mask(original, modified):
+    """Create a field mask by comparing two messages.
+
+    Args:
+        original (~google.protobuf.message.Message): the original message.
+            If set to None, this field will be interpretted as an empty
+            message.
+        modified (~google.protobuf.message.Message): the modified message.
+            If set to None, this field will be interpretted as an empty
+            message.
+
+    Returns:
+        google.protobuf.field_mask_pb2.FieldMask: field mask that contains
+        the list of field names that have different values between the two
+        messages. If the messages are equivalent, then the field mask is empty.
+
+    Raises:
+        ValueError: If the ``original`` or ``modified`` are not the same type.
+    """
+    if original is None and modified is None:
+        return field_mask_pb2.FieldMask()
+
+    if original is None and modified is not None:
+        original = copy.deepcopy(modified)
+        original.Clear()
+
+    if modified is None and original is not None:
+        modified = copy.deepcopy(original)
+        modified.Clear()
+
+    if type(original) != type(modified):
+        raise ValueError(
+            "expected that both original and modified should be of the "
+            'same type, received "{!r}" and "{!r}".'.format(
+                type(original), type(modified)
+            )
+        )
+
+    return field_mask_pb2.FieldMask(paths=_field_mask_helper(original, modified))
+
+
+def _field_mask_helper(original, modified, current=""):
+    answer = []
+
+    for name in original.DESCRIPTOR.fields_by_name:
+        field_path = _get_path(current, name)
+
+        original_val = getattr(original, name)
+        modified_val = getattr(modified, name)
+
+        if _is_message(original_val) or _is_message(modified_val):
+            if original_val != modified_val:
+                # Wrapper types do not need to include the .value part of the
+                # path.
+                if _is_wrapper(original_val) or _is_wrapper(modified_val):
+                    answer.append(field_path)
+                elif not modified_val.ListFields():
+                    answer.append(field_path)
+                else:
+                    answer.extend(
+                        _field_mask_helper(original_val, modified_val, field_path)
+                    )
+        else:
+            if original_val != modified_val:
+                answer.append(field_path)
+
+    return answer
+
+
+def _get_path(current, name):
+    # gapic-generator-python appends underscores to field names
+    # that collide with python keywords.
+    # `_` is stripped away as it is not possible to
+    # natively define a field with a trailing underscore in protobuf.
+    # APIs will reject field masks if fields have trailing underscores.
+    # See https://github.com/googleapis/python-api-core/issues/227
+    name = name.rstrip("_")
+    if not current:
+        return name
+    return "%s.%s" % (current, name)
+
+
+def _is_message(value):
+    return isinstance(value, message.Message)
+
+
+def _is_wrapper(value):
+    return type(value) in _WRAPPER_TYPES
diff --git a/google/api_core/py.typed b/google/api_core/py.typed
new file mode 100644
index 0000000..1d5517b
--- /dev/null
+++ b/google/api_core/py.typed
@@ -0,0 +1,2 @@
+# Marker file for PEP 561.
+# The google-api-core package uses inline types.
diff --git a/google/api_core/rest_helpers.py b/google/api_core/rest_helpers.py
new file mode 100644
index 0000000..23fb614
--- /dev/null
+++ b/google/api_core/rest_helpers.py
@@ -0,0 +1,94 @@
+# Copyright 2021 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helpers for rest transports."""
+
+import functools
+import operator
+
+
+def flatten_query_params(obj):
+    """Flatten a nested dict into a list of (name,value) tuples.
+
+    The result is suitable for setting query params on an http request.
+
+    .. code-block:: python
+
+        >>> obj = {'a':
+        ...         {'b':
+        ...           {'c': ['x', 'y', 'z']} },
+        ...      'd': 'uvw', }
+        >>> flatten_query_params(obj)
+        [('a.b.c', 'x'), ('a.b.c', 'y'), ('a.b.c', 'z'), ('d', 'uvw')]
+
+    Note that, as described in
+    https://github.com/googleapis/googleapis/blob/48d9fb8c8e287c472af500221c6450ecd45d7d39/google/api/http.proto#L117,
+    repeated fields (i.e. list-valued fields) may only contain primitive types (not lists or dicts).
+    This is enforced in this function.
+
+    Args:
+      obj: a nested dictionary (from json), or None
+
+    Returns: a list of tuples, with each tuple having a (possibly) multi-part name
+      and a scalar value.
+
+    Raises:
+      TypeError if obj is not a dict or None
+      ValueError if obj contains a list of non-primitive values.
+    """
+
+    if obj is not None and not isinstance(obj, dict):
+        raise TypeError("flatten_query_params must be called with dict object")
+
+    return _flatten(obj, key_path=[])
+
+
+def _flatten(obj, key_path):
+    if obj is None:
+        return []
+    if isinstance(obj, dict):
+        return _flatten_dict(obj, key_path=key_path)
+    if isinstance(obj, list):
+        return _flatten_list(obj, key_path=key_path)
+    return _flatten_value(obj, key_path=key_path)
+
+
+def _is_primitive_value(obj):
+    if obj is None:
+        return False
+
+    if isinstance(obj, (list, dict)):
+        raise ValueError("query params may not contain repeated dicts or lists")
+
+    return True
+
+
+def _flatten_value(obj, key_path):
+    return [(".".join(key_path), obj)]
+
+
+def _flatten_dict(obj, key_path):
+    items = (_flatten(value, key_path=key_path + [key]) for key, value in obj.items())
+    return functools.reduce(operator.concat, items, [])
+
+
+def _flatten_list(elems, key_path):
+    # Only lists of scalar values are supported.
+    # The name (key_path) is repeated for each value.
+    items = (
+        _flatten_value(elem, key_path=key_path)
+        for elem in elems
+        if _is_primitive_value(elem)
+    )
+    return functools.reduce(operator.concat, items, [])
diff --git a/google/api_core/retry.py b/google/api_core/retry.py
new file mode 100644
index 0000000..bd3a4a6
--- /dev/null
+++ b/google/api_core/retry.py
@@ -0,0 +1,366 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helpers for retrying functions with exponential back-off.
+
+The :class:`Retry` decorator can be used to retry functions that raise
+exceptions using exponential backoff. Because a exponential sleep algorithm is
+used, the retry is limited by a `deadline`. The deadline is the maxmimum amount
+of time a method can block. This is used instead of total number of retries
+because it is difficult to ascertain the amount of time a function can block
+when using total number of retries and exponential backoff.
+
+By default, this decorator will retry transient
+API errors (see :func:`if_transient_error`). For example:
+
+.. code-block:: python
+
+    @retry.Retry()
+    def call_flaky_rpc():
+        return client.flaky_rpc()
+
+    # Will retry flaky_rpc() if it raises transient API errors.
+    result = call_flaky_rpc()
+
+You can pass a custom predicate to retry on different exceptions, such as
+waiting for an eventually consistent item to be available:
+
+.. code-block:: python
+
+    @retry.Retry(predicate=if_exception_type(exceptions.NotFound))
+    def check_if_exists():
+        return client.does_thing_exist()
+
+    is_available = check_if_exists()
+
+Some client library methods apply retry automatically. These methods can accept
+a ``retry`` parameter that allows you to configure the behavior:
+
+.. code-block:: python
+
+    my_retry = retry.Retry(deadline=60)
+    result = client.some_method(retry=my_retry)
+
+"""
+
+from __future__ import unicode_literals
+
+import datetime
+import functools
+import logging
+import random
+import time
+
+import requests.exceptions
+
+from google.api_core import datetime_helpers
+from google.api_core import exceptions
+from google.auth import exceptions as auth_exceptions
+
+_LOGGER = logging.getLogger(__name__)
+_DEFAULT_INITIAL_DELAY = 1.0  # seconds
+_DEFAULT_MAXIMUM_DELAY = 60.0  # seconds
+_DEFAULT_DELAY_MULTIPLIER = 2.0
+_DEFAULT_DEADLINE = 60.0 * 2.0  # seconds
+
+
+def if_exception_type(*exception_types):
+    """Creates a predicate to check if the exception is of a given type.
+
+    Args:
+        exception_types (Sequence[:func:`type`]): The exception types to check
+            for.
+
+    Returns:
+        Callable[Exception]: A predicate that returns True if the provided
+            exception is of the given type(s).
+    """
+
+    def if_exception_type_predicate(exception):
+        """Bound predicate for checking an exception type."""
+        return isinstance(exception, exception_types)
+
+    return if_exception_type_predicate
+
+
+# pylint: disable=invalid-name
+# Pylint sees this as a constant, but it is also an alias that should be
+# considered a function.
+if_transient_error = if_exception_type(
+    exceptions.InternalServerError,
+    exceptions.TooManyRequests,
+    exceptions.ServiceUnavailable,
+    requests.exceptions.ConnectionError,
+    requests.exceptions.ChunkedEncodingError,
+    auth_exceptions.TransportError,
+)
+"""A predicate that checks if an exception is a transient API error.
+
+The following server errors are considered transient:
+
+- :class:`google.api_core.exceptions.InternalServerError` - HTTP 500, gRPC
+    ``INTERNAL(13)`` and its subclasses.
+- :class:`google.api_core.exceptions.TooManyRequests` - HTTP 429
+- :class:`google.api_core.exceptions.ServiceUnavailable` - HTTP 503
+- :class:`requests.exceptions.ConnectionError`
+- :class:`requests.exceptions.ChunkedEncodingError` - The server declared
+    chunked encoding but sent an invalid chunk.
+- :class:`google.auth.exceptions.TransportError` - Used to indicate an
+    error occurred during an HTTP request.
+"""
+# pylint: enable=invalid-name
+
+
+def exponential_sleep_generator(initial, maximum, multiplier=_DEFAULT_DELAY_MULTIPLIER):
+    """Generates sleep intervals based on the exponential back-off algorithm.
+
+    This implements the `Truncated Exponential Back-off`_ algorithm.
+
+    .. _Truncated Exponential Back-off:
+        https://cloud.google.com/storage/docs/exponential-backoff
+
+    Args:
+        initial (float): The minimum amount of time to delay. This must
+            be greater than 0.
+        maximum (float): The maximum amount of time to delay.
+        multiplier (float): The multiplier applied to the delay.
+
+    Yields:
+        float: successive sleep intervals.
+    """
+    delay = initial
+    while True:
+        # Introduce jitter by yielding a delay that is uniformly distributed
+        # to average out to the delay time.
+        yield min(random.uniform(0.0, delay * 2.0), maximum)
+        delay = delay * multiplier
+
+
+def retry_target(target, predicate, sleep_generator, deadline, on_error=None):
+    """Call a function and retry if it fails.
+
+    This is the lowest-level retry helper. Generally, you'll use the
+    higher-level retry helper :class:`Retry`.
+
+    Args:
+        target(Callable): The function to call and retry. This must be a
+            nullary function - apply arguments with `functools.partial`.
+        predicate (Callable[Exception]): A callable used to determine if an
+            exception raised by the target should be considered retryable.
+            It should return True to retry or False otherwise.
+        sleep_generator (Iterable[float]): An infinite iterator that determines
+            how long to sleep between retries.
+        deadline (float): How long to keep retrying the target. The last sleep
+            period is shortened as necessary, so that the last retry runs at
+            ``deadline`` (and not considerably beyond it).
+        on_error (Callable[Exception]): A function to call while processing a
+            retryable exception.  Any error raised by this function will *not*
+            be caught.
+
+    Returns:
+        Any: the return value of the target function.
+
+    Raises:
+        google.api_core.RetryError: If the deadline is exceeded while retrying.
+        ValueError: If the sleep generator stops yielding values.
+        Exception: If the target raises a method that isn't retryable.
+    """
+    if deadline is not None:
+        deadline_datetime = datetime_helpers.utcnow() + datetime.timedelta(
+            seconds=deadline
+        )
+    else:
+        deadline_datetime = None
+
+    last_exc = None
+
+    for sleep in sleep_generator:
+        try:
+            return target()
+
+        # pylint: disable=broad-except
+        # This function explicitly must deal with broad exceptions.
+        except Exception as exc:
+            if not predicate(exc):
+                raise
+            last_exc = exc
+            if on_error is not None:
+                on_error(exc)
+
+        now = datetime_helpers.utcnow()
+
+        if deadline_datetime is not None:
+            if deadline_datetime <= now:
+                raise exceptions.RetryError(
+                    "Deadline of {:.1f}s exceeded while calling {}".format(
+                        deadline, target
+                    ),
+                    last_exc,
+                ) from last_exc
+            else:
+                time_to_deadline = (deadline_datetime - now).total_seconds()
+                sleep = min(time_to_deadline, sleep)
+
+        _LOGGER.debug(
+            "Retrying due to {}, sleeping {:.1f}s ...".format(last_exc, sleep)
+        )
+        time.sleep(sleep)
+
+    raise ValueError("Sleep generator stopped yielding sleep values.")
+
+
+class Retry(object):
+    """Exponential retry decorator.
+
+    This class is a decorator used to add exponential back-off retry behavior
+    to an RPC call.
+
+    Although the default behavior is to retry transient API errors, a
+    different predicate can be provided to retry other exceptions.
+
+    Args:
+        predicate (Callable[Exception]): A callable that should return ``True``
+            if the given exception is retryable.
+        initial (float): The minimum amount of time to delay in seconds. This
+            must be greater than 0.
+        maximum (float): The maximum amount of time to delay in seconds.
+        multiplier (float): The multiplier applied to the delay.
+        deadline (float): How long to keep retrying in seconds. The last sleep
+            period is shortened as necessary, so that the last retry runs at
+            ``deadline`` (and not considerably beyond it).
+    """
+
+    def __init__(
+        self,
+        predicate=if_transient_error,
+        initial=_DEFAULT_INITIAL_DELAY,
+        maximum=_DEFAULT_MAXIMUM_DELAY,
+        multiplier=_DEFAULT_DELAY_MULTIPLIER,
+        deadline=_DEFAULT_DEADLINE,
+        on_error=None,
+    ):
+        self._predicate = predicate
+        self._initial = initial
+        self._multiplier = multiplier
+        self._maximum = maximum
+        self._deadline = deadline
+        self._on_error = on_error
+
+    def __call__(self, func, on_error=None):
+        """Wrap a callable with retry behavior.
+
+        Args:
+            func (Callable): The callable to add retry behavior to.
+            on_error (Callable[Exception]): A function to call while processing
+                a retryable exception. Any error raised by this function will
+                *not* be caught.
+
+        Returns:
+            Callable: A callable that will invoke ``func`` with retry
+                behavior.
+        """
+        if self._on_error is not None:
+            on_error = self._on_error
+
+        @functools.wraps(func)
+        def retry_wrapped_func(*args, **kwargs):
+            """A wrapper that calls target function with retry."""
+            target = functools.partial(func, *args, **kwargs)
+            sleep_generator = exponential_sleep_generator(
+                self._initial, self._maximum, multiplier=self._multiplier
+            )
+            return retry_target(
+                target,
+                self._predicate,
+                sleep_generator,
+                self._deadline,
+                on_error=on_error,
+            )
+
+        return retry_wrapped_func
+
+    @property
+    def deadline(self):
+        return self._deadline
+
+    def with_deadline(self, deadline):
+        """Return a copy of this retry with the given deadline.
+
+        Args:
+            deadline (float): How long to keep retrying.
+
+        Returns:
+            Retry: A new retry instance with the given deadline.
+        """
+        return Retry(
+            predicate=self._predicate,
+            initial=self._initial,
+            maximum=self._maximum,
+            multiplier=self._multiplier,
+            deadline=deadline,
+            on_error=self._on_error,
+        )
+
+    def with_predicate(self, predicate):
+        """Return a copy of this retry with the given predicate.
+
+        Args:
+            predicate (Callable[Exception]): A callable that should return
+                ``True`` if the given exception is retryable.
+
+        Returns:
+            Retry: A new retry instance with the given predicate.
+        """
+        return Retry(
+            predicate=predicate,
+            initial=self._initial,
+            maximum=self._maximum,
+            multiplier=self._multiplier,
+            deadline=self._deadline,
+            on_error=self._on_error,
+        )
+
+    def with_delay(self, initial=None, maximum=None, multiplier=None):
+        """Return a copy of this retry with the given delay options.
+
+        Args:
+            initial (float): The minimum amount of time to delay. This must
+                be greater than 0.
+            maximum (float): The maximum amount of time to delay.
+            multiplier (float): The multiplier applied to the delay.
+
+        Returns:
+            Retry: A new retry instance with the given predicate.
+        """
+        return Retry(
+            predicate=self._predicate,
+            initial=initial if initial is not None else self._initial,
+            maximum=maximum if maximum is not None else self._maximum,
+            multiplier=multiplier if multiplier is not None else self._multiplier,
+            deadline=self._deadline,
+            on_error=self._on_error,
+        )
+
+    def __str__(self):
+        return (
+            "<Retry predicate={}, initial={:.1f}, maximum={:.1f}, "
+            "multiplier={:.1f}, deadline={:.1f}, on_error={}>".format(
+                self._predicate,
+                self._initial,
+                self._maximum,
+                self._multiplier,
+                self._deadline,
+                self._on_error,
+            )
+        )
diff --git a/google/api_core/retry_async.py b/google/api_core/retry_async.py
new file mode 100644
index 0000000..2dfa2f6
--- /dev/null
+++ b/google/api_core/retry_async.py
@@ -0,0 +1,291 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Helpers for retrying coroutine functions with exponential back-off.
+
+The :class:`AsyncRetry` decorator shares most functionality and behavior with
+:class:`Retry`, but supports coroutine functions. Please refer to description
+of :class:`Retry` for more details.
+
+By default, this decorator will retry transient
+API errors (see :func:`if_transient_error`). For example:
+
+.. code-block:: python
+
+    @retry_async.AsyncRetry()
+    async def call_flaky_rpc():
+        return await client.flaky_rpc()
+
+    # Will retry flaky_rpc() if it raises transient API errors.
+    result = await call_flaky_rpc()
+
+You can pass a custom predicate to retry on different exceptions, such as
+waiting for an eventually consistent item to be available:
+
+.. code-block:: python
+
+    @retry_async.AsyncRetry(predicate=retry_async.if_exception_type(exceptions.NotFound))
+    async def check_if_exists():
+        return await client.does_thing_exist()
+
+    is_available = await check_if_exists()
+
+Some client library methods apply retry automatically. These methods can accept
+a ``retry`` parameter that allows you to configure the behavior:
+
+.. code-block:: python
+
+    my_retry = retry_async.AsyncRetry(deadline=60)
+    result = await client.some_method(retry=my_retry)
+
+"""
+
+import asyncio
+import datetime
+import functools
+import logging
+
+from google.api_core import datetime_helpers
+from google.api_core import exceptions
+from google.api_core.retry import exponential_sleep_generator
+from google.api_core.retry import if_exception_type  # noqa: F401
+from google.api_core.retry import if_transient_error
+
+
+_LOGGER = logging.getLogger(__name__)
+_DEFAULT_INITIAL_DELAY = 1.0  # seconds
+_DEFAULT_MAXIMUM_DELAY = 60.0  # seconds
+_DEFAULT_DELAY_MULTIPLIER = 2.0
+_DEFAULT_DEADLINE = 60.0 * 2.0  # seconds
+
+
+async def retry_target(target, predicate, sleep_generator, deadline, on_error=None):
+    """Call a function and retry if it fails.
+
+    This is the lowest-level retry helper. Generally, you'll use the
+    higher-level retry helper :class:`Retry`.
+
+    Args:
+        target(Callable): The function to call and retry. This must be a
+            nullary function - apply arguments with `functools.partial`.
+        predicate (Callable[Exception]): A callable used to determine if an
+            exception raised by the target should be considered retryable.
+            It should return True to retry or False otherwise.
+        sleep_generator (Iterable[float]): An infinite iterator that determines
+            how long to sleep between retries.
+        deadline (float): How long to keep retrying the target. The last sleep
+            period is shortened as necessary, so that the last retry runs at
+            ``deadline`` (and not considerably beyond it).
+        on_error (Callable[Exception]): A function to call while processing a
+            retryable exception.  Any error raised by this function will *not*
+            be caught.
+
+    Returns:
+        Any: the return value of the target function.
+
+    Raises:
+        google.api_core.RetryError: If the deadline is exceeded while retrying.
+        ValueError: If the sleep generator stops yielding values.
+        Exception: If the target raises a method that isn't retryable.
+    """
+    deadline_dt = (
+        (datetime_helpers.utcnow() + datetime.timedelta(seconds=deadline))
+        if deadline
+        else None
+    )
+
+    last_exc = None
+
+    for sleep in sleep_generator:
+        try:
+            if not deadline_dt:
+                return await target()
+            else:
+                return await asyncio.wait_for(
+                    target(),
+                    timeout=(deadline_dt - datetime_helpers.utcnow()).total_seconds(),
+                )
+        # pylint: disable=broad-except
+        # This function explicitly must deal with broad exceptions.
+        except Exception as exc:
+            if not predicate(exc) and not isinstance(exc, asyncio.TimeoutError):
+                raise
+            last_exc = exc
+            if on_error is not None:
+                on_error(exc)
+
+        now = datetime_helpers.utcnow()
+
+        if deadline_dt:
+            if deadline_dt <= now:
+                # Chains the raising RetryError with the root cause error,
+                # which helps observability and debugability.
+                raise exceptions.RetryError(
+                    "Deadline of {:.1f}s exceeded while calling {}".format(
+                        deadline, target
+                    ),
+                    last_exc,
+                ) from last_exc
+            else:
+                time_to_deadline = (deadline_dt - now).total_seconds()
+                sleep = min(time_to_deadline, sleep)
+
+        _LOGGER.debug(
+            "Retrying due to {}, sleeping {:.1f}s ...".format(last_exc, sleep)
+        )
+        await asyncio.sleep(sleep)
+
+    raise ValueError("Sleep generator stopped yielding sleep values.")
+
+
+class AsyncRetry:
+    """Exponential retry decorator for async functions.
+
+    This class is a decorator used to add exponential back-off retry behavior
+    to an RPC call.
+
+    Although the default behavior is to retry transient API errors, a
+    different predicate can be provided to retry other exceptions.
+
+    Args:
+        predicate (Callable[Exception]): A callable that should return ``True``
+            if the given exception is retryable.
+        initial (float): The minimum a,out of time to delay in seconds. This
+            must be greater than 0.
+        maximum (float): The maximum amout of time to delay in seconds.
+        multiplier (float): The multiplier applied to the delay.
+        deadline (float): How long to keep retrying in seconds. The last sleep
+            period is shortened as necessary, so that the last retry runs at
+            ``deadline`` (and not considerably beyond it).
+        on_error (Callable[Exception]): A function to call while processing
+            a retryable exception. Any error raised by this function will
+            *not* be caught.
+    """
+
+    def __init__(
+        self,
+        predicate=if_transient_error,
+        initial=_DEFAULT_INITIAL_DELAY,
+        maximum=_DEFAULT_MAXIMUM_DELAY,
+        multiplier=_DEFAULT_DELAY_MULTIPLIER,
+        deadline=_DEFAULT_DEADLINE,
+        on_error=None,
+    ):
+        self._predicate = predicate
+        self._initial = initial
+        self._multiplier = multiplier
+        self._maximum = maximum
+        self._deadline = deadline
+        self._on_error = on_error
+
+    def __call__(self, func, on_error=None):
+        """Wrap a callable with retry behavior.
+
+        Args:
+            func (Callable): The callable to add retry behavior to.
+            on_error (Callable[Exception]): A function to call while processing
+                a retryable exception. Any error raised by this function will
+                *not* be caught.
+
+        Returns:
+            Callable: A callable that will invoke ``func`` with retry
+                behavior.
+        """
+        if self._on_error is not None:
+            on_error = self._on_error
+
+        @functools.wraps(func)
+        async def retry_wrapped_func(*args, **kwargs):
+            """A wrapper that calls target function with retry."""
+            target = functools.partial(func, *args, **kwargs)
+            sleep_generator = exponential_sleep_generator(
+                self._initial, self._maximum, multiplier=self._multiplier
+            )
+            return await retry_target(
+                target,
+                self._predicate,
+                sleep_generator,
+                self._deadline,
+                on_error=on_error,
+            )
+
+        return retry_wrapped_func
+
+    def _replace(
+        self,
+        predicate=None,
+        initial=None,
+        maximum=None,
+        multiplier=None,
+        deadline=None,
+        on_error=None,
+    ):
+        return AsyncRetry(
+            predicate=predicate or self._predicate,
+            initial=initial or self._initial,
+            maximum=maximum or self._maximum,
+            multiplier=multiplier or self._multiplier,
+            deadline=deadline or self._deadline,
+            on_error=on_error or self._on_error,
+        )
+
+    def with_deadline(self, deadline):
+        """Return a copy of this retry with the given deadline.
+
+        Args:
+            deadline (float): How long to keep retrying.
+
+        Returns:
+            AsyncRetry: A new retry instance with the given deadline.
+        """
+        return self._replace(deadline=deadline)
+
+    def with_predicate(self, predicate):
+        """Return a copy of this retry with the given predicate.
+
+        Args:
+            predicate (Callable[Exception]): A callable that should return
+                ``True`` if the given exception is retryable.
+
+        Returns:
+            AsyncRetry: A new retry instance with the given predicate.
+        """
+        return self._replace(predicate=predicate)
+
+    def with_delay(self, initial=None, maximum=None, multiplier=None):
+        """Return a copy of this retry with the given delay options.
+
+        Args:
+            initial (float): The minimum amout of time to delay. This must
+                be greater than 0.
+            maximum (float): The maximum amout of time to delay.
+            multiplier (float): The multiplier applied to the delay.
+
+        Returns:
+            AsyncRetry: A new retry instance with the given predicate.
+        """
+        return self._replace(initial=initial, maximum=maximum, multiplier=multiplier)
+
+    def __str__(self):
+        return (
+            "<AsyncRetry predicate={}, initial={:.1f}, maximum={:.1f}, "
+            "multiplier={:.1f}, deadline={:.1f}, on_error={}>".format(
+                self._predicate,
+                self._initial,
+                self._maximum,
+                self._multiplier,
+                self._deadline,
+                self._on_error,
+            )
+        )
diff --git a/google/api_core/timeout.py b/google/api_core/timeout.py
new file mode 100644
index 0000000..7323218
--- /dev/null
+++ b/google/api_core/timeout.py
@@ -0,0 +1,220 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Decorators for applying timeout arguments to functions.
+
+These decorators are used to wrap API methods to apply either a constant
+or exponential timeout argument.
+
+For example, imagine an API method that can take a while to return results,
+such as one that might block until a resource is ready:
+
+.. code-block:: python
+
+    def is_thing_ready(timeout=None):
+        response = requests.get('https://example.com/is_thing_ready')
+        response.raise_for_status()
+        return response.json()
+
+This module allows a function like this to be wrapped so that timeouts are
+automatically determined, for example:
+
+.. code-block:: python
+
+    timeout_ = timeout.ExponentialTimeout()
+    is_thing_ready_with_timeout = timeout_(is_thing_ready)
+
+    for n in range(10):
+        try:
+            is_thing_ready_with_timeout({'example': 'data'})
+        except:
+            pass
+
+In this example the first call to ``is_thing_ready`` will have a relatively
+small timeout (like 1 second). If the resource is available and the request
+completes quickly, the loop exits. But, if the resource isn't yet available
+and the request times out, it'll be retried - this time with a larger timeout.
+
+In the broader context these decorators are typically combined with
+:mod:`google.api_core.retry` to implement API methods with a signature that
+matches ``api_method(request, timeout=None, retry=None)``.
+"""
+
+from __future__ import unicode_literals
+
+import datetime
+import functools
+
+from google.api_core import datetime_helpers
+
+_DEFAULT_INITIAL_TIMEOUT = 5.0  # seconds
+_DEFAULT_MAXIMUM_TIMEOUT = 30.0  # seconds
+_DEFAULT_TIMEOUT_MULTIPLIER = 2.0
+# If specified, must be in seconds. If none, deadline is not used in the
+# timeout calculation.
+_DEFAULT_DEADLINE = None
+
+
+class ConstantTimeout(object):
+    """A decorator that adds a constant timeout argument.
+
+    This is effectively equivalent to
+    ``functools.partial(func, timeout=timeout)``.
+
+    Args:
+        timeout (Optional[float]): the timeout (in seconds) to applied to the
+            wrapped function. If `None`, the target function is expected to
+            never timeout.
+    """
+
+    def __init__(self, timeout=None):
+        self._timeout = timeout
+
+    def __call__(self, func):
+        """Apply the timeout decorator.
+
+        Args:
+            func (Callable): The function to apply the timeout argument to.
+                This function must accept a timeout keyword argument.
+
+        Returns:
+            Callable: The wrapped function.
+        """
+
+        @functools.wraps(func)
+        def func_with_timeout(*args, **kwargs):
+            """Wrapped function that adds timeout."""
+            kwargs["timeout"] = self._timeout
+            return func(*args, **kwargs)
+
+        return func_with_timeout
+
+    def __str__(self):
+        return "<ConstantTimeout timeout={:.1f}>".format(self._timeout)
+
+
+def _exponential_timeout_generator(initial, maximum, multiplier, deadline):
+    """A generator that yields exponential timeout values.
+
+    Args:
+        initial (float): The initial timeout.
+        maximum (float): The maximum timeout.
+        multiplier (float): The multiplier applied to the timeout.
+        deadline (float): The overall deadline across all invocations.
+
+    Yields:
+        float: A timeout value.
+    """
+    if deadline is not None:
+        deadline_datetime = datetime_helpers.utcnow() + datetime.timedelta(
+            seconds=deadline
+        )
+    else:
+        deadline_datetime = datetime.datetime.max
+
+    timeout = initial
+    while True:
+        now = datetime_helpers.utcnow()
+        yield min(
+            # The calculated timeout based on invocations.
+            timeout,
+            # The set maximum timeout.
+            maximum,
+            # The remaining time before the deadline is reached.
+            float((deadline_datetime - now).seconds),
+        )
+        timeout = timeout * multiplier
+
+
+class ExponentialTimeout(object):
+    """A decorator that adds an exponentially increasing timeout argument.
+
+    This is useful if a function is called multiple times. Each time the
+    function is called this decorator will calculate a new timeout parameter
+    based on the the number of times the function has been called.
+
+    For example
+
+    .. code-block:: python
+
+    Args:
+        initial (float): The initial timeout to pass.
+        maximum (float): The maximum timeout for any one call.
+        multiplier (float): The multiplier applied to the timeout for each
+            invocation.
+        deadline (Optional[float]): The overall deadline across all
+            invocations. This is used to prevent a very large calculated
+            timeout from pushing the overall execution time over the deadline.
+            This is especially useful in conjuction with
+            :mod:`google.api_core.retry`. If ``None``, the timeouts will not
+            be adjusted to accomodate an overall deadline.
+    """
+
+    def __init__(
+        self,
+        initial=_DEFAULT_INITIAL_TIMEOUT,
+        maximum=_DEFAULT_MAXIMUM_TIMEOUT,
+        multiplier=_DEFAULT_TIMEOUT_MULTIPLIER,
+        deadline=_DEFAULT_DEADLINE,
+    ):
+        self._initial = initial
+        self._maximum = maximum
+        self._multiplier = multiplier
+        self._deadline = deadline
+
+    def with_deadline(self, deadline):
+        """Return a copy of this teimout with the given deadline.
+
+        Args:
+            deadline (float): The overall deadline across all invocations.
+
+        Returns:
+            ExponentialTimeout: A new instance with the given deadline.
+        """
+        return ExponentialTimeout(
+            initial=self._initial,
+            maximum=self._maximum,
+            multiplier=self._multiplier,
+            deadline=deadline,
+        )
+
+    def __call__(self, func):
+        """Apply the timeout decorator.
+
+        Args:
+            func (Callable): The function to apply the timeout argument to.
+                This function must accept a timeout keyword argument.
+
+        Returns:
+            Callable: The wrapped function.
+        """
+        timeouts = _exponential_timeout_generator(
+            self._initial, self._maximum, self._multiplier, self._deadline
+        )
+
+        @functools.wraps(func)
+        def func_with_timeout(*args, **kwargs):
+            """Wrapped function that adds timeout."""
+            kwargs["timeout"] = next(timeouts)
+            return func(*args, **kwargs)
+
+        return func_with_timeout
+
+    def __str__(self):
+        return (
+            "<ExponentialTimeout initial={:.1f}, maximum={:.1f}, "
+            "multiplier={:.1f}, deadline={:.1f}>".format(
+                self._initial, self._maximum, self._multiplier, self._deadline
+            )
+        )
diff --git a/google/api_core/version.py b/google/api_core/version.py
new file mode 100644
index 0000000..999199f
--- /dev/null
+++ b/google/api_core/version.py
@@ -0,0 +1,15 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+__version__ = "2.3.0"
diff --git a/mypy.ini b/mypy.ini
new file mode 100644
index 0000000..5c11157
--- /dev/null
+++ b/mypy.ini
@@ -0,0 +1,4 @@
+[mypy]
+python_version = 3.6
+namespace_packages = True
+ignore_missing_imports = True
diff --git a/noxfile.py b/noxfile.py
new file mode 100644
index 0000000..db37c56
--- /dev/null
+++ b/noxfile.py
@@ -0,0 +1,245 @@
+# Copyright 2016 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import absolute_import
+import os
+import pathlib
+import shutil
+
+# https://github.com/google/importlab/issues/25
+import nox  # pytype: disable=import-error
+
+
+BLACK_VERSION = "black==19.10b0"
+BLACK_PATHS = ["docs", "google", "tests", "noxfile.py", "setup.py"]
+# Black and flake8 clash on the syntax for ignoring flake8's F401 in this file.
+BLACK_EXCLUDES = ["--exclude", "^/google/api_core/operations_v1/__init__.py"]
+
+DEFAULT_PYTHON_VERSION = "3.7"
+CURRENT_DIRECTORY = pathlib.Path(__file__).parent.absolute()
+
+# 'docfx' is excluded since it only needs to run in 'docs-presubmit'
+nox.options.sessions = [
+    "unit",
+    "unit_grpc_gcp",
+    "unit_wo_grpc",
+    "cover",
+    "pytype",
+    "mypy",
+    "lint",
+    "lint_setup_py",
+    "blacken",
+    "docs",
+]
+
+
+def _greater_or_equal_than_36(version_string):
+    tokens = version_string.split(".")
+    for i, token in enumerate(tokens):
+        try:
+            tokens[i] = int(token)
+        except ValueError:
+            pass
+    return tokens >= [3, 6]
+
+
+@nox.session(python=DEFAULT_PYTHON_VERSION)
+def lint(session):
+    """Run linters.
+
+    Returns a failure if the linters find linting errors or sufficiently
+    serious code quality issues.
+    """
+    session.install("flake8", "flake8-import-order", BLACK_VERSION)
+    session.install(".")
+    session.run(
+        "black", "--check", *BLACK_EXCLUDES, *BLACK_PATHS,
+    )
+    session.run("flake8", "google", "tests")
+
+
+@nox.session(python=DEFAULT_PYTHON_VERSION)
+def blacken(session):
+    """Run black.
+
+    Format code to uniform standard.
+    """
+    session.install(BLACK_VERSION)
+    session.run("black", *BLACK_EXCLUDES, *BLACK_PATHS)
+
+
+def default(session, install_grpc=True):
+    """Default unit test session.
+
+    This is intended to be run **without** an interpreter set, so
+    that the current ``python`` (on the ``PATH``) or the version of
+    Python corresponding to the ``nox`` binary the ``PATH`` can
+    run the tests.
+    """
+    constraints_path = str(
+        CURRENT_DIRECTORY / "testing" / f"constraints-{session.python}.txt"
+    )
+
+    # Install all test dependencies, then install this package in-place.
+    session.install("mock", "pytest", "pytest-cov")
+    if install_grpc:
+        session.install("-e", ".[grpc]", "-c", constraints_path)
+    else:
+        session.install("-e", ".", "-c", constraints_path)
+
+    pytest_args = [
+        "python",
+        "-m",
+        "py.test",
+        "--quiet",
+        "--cov=google.api_core",
+        "--cov=tests.unit",
+        "--cov-append",
+        "--cov-config=.coveragerc",
+        "--cov-report=",
+        "--cov-fail-under=0",
+        os.path.join("tests", "unit"),
+    ]
+    pytest_args.extend(session.posargs)
+
+    # Inject AsyncIO content and proto-plus, if version >= 3.6.
+    # proto-plus is needed for a field mask test in test_protobuf_helpers.py
+    if _greater_or_equal_than_36(session.python):
+        session.install("asyncmock", "pytest-asyncio", "proto-plus")
+
+        pytest_args.append("--cov=tests.asyncio")
+        pytest_args.append(os.path.join("tests", "asyncio"))
+        session.run(*pytest_args)
+    else:
+        # Run py.test against the unit tests.
+        session.run(*pytest_args)
+
+
+@nox.session(python=["3.6", "3.7", "3.8", "3.9", "3.10"])
+def unit(session):
+    """Run the unit test suite."""
+    default(session)
+
+
+@nox.session(python=["3.6", "3.7", "3.8", "3.9"])
+def unit_grpc_gcp(session):
+    """Run the unit test suite with grpcio-gcp installed."""
+    constraints_path = str(
+        CURRENT_DIRECTORY / "testing" / f"constraints-{session.python}.txt"
+    )
+    # Install grpcio-gcp
+    session.install("-e", ".[grpcgcp]", "-c", constraints_path)
+
+    default(session)
+
+
+@nox.session(python=["3.6", "3.10"])
+def unit_wo_grpc(session):
+    """Run the unit test suite w/o grpcio installed"""
+    default(session, install_grpc=False)
+
+
+@nox.session(python="3.6")
+def lint_setup_py(session):
+    """Verify that setup.py is valid (including RST check)."""
+
+    session.install("docutils", "Pygments")
+    session.run("python", "setup.py", "check", "--restructuredtext", "--strict")
+
+
+# No 3.7 because pytype supports up to 3.6 only.
+@nox.session(python="3.6")
+def pytype(session):
+    """Run type-checking."""
+    session.install(".[grpc, grpcgcp]", "pytype >= 2019.3.21")
+    session.run("pytype")
+
+
+@nox.session(python=DEFAULT_PYTHON_VERSION)
+def mypy(session):
+    """Run type-checking."""
+    session.install(".[grpc, grpcgcp]", "mypy")
+    session.install(
+        "types-setuptools", "types-requests", "types-protobuf", "types-mock"
+    )
+    session.run("mypy", "google", "tests")
+
+
+@nox.session(python="3.6")
+def cover(session):
+    """Run the final coverage report.
+
+    This outputs the coverage report aggregating coverage from the unit
+    test runs (not system test runs), and then erases coverage data.
+    """
+    session.install("coverage", "pytest-cov")
+    session.run("coverage", "report", "--show-missing", "--fail-under=100")
+    session.run("coverage", "erase")
+
+
+@nox.session(python="3.8")
+def docs(session):
+    """Build the docs for this library."""
+
+    session.install("-e", ".[grpc, grpcgcp]")
+    session.install("sphinx==4.0.1", "alabaster", "recommonmark")
+
+    shutil.rmtree(os.path.join("docs", "_build"), ignore_errors=True)
+    session.run(
+        "sphinx-build",
+        "-W",  # warnings as errors
+        "-T",  # show full traceback on exception
+        "-N",  # no colors
+        "-b",
+        "html",
+        "-d",
+        os.path.join("docs", "_build", "doctrees", ""),
+        os.path.join("docs", ""),
+        os.path.join("docs", "_build", "html", ""),
+    )
+
+
+@nox.session(python="3.8")
+def docfx(session):
+    """Build the docfx yaml files for this library."""
+
+    session.install("-e", ".")
+    session.install(
+        "sphinx==4.0.1", "alabaster", "recommonmark", "gcp-sphinx-docfx-yaml"
+    )
+
+    shutil.rmtree(os.path.join("docs", "_build"), ignore_errors=True)
+    session.run(
+        "sphinx-build",
+        "-T",  # show full traceback on exception
+        "-N",  # no colors
+        "-D",
+        (
+            "extensions=sphinx.ext.autodoc,"
+            "sphinx.ext.autosummary,"
+            "docfx_yaml.extension,"
+            "sphinx.ext.intersphinx,"
+            "sphinx.ext.coverage,"
+            "sphinx.ext.napoleon,"
+            "sphinx.ext.todo,"
+            "sphinx.ext.viewcode,"
+            "recommonmark"
+        ),
+        "-b",
+        "html",
+        "-d",
+        os.path.join("docs", "_build", "doctrees", ""),
+        os.path.join("docs", ""),
+        os.path.join("docs", "_build", "html", ""),
+    )
diff --git a/owlbot.py b/owlbot.py
new file mode 100644
index 0000000..451f7c4
--- /dev/null
+++ b/owlbot.py
@@ -0,0 +1,47 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""This script is used to synthesize generated parts of this library."""
+
+import synthtool as s
+from synthtool import gcp
+
+common = gcp.CommonTemplates()
+
+# ----------------------------------------------------------------------------
+# Add templated files
+# ----------------------------------------------------------------------------
+excludes = [
+    "noxfile.py",  # pytype
+    "setup.cfg",  # pytype
+    ".flake8",  # flake8-import-order, layout
+    ".coveragerc",  # layout
+    "CONTRIBUTING.rst",  # no systests
+]
+templated_files = common.py_library(microgenerator=True, cov_level=100)
+s.move(templated_files, excludes=excludes)
+
+# Add pytype support
+s.replace(
+    ".gitignore",
+    """\
+.pytest_cache
+""",
+    """\
+.pytest_cache
+.pytype
+""",
+)
+
+s.shell.run(["nox", "-s", "blacken"], hide_output=False)
diff --git a/renovate.json b/renovate.json
new file mode 100644
index 0000000..c21036d
--- /dev/null
+++ b/renovate.json
@@ -0,0 +1,12 @@
+{
+  "extends": [
+    "config:base",
+    "group:all",
+    ":preserveSemverRanges",
+    ":disableDependencyDashboard"
+  ],
+  "ignorePaths": [".pre-commit-config.yaml"],
+  "pip_requirements": {
+    "fileMatch": ["requirements-test.txt", "samples/[\\S/]*constraints.txt", "samples/[\\S/]*constraints-test.txt"]
+  }
+}
diff --git a/scripts/decrypt-secrets.sh b/scripts/decrypt-secrets.sh
new file mode 100755
index 0000000..21f6d2a
--- /dev/null
+++ b/scripts/decrypt-secrets.sh
@@ -0,0 +1,46 @@
+#!/bin/bash
+
+# Copyright 2015 Google Inc. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+DIR="$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
+ROOT=$( dirname "$DIR" )
+
+# Work from the project root.
+cd $ROOT
+
+# Prevent it from overriding files.
+# We recommend that sample authors use their own service account files and cloud project.
+# In that case, they are supposed to prepare these files by themselves.
+if [[ -f "testing/test-env.sh" ]] || \
+       [[ -f "testing/service-account.json" ]] || \
+       [[ -f "testing/client-secrets.json" ]]; then
+    echo "One or more target files exist, aborting."
+    exit 1
+fi
+
+# Use SECRET_MANAGER_PROJECT if set, fallback to cloud-devrel-kokoro-resources.
+PROJECT_ID="${SECRET_MANAGER_PROJECT:-cloud-devrel-kokoro-resources}"
+
+gcloud secrets versions access latest --secret="python-docs-samples-test-env" \
+       --project="${PROJECT_ID}" \
+       > testing/test-env.sh
+gcloud secrets versions access latest \
+       --secret="python-docs-samples-service-account" \
+       --project="${PROJECT_ID}" \
+       > testing/service-account.json
+gcloud secrets versions access latest \
+       --secret="python-docs-samples-client-secrets" \
+       --project="${PROJECT_ID}" \
+       > testing/client-secrets.json
diff --git a/scripts/readme-gen/readme_gen.py b/scripts/readme-gen/readme_gen.py
new file mode 100644
index 0000000..d309d6e
--- /dev/null
+++ b/scripts/readme-gen/readme_gen.py
@@ -0,0 +1,66 @@
+#!/usr/bin/env python
+
+# Copyright 2016 Google Inc
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+"""Generates READMEs using configuration defined in yaml."""
+
+import argparse
+import io
+import os
+import subprocess
+
+import jinja2
+import yaml
+
+
+jinja_env = jinja2.Environment(
+    trim_blocks=True,
+    loader=jinja2.FileSystemLoader(
+        os.path.abspath(os.path.join(os.path.dirname(__file__), 'templates'))))
+
+README_TMPL = jinja_env.get_template('README.tmpl.rst')
+
+
+def get_help(file):
+    return subprocess.check_output(['python', file, '--help']).decode()
+
+
+def main():
+    parser = argparse.ArgumentParser()
+    parser.add_argument('source')
+    parser.add_argument('--destination', default='README.rst')
+
+    args = parser.parse_args()
+
+    source = os.path.abspath(args.source)
+    root = os.path.dirname(source)
+    destination = os.path.join(root, args.destination)
+
+    jinja_env.globals['get_help'] = get_help
+
+    with io.open(source, 'r') as f:
+        config = yaml.load(f)
+
+    # This allows get_help to execute in the right directory.
+    os.chdir(root)
+
+    output = README_TMPL.render(config)
+
+    with io.open(destination, 'w') as f:
+        f.write(output)
+
+
+if __name__ == '__main__':
+    main()
diff --git a/scripts/readme-gen/templates/README.tmpl.rst b/scripts/readme-gen/templates/README.tmpl.rst
new file mode 100644
index 0000000..4fd2397
--- /dev/null
+++ b/scripts/readme-gen/templates/README.tmpl.rst
@@ -0,0 +1,87 @@
+{# The following line is a lie. BUT! Once jinja2 is done with it, it will
+    become truth! #}
+.. This file is automatically generated. Do not edit this file directly.
+
+{{product.name}} Python Samples
+===============================================================================
+
+.. image:: https://gstatic.com/cloudssh/images/open-btn.png
+   :target: https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/GoogleCloudPlatform/python-docs-samples&page=editor&open_in_editor={{folder}}/README.rst
+
+
+This directory contains samples for {{product.name}}. {{product.description}}
+
+{{description}}
+
+.. _{{product.name}}: {{product.url}}
+
+{% if required_api_url %}
+To run the sample, you need to enable the API at: {{required_api_url}}
+{% endif %}
+
+{% if required_role %}
+To run the sample, you need to have `{{required_role}}` role.
+{% endif %}
+
+{{other_required_steps}}
+
+{% if setup %}
+Setup
+-------------------------------------------------------------------------------
+
+{% for section in setup %}
+
+{% include section + '.tmpl.rst' %}
+
+{% endfor %}
+{% endif %}
+
+{% if samples %}
+Samples
+-------------------------------------------------------------------------------
+
+{% for sample in samples %}
+{{sample.name}}
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+{% if not sample.hide_cloudshell_button %}
+.. image:: https://gstatic.com/cloudssh/images/open-btn.png
+   :target: https://console.cloud.google.com/cloudshell/open?git_repo=https://github.com/GoogleCloudPlatform/python-docs-samples&page=editor&open_in_editor={{folder}}/{{sample.file}},{{folder}}/README.rst
+{% endif %}
+
+
+{{sample.description}}
+
+To run this sample:
+
+.. code-block:: bash
+
+    $ python {{sample.file}}
+{% if sample.show_help %}
+
+    {{get_help(sample.file)|indent}}
+{% endif %}
+
+
+{% endfor %}
+{% endif %}
+
+{% if cloud_client_library %}
+
+The client library
+-------------------------------------------------------------------------------
+
+This sample uses the `Google Cloud Client Library for Python`_.
+You can read the documentation for more details on API usage and use GitHub
+to `browse the source`_ and  `report issues`_.
+
+.. _Google Cloud Client Library for Python:
+    https://googlecloudplatform.github.io/google-cloud-python/
+.. _browse the source:
+    https://github.com/GoogleCloudPlatform/google-cloud-python
+.. _report issues:
+    https://github.com/GoogleCloudPlatform/google-cloud-python/issues
+
+{% endif %}
+
+.. _Google Cloud SDK: https://cloud.google.com/sdk/
\ No newline at end of file
diff --git a/scripts/readme-gen/templates/auth.tmpl.rst b/scripts/readme-gen/templates/auth.tmpl.rst
new file mode 100644
index 0000000..1446b94
--- /dev/null
+++ b/scripts/readme-gen/templates/auth.tmpl.rst
@@ -0,0 +1,9 @@
+Authentication
+++++++++++++++
+
+This sample requires you to have authentication setup. Refer to the
+`Authentication Getting Started Guide`_ for instructions on setting up
+credentials for applications.
+
+.. _Authentication Getting Started Guide:
+    https://cloud.google.com/docs/authentication/getting-started
diff --git a/scripts/readme-gen/templates/auth_api_key.tmpl.rst b/scripts/readme-gen/templates/auth_api_key.tmpl.rst
new file mode 100644
index 0000000..11957ce
--- /dev/null
+++ b/scripts/readme-gen/templates/auth_api_key.tmpl.rst
@@ -0,0 +1,14 @@
+Authentication
+++++++++++++++
+
+Authentication for this service is done via an `API Key`_. To obtain an API
+Key:
+
+1. Open the `Cloud Platform Console`_
+2. Make sure that billing is enabled for your project.
+3. From the **Credentials** page, create a new **API Key** or use an existing
+   one for your project.
+
+.. _API Key:
+    https://developers.google.com/api-client-library/python/guide/aaa_apikeys
+.. _Cloud Console: https://console.cloud.google.com/project?_
diff --git a/scripts/readme-gen/templates/install_deps.tmpl.rst b/scripts/readme-gen/templates/install_deps.tmpl.rst
new file mode 100644
index 0000000..275d649
--- /dev/null
+++ b/scripts/readme-gen/templates/install_deps.tmpl.rst
@@ -0,0 +1,29 @@
+Install Dependencies
+++++++++++++++++++++
+
+#. Clone python-docs-samples and change directory to the sample directory you want to use.
+
+    .. code-block:: bash
+
+        $ git clone https://github.com/GoogleCloudPlatform/python-docs-samples.git
+
+#. Install `pip`_ and `virtualenv`_ if you do not already have them. You may want to refer to the `Python Development Environment Setup Guide`_ for Google Cloud Platform for instructions.
+
+   .. _Python Development Environment Setup Guide:
+       https://cloud.google.com/python/setup
+
+#. Create a virtualenv. Samples are compatible with Python 3.6+.
+
+    .. code-block:: bash
+
+        $ virtualenv env
+        $ source env/bin/activate
+
+#. Install the dependencies needed to run the samples.
+
+    .. code-block:: bash
+
+        $ pip install -r requirements.txt
+
+.. _pip: https://pip.pypa.io/
+.. _virtualenv: https://virtualenv.pypa.io/
diff --git a/scripts/readme-gen/templates/install_portaudio.tmpl.rst b/scripts/readme-gen/templates/install_portaudio.tmpl.rst
new file mode 100644
index 0000000..5ea33d1
--- /dev/null
+++ b/scripts/readme-gen/templates/install_portaudio.tmpl.rst
@@ -0,0 +1,35 @@
+Install PortAudio
++++++++++++++++++
+
+Install `PortAudio`_. This is required by the `PyAudio`_ library to stream
+audio from your computer's microphone. PyAudio depends on PortAudio for cross-platform compatibility, and is installed differently depending on the
+platform.
+
+* For Mac OS X, you can use `Homebrew`_::
+
+      brew install portaudio
+
+  **Note**: if you encounter an error when running `pip install` that indicates
+  it can't find `portaudio.h`, try running `pip install` with the following
+  flags::
+
+      pip install --global-option='build_ext' \
+          --global-option='-I/usr/local/include' \
+          --global-option='-L/usr/local/lib' \
+          pyaudio
+
+* For Debian / Ubuntu Linux::
+
+      apt-get install portaudio19-dev python-all-dev
+
+* Windows may work without having to install PortAudio explicitly (it will get
+  installed with PyAudio).
+
+For more details, see the `PyAudio installation`_ page.
+
+
+.. _PyAudio: https://people.csail.mit.edu/hubert/pyaudio/
+.. _PortAudio: http://www.portaudio.com/
+.. _PyAudio installation:
+  https://people.csail.mit.edu/hubert/pyaudio/#downloads
+.. _Homebrew: http://brew.sh
diff --git a/setup.cfg b/setup.cfg
new file mode 100644
index 0000000..0be0b3f
--- /dev/null
+++ b/setup.cfg
@@ -0,0 +1,12 @@
+[bdist_wheel]
+universal = 1
+
+[pytype]
+python_version = 3.6
+inputs =
+    google/
+exclude =
+    tests/
+output = .pytype/
+# Workaround for https://github.com/google/pytype/issues/150
+disable = pyi-error
diff --git a/setup.py b/setup.py
new file mode 100644
index 0000000..ddc5600
--- /dev/null
+++ b/setup.py
@@ -0,0 +1,102 @@
+# Copyright 2018 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import io
+import os
+
+import setuptools
+
+
+# Package metadata.
+
+name = "google-api-core"
+description = "Google API client core library"
+
+# Should be one of:
+# 'Development Status :: 3 - Alpha'
+# 'Development Status :: 4 - Beta'
+# 'Development Status :: 5 - Production/Stable'
+release_status = "Development Status :: 5 - Production/Stable"
+dependencies = [
+    "googleapis-common-protos >= 1.52.0, < 2.0dev",
+    "protobuf >= 3.12.0",
+    "google-auth >= 1.25.0, < 3.0dev",
+    "requests >= 2.18.0, < 3.0.0dev",
+    "setuptools >= 40.3.0",
+]
+extras = {
+    "grpc": ["grpcio >= 1.33.2, < 2.0dev", "grpcio-status >= 1.33.2, < 2.0dev"],
+    "grpcgcp": "grpcio-gcp >= 0.2.2",
+    "grpcio-gcp": "grpcio-gcp >= 0.2.2",
+}
+
+
+# Setup boilerplate below this line.
+
+package_root = os.path.abspath(os.path.dirname(__file__))
+
+
+version = {}
+with open(os.path.join(package_root, "google/api_core/version.py")) as fp:
+    exec(fp.read(), version)
+version = version["__version__"]
+
+readme_filename = os.path.join(package_root, "README.rst")
+with io.open(readme_filename, encoding="utf-8") as readme_file:
+    readme = readme_file.read()
+
+# Only include packages under the 'google' namespace. Do not include tests,
+# benchmarks, etc.
+packages = [
+    package for package in setuptools.find_packages() if package.startswith("google")
+]
+
+# Determine which namespaces are needed.
+namespaces = ["google"]
+if "google.cloud" in packages:
+    namespaces.append("google.cloud")
+
+
+setuptools.setup(
+    name=name,
+    version=version,
+    description=description,
+    long_description=readme,
+    author="Google LLC",
+    author_email="googleapis-packages@google.com",
+    license="Apache 2.0",
+    url="https://github.com/googleapis/python-api-core",
+    classifiers=[
+        release_status,
+        "Intended Audience :: Developers",
+        "License :: OSI Approved :: Apache Software License",
+        "Programming Language :: Python",
+        "Programming Language :: Python :: 3",
+        "Programming Language :: Python :: 3.6",
+        "Programming Language :: Python :: 3.7",
+        "Programming Language :: Python :: 3.8",
+        "Programming Language :: Python :: 3.9",
+        "Programming Language :: Python :: 3.10",
+        "Operating System :: OS Independent",
+        "Topic :: Internet",
+    ],
+    platforms="Posix; MacOS X; Windows",
+    packages=packages,
+    namespace_packages=namespaces,
+    install_requires=dependencies,
+    extras_require=extras,
+    python_requires=">=3.6",
+    include_package_data=True,
+    zip_safe=False,
+)
diff --git a/testing/.gitignore b/testing/.gitignore
new file mode 100644
index 0000000..b05fbd6
--- /dev/null
+++ b/testing/.gitignore
@@ -0,0 +1,3 @@
+test-env.sh
+service-account.json
+client-secrets.json
\ No newline at end of file
diff --git a/testing/constraints-3.10.txt b/testing/constraints-3.10.txt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/testing/constraints-3.10.txt
diff --git a/testing/constraints-3.11.txt b/testing/constraints-3.11.txt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/testing/constraints-3.11.txt
diff --git a/testing/constraints-3.6.txt b/testing/constraints-3.6.txt
new file mode 100644
index 0000000..0c2a07b
--- /dev/null
+++ b/testing/constraints-3.6.txt
@@ -0,0 +1,17 @@
+# This constraints file is used to check that lower bounds
+# are correct in setup.py
+# List *all* library dependencies and extras in this file.
+# Pin the version to the lower bound.
+#
+# e.g., if setup.py has "foo >= 1.14.0, < 2.0.0dev",
+# Then this file should have foo==1.14.0
+googleapis-common-protos==1.52.0
+protobuf==3.12.0
+google-auth==1.25.0
+requests==2.18.0
+setuptools==40.3.0
+packaging==14.3
+grpcio==1.33.2
+grpcio-gcp==0.2.2
+grpcio-gcp==0.2.2
+grpcio-status==1.33.2
diff --git a/testing/constraints-3.7.txt b/testing/constraints-3.7.txt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/testing/constraints-3.7.txt
diff --git a/testing/constraints-3.8.txt b/testing/constraints-3.8.txt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/testing/constraints-3.8.txt
diff --git a/testing/constraints-3.9.txt b/testing/constraints-3.9.txt
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/testing/constraints-3.9.txt
diff --git a/tests/__init__.py b/tests/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/__init__.py
diff --git a/tests/asyncio/__init__.py b/tests/asyncio/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/asyncio/__init__.py
diff --git a/tests/asyncio/future/__init__.py b/tests/asyncio/future/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/asyncio/future/__init__.py
diff --git a/tests/asyncio/future/test_async_future.py b/tests/asyncio/future/test_async_future.py
new file mode 100644
index 0000000..1e9ae33
--- /dev/null
+++ b/tests/asyncio/future/test_async_future.py
@@ -0,0 +1,228 @@
+# Copyright 2017, Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import asyncio
+
+import mock
+import pytest
+
+from google.api_core import exceptions
+from google.api_core.future import async_future
+
+
+class AsyncFuture(async_future.AsyncFuture):
+    async def done(self):
+        return False
+
+    async def cancel(self):
+        return True
+
+    async def cancelled(self):
+        return False
+
+    async def running(self):
+        return True
+
+
+@pytest.mark.asyncio
+async def test_polling_future_constructor():
+    future = AsyncFuture()
+    assert not await future.done()
+    assert not await future.cancelled()
+    assert await future.running()
+    assert await future.cancel()
+
+
+@pytest.mark.asyncio
+async def test_set_result():
+    future = AsyncFuture()
+    callback = mock.Mock()
+
+    future.set_result(1)
+
+    assert await future.result() == 1
+    callback_called = asyncio.Event()
+
+    def callback(unused_future):
+        callback_called.set()
+
+    future.add_done_callback(callback)
+    await callback_called.wait()
+
+
+@pytest.mark.asyncio
+async def test_set_exception():
+    future = AsyncFuture()
+    exception = ValueError("meep")
+
+    future.set_exception(exception)
+
+    assert await future.exception() == exception
+    with pytest.raises(ValueError):
+        await future.result()
+
+    callback_called = asyncio.Event()
+
+    def callback(unused_future):
+        callback_called.set()
+
+    future.add_done_callback(callback)
+    await callback_called.wait()
+
+
+@pytest.mark.asyncio
+async def test_invoke_callback_exception():
+    future = AsyncFuture()
+    future.set_result(42)
+
+    # This should not raise, despite the callback causing an exception.
+    callback_called = asyncio.Event()
+
+    def callback(unused_future):
+        callback_called.set()
+        raise ValueError()
+
+    future.add_done_callback(callback)
+    await callback_called.wait()
+
+
+class AsyncFutureWithPoll(AsyncFuture):
+    def __init__(self):
+        super().__init__()
+        self.poll_count = 0
+        self.event = asyncio.Event()
+
+    async def done(self):
+        self.poll_count += 1
+        await self.event.wait()
+        self.set_result(42)
+        return True
+
+
+@pytest.mark.asyncio
+async def test_result_with_polling():
+    future = AsyncFutureWithPoll()
+
+    future.event.set()
+    result = await future.result()
+
+    assert result == 42
+    assert future.poll_count == 1
+    # Repeated calls should not cause additional polling
+    assert await future.result() == result
+    assert future.poll_count == 1
+
+
+class AsyncFutureTimeout(AsyncFutureWithPoll):
+    async def done(self):
+        await asyncio.sleep(0.2)
+        return False
+
+
+@pytest.mark.asyncio
+async def test_result_timeout():
+    future = AsyncFutureTimeout()
+    with pytest.raises(asyncio.TimeoutError):
+        await future.result(timeout=0.2)
+
+
+@pytest.mark.asyncio
+async def test_exception_timeout():
+    future = AsyncFutureTimeout()
+    with pytest.raises(asyncio.TimeoutError):
+        await future.exception(timeout=0.2)
+
+
+@pytest.mark.asyncio
+async def test_result_timeout_with_retry():
+    future = AsyncFutureTimeout()
+    with pytest.raises(asyncio.TimeoutError):
+        await future.exception(timeout=0.4)
+
+
+class AsyncFutureTransient(AsyncFutureWithPoll):
+    def __init__(self, errors):
+        super().__init__()
+        self._errors = errors
+
+    async def done(self):
+        if self._errors:
+            error, self._errors = self._errors[0], self._errors[1:]
+            raise error("testing")
+        self.poll_count += 1
+        self.set_result(42)
+        return True
+
+
+@mock.patch("asyncio.sleep", autospec=True)
+@pytest.mark.asyncio
+async def test_result_transient_error(unused_sleep):
+    future = AsyncFutureTransient(
+        (
+            exceptions.TooManyRequests,
+            exceptions.InternalServerError,
+            exceptions.BadGateway,
+        )
+    )
+    result = await future.result()
+    assert result == 42
+    assert future.poll_count == 1
+    # Repeated calls should not cause additional polling
+    assert await future.result() == result
+    assert future.poll_count == 1
+
+
+@pytest.mark.asyncio
+async def test_callback_concurrency():
+    future = AsyncFutureWithPoll()
+
+    callback_called = asyncio.Event()
+
+    def callback(unused_future):
+        callback_called.set()
+
+    future.add_done_callback(callback)
+
+    # Give the thread a second to poll
+    await asyncio.sleep(1)
+    assert future.poll_count == 1
+
+    future.event.set()
+    await callback_called.wait()
+
+
+@pytest.mark.asyncio
+async def test_double_callback_concurrency():
+    future = AsyncFutureWithPoll()
+
+    callback_called = asyncio.Event()
+
+    def callback(unused_future):
+        callback_called.set()
+
+    callback_called2 = asyncio.Event()
+
+    def callback2(unused_future):
+        callback_called2.set()
+
+    future.add_done_callback(callback)
+    future.add_done_callback(callback2)
+
+    # Give the thread a second to poll
+    await asyncio.sleep(1)
+    future.event.set()
+
+    assert future.poll_count == 1
+    await callback_called.wait()
+    await callback_called2.wait()
diff --git a/tests/asyncio/gapic/test_config_async.py b/tests/asyncio/gapic/test_config_async.py
new file mode 100644
index 0000000..dbb05d5
--- /dev/null
+++ b/tests/asyncio/gapic/test_config_async.py
@@ -0,0 +1,95 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import pytest
+
+try:
+    import grpc  # noqa: F401
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+from google.api_core import exceptions
+from google.api_core.gapic_v1 import config_async
+
+
+INTERFACE_CONFIG = {
+    "retry_codes": {
+        "idempotent": ["DEADLINE_EXCEEDED", "UNAVAILABLE"],
+        "other": ["FAILED_PRECONDITION"],
+        "non_idempotent": [],
+    },
+    "retry_params": {
+        "default": {
+            "initial_retry_delay_millis": 1000,
+            "retry_delay_multiplier": 2.5,
+            "max_retry_delay_millis": 120000,
+            "initial_rpc_timeout_millis": 120000,
+            "rpc_timeout_multiplier": 1.0,
+            "max_rpc_timeout_millis": 120000,
+            "total_timeout_millis": 600000,
+        },
+        "other": {
+            "initial_retry_delay_millis": 1000,
+            "retry_delay_multiplier": 1,
+            "max_retry_delay_millis": 1000,
+            "initial_rpc_timeout_millis": 1000,
+            "rpc_timeout_multiplier": 1,
+            "max_rpc_timeout_millis": 1000,
+            "total_timeout_millis": 1000,
+        },
+    },
+    "methods": {
+        "AnnotateVideo": {
+            "timeout_millis": 60000,
+            "retry_codes_name": "idempotent",
+            "retry_params_name": "default",
+        },
+        "Other": {
+            "timeout_millis": 60000,
+            "retry_codes_name": "other",
+            "retry_params_name": "other",
+        },
+        "Plain": {"timeout_millis": 30000},
+    },
+}
+
+
+def test_create_method_configs():
+    method_configs = config_async.parse_method_configs(INTERFACE_CONFIG)
+
+    retry, timeout = method_configs["AnnotateVideo"]
+    assert retry._predicate(exceptions.DeadlineExceeded(None))
+    assert retry._predicate(exceptions.ServiceUnavailable(None))
+    assert retry._initial == 1.0
+    assert retry._multiplier == 2.5
+    assert retry._maximum == 120.0
+    assert retry._deadline == 600.0
+    assert timeout._initial == 120.0
+    assert timeout._multiplier == 1.0
+    assert timeout._maximum == 120.0
+
+    retry, timeout = method_configs["Other"]
+    assert retry._predicate(exceptions.FailedPrecondition(None))
+    assert retry._initial == 1.0
+    assert retry._multiplier == 1.0
+    assert retry._maximum == 1.0
+    assert retry._deadline == 1.0
+    assert timeout._initial == 1.0
+    assert timeout._multiplier == 1.0
+    assert timeout._maximum == 1.0
+
+    retry, timeout = method_configs["Plain"]
+    assert retry is None
+    assert timeout._timeout == 30.0
diff --git a/tests/asyncio/gapic/test_method_async.py b/tests/asyncio/gapic/test_method_async.py
new file mode 100644
index 0000000..1410747
--- /dev/null
+++ b/tests/asyncio/gapic/test_method_async.py
@@ -0,0 +1,248 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import datetime
+
+import mock
+import pytest
+
+try:
+    from grpc import aio
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+from google.api_core import exceptions
+from google.api_core import gapic_v1
+from google.api_core import grpc_helpers_async
+from google.api_core import retry_async
+from google.api_core import timeout
+
+
+def _utcnow_monotonic():
+    current_time = datetime.datetime.min
+    delta = datetime.timedelta(seconds=0.5)
+    while True:
+        yield current_time
+        current_time += delta
+
+
+@pytest.mark.asyncio
+async def test_wrap_method_basic():
+    fake_call = grpc_helpers_async.FakeUnaryUnaryCall(42)
+    method = mock.Mock(spec=aio.UnaryUnaryMultiCallable, return_value=fake_call)
+
+    wrapped_method = gapic_v1.method_async.wrap_method(method)
+
+    result = await wrapped_method(1, 2, meep="moop")
+
+    assert result == 42
+    method.assert_called_once_with(1, 2, meep="moop", metadata=mock.ANY)
+
+    # Check that the default client info was specified in the metadata.
+    metadata = method.call_args[1]["metadata"]
+    assert len(metadata) == 1
+    client_info = gapic_v1.client_info.DEFAULT_CLIENT_INFO
+    user_agent_metadata = client_info.to_grpc_metadata()
+    assert user_agent_metadata in metadata
+
+
+@pytest.mark.asyncio
+async def test_wrap_method_with_no_client_info():
+    fake_call = grpc_helpers_async.FakeUnaryUnaryCall()
+    method = mock.Mock(spec=aio.UnaryUnaryMultiCallable, return_value=fake_call)
+
+    wrapped_method = gapic_v1.method_async.wrap_method(method, client_info=None)
+
+    await wrapped_method(1, 2, meep="moop")
+
+    method.assert_called_once_with(1, 2, meep="moop")
+
+
+@pytest.mark.asyncio
+async def test_wrap_method_with_custom_client_info():
+    client_info = gapic_v1.client_info.ClientInfo(
+        python_version=1,
+        grpc_version=2,
+        api_core_version=3,
+        gapic_version=4,
+        client_library_version=5,
+    )
+    fake_call = grpc_helpers_async.FakeUnaryUnaryCall()
+    method = mock.Mock(spec=aio.UnaryUnaryMultiCallable, return_value=fake_call)
+
+    wrapped_method = gapic_v1.method_async.wrap_method(method, client_info=client_info)
+
+    await wrapped_method(1, 2, meep="moop")
+
+    method.assert_called_once_with(1, 2, meep="moop", metadata=mock.ANY)
+
+    # Check that the custom client info was specified in the metadata.
+    metadata = method.call_args[1]["metadata"]
+    assert client_info.to_grpc_metadata() in metadata
+
+
+@pytest.mark.asyncio
+async def test_invoke_wrapped_method_with_metadata():
+    fake_call = grpc_helpers_async.FakeUnaryUnaryCall()
+    method = mock.Mock(spec=aio.UnaryUnaryMultiCallable, return_value=fake_call)
+
+    wrapped_method = gapic_v1.method_async.wrap_method(method)
+
+    await wrapped_method(mock.sentinel.request, metadata=[("a", "b")])
+
+    method.assert_called_once_with(mock.sentinel.request, metadata=mock.ANY)
+    metadata = method.call_args[1]["metadata"]
+    # Metadata should have two items: the client info metadata and our custom
+    # metadata.
+    assert len(metadata) == 2
+    assert ("a", "b") in metadata
+
+
+@pytest.mark.asyncio
+async def test_invoke_wrapped_method_with_metadata_as_none():
+    fake_call = grpc_helpers_async.FakeUnaryUnaryCall()
+    method = mock.Mock(spec=aio.UnaryUnaryMultiCallable, return_value=fake_call)
+
+    wrapped_method = gapic_v1.method_async.wrap_method(method)
+
+    await wrapped_method(mock.sentinel.request, metadata=None)
+
+    method.assert_called_once_with(mock.sentinel.request, metadata=mock.ANY)
+    metadata = method.call_args[1]["metadata"]
+    # Metadata should have just one items: the client info metadata.
+    assert len(metadata) == 1
+
+
+@mock.patch("asyncio.sleep")
+@pytest.mark.asyncio
+async def test_wrap_method_with_default_retry_and_timeout(unused_sleep):
+    fake_call = grpc_helpers_async.FakeUnaryUnaryCall(42)
+    method = mock.Mock(
+        spec=aio.UnaryUnaryMultiCallable,
+        side_effect=[exceptions.InternalServerError(None), fake_call],
+    )
+
+    default_retry = retry_async.AsyncRetry()
+    default_timeout = timeout.ConstantTimeout(60)
+    wrapped_method = gapic_v1.method_async.wrap_method(
+        method, default_retry, default_timeout
+    )
+
+    result = await wrapped_method()
+
+    assert result == 42
+    assert method.call_count == 2
+    method.assert_called_with(timeout=60, metadata=mock.ANY)
+
+
+@mock.patch("asyncio.sleep")
+@pytest.mark.asyncio
+async def test_wrap_method_with_default_retry_and_timeout_using_sentinel(unused_sleep):
+    fake_call = grpc_helpers_async.FakeUnaryUnaryCall(42)
+    method = mock.Mock(
+        spec=aio.UnaryUnaryMultiCallable,
+        side_effect=[exceptions.InternalServerError(None), fake_call],
+    )
+
+    default_retry = retry_async.AsyncRetry()
+    default_timeout = timeout.ConstantTimeout(60)
+    wrapped_method = gapic_v1.method_async.wrap_method(
+        method, default_retry, default_timeout
+    )
+
+    result = await wrapped_method(
+        retry=gapic_v1.method_async.DEFAULT, timeout=gapic_v1.method_async.DEFAULT,
+    )
+
+    assert result == 42
+    assert method.call_count == 2
+    method.assert_called_with(timeout=60, metadata=mock.ANY)
+
+
+@mock.patch("asyncio.sleep")
+@pytest.mark.asyncio
+async def test_wrap_method_with_overriding_retry_and_timeout(unused_sleep):
+    fake_call = grpc_helpers_async.FakeUnaryUnaryCall(42)
+    method = mock.Mock(
+        spec=aio.UnaryUnaryMultiCallable,
+        side_effect=[exceptions.NotFound(None), fake_call],
+    )
+
+    default_retry = retry_async.AsyncRetry()
+    default_timeout = timeout.ConstantTimeout(60)
+    wrapped_method = gapic_v1.method_async.wrap_method(
+        method, default_retry, default_timeout
+    )
+
+    result = await wrapped_method(
+        retry=retry_async.AsyncRetry(
+            retry_async.if_exception_type(exceptions.NotFound)
+        ),
+        timeout=timeout.ConstantTimeout(22),
+    )
+
+    assert result == 42
+    assert method.call_count == 2
+    method.assert_called_with(timeout=22, metadata=mock.ANY)
+
+
+@mock.patch("asyncio.sleep")
+@mock.patch(
+    "google.api_core.datetime_helpers.utcnow",
+    side_effect=_utcnow_monotonic(),
+    autospec=True,
+)
+@pytest.mark.asyncio
+async def test_wrap_method_with_overriding_retry_deadline(utcnow, unused_sleep):
+    fake_call = grpc_helpers_async.FakeUnaryUnaryCall(42)
+    method = mock.Mock(
+        spec=aio.UnaryUnaryMultiCallable,
+        side_effect=([exceptions.InternalServerError(None)] * 4) + [fake_call],
+    )
+
+    default_retry = retry_async.AsyncRetry()
+    default_timeout = timeout.ExponentialTimeout(deadline=60)
+    wrapped_method = gapic_v1.method_async.wrap_method(
+        method, default_retry, default_timeout
+    )
+
+    # Overriding only the retry's deadline should also override the timeout's
+    # deadline.
+    result = await wrapped_method(retry=default_retry.with_deadline(30))
+
+    assert result == 42
+    timeout_args = [call[1]["timeout"] for call in method.call_args_list]
+    assert timeout_args == [5.0, 10.0, 20.0, 26.0, 25.0]
+    assert utcnow.call_count == (
+        1
+        + 1  # Compute wait_for timeout in retry_async
+        + 5  # First to set the deadline.
+        + 5  # One for each min(timeout, maximum, (DEADLINE - NOW).seconds)
+    )
+
+
+@pytest.mark.asyncio
+async def test_wrap_method_with_overriding_timeout_as_a_number():
+    fake_call = grpc_helpers_async.FakeUnaryUnaryCall(42)
+    method = mock.Mock(spec=aio.UnaryUnaryMultiCallable, return_value=fake_call)
+    default_retry = retry_async.AsyncRetry()
+    default_timeout = timeout.ConstantTimeout(60)
+    wrapped_method = gapic_v1.method_async.wrap_method(
+        method, default_retry, default_timeout
+    )
+
+    result = await wrapped_method(timeout=22)
+
+    assert result == 42
+    method.assert_called_once_with(timeout=22, metadata=mock.ANY)
diff --git a/tests/asyncio/operations_v1/__init__.py b/tests/asyncio/operations_v1/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/asyncio/operations_v1/__init__.py
diff --git a/tests/asyncio/operations_v1/test_operations_async_client.py b/tests/asyncio/operations_v1/test_operations_async_client.py
new file mode 100644
index 0000000..47c3b4b
--- /dev/null
+++ b/tests/asyncio/operations_v1/test_operations_async_client.py
@@ -0,0 +1,113 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import mock
+import pytest
+
+try:
+    from grpc import aio
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+from google.api_core import grpc_helpers_async
+from google.api_core import operations_v1
+from google.api_core import page_iterator_async
+from google.longrunning import operations_pb2
+from google.protobuf import empty_pb2
+
+
+def _mock_grpc_objects(response):
+    fake_call = grpc_helpers_async.FakeUnaryUnaryCall(response)
+    method = mock.Mock(spec=aio.UnaryUnaryMultiCallable, return_value=fake_call)
+    mocked_channel = mock.Mock()
+    mocked_channel.unary_unary = mock.Mock(return_value=method)
+    return mocked_channel, method, fake_call
+
+
+@pytest.mark.asyncio
+async def test_get_operation():
+    mocked_channel, method, fake_call = _mock_grpc_objects(
+        operations_pb2.Operation(name="meep")
+    )
+    client = operations_v1.OperationsAsyncClient(mocked_channel)
+
+    response = await client.get_operation("name", metadata=[("header", "foo")])
+    assert method.call_count == 1
+    assert tuple(method.call_args_list[0])[0][0].name == "name"
+    assert ("header", "foo") in tuple(method.call_args_list[0])[1]["metadata"]
+    assert ("x-goog-request-params", "name=name") in tuple(method.call_args_list[0])[1][
+        "metadata"
+    ]
+    assert response == fake_call.response
+
+
+@pytest.mark.asyncio
+async def test_list_operations():
+    operations = [
+        operations_pb2.Operation(name="1"),
+        operations_pb2.Operation(name="2"),
+    ]
+    list_response = operations_pb2.ListOperationsResponse(operations=operations)
+
+    mocked_channel, method, fake_call = _mock_grpc_objects(list_response)
+    client = operations_v1.OperationsAsyncClient(mocked_channel)
+
+    pager = await client.list_operations("name", "filter", metadata=[("header", "foo")])
+
+    assert isinstance(pager, page_iterator_async.AsyncIterator)
+    responses = []
+    async for response in pager:
+        responses.append(response)
+
+    assert responses == operations
+
+    assert method.call_count == 1
+    assert ("header", "foo") in tuple(method.call_args_list[0])[1]["metadata"]
+    assert ("x-goog-request-params", "name=name") in tuple(method.call_args_list[0])[1][
+        "metadata"
+    ]
+    request = tuple(method.call_args_list[0])[0][0]
+    assert isinstance(request, operations_pb2.ListOperationsRequest)
+    assert request.name == "name"
+    assert request.filter == "filter"
+
+
+@pytest.mark.asyncio
+async def test_delete_operation():
+    mocked_channel, method, fake_call = _mock_grpc_objects(empty_pb2.Empty())
+    client = operations_v1.OperationsAsyncClient(mocked_channel)
+
+    await client.delete_operation("name", metadata=[("header", "foo")])
+
+    assert method.call_count == 1
+    assert tuple(method.call_args_list[0])[0][0].name == "name"
+    assert ("header", "foo") in tuple(method.call_args_list[0])[1]["metadata"]
+    assert ("x-goog-request-params", "name=name") in tuple(method.call_args_list[0])[1][
+        "metadata"
+    ]
+
+
+@pytest.mark.asyncio
+async def test_cancel_operation():
+    mocked_channel, method, fake_call = _mock_grpc_objects(empty_pb2.Empty())
+    client = operations_v1.OperationsAsyncClient(mocked_channel)
+
+    await client.cancel_operation("name", metadata=[("header", "foo")])
+
+    assert method.call_count == 1
+    assert tuple(method.call_args_list[0])[0][0].name == "name"
+    assert ("header", "foo") in tuple(method.call_args_list[0])[1]["metadata"]
+    assert ("x-goog-request-params", "name=name") in tuple(method.call_args_list[0])[1][
+        "metadata"
+    ]
diff --git a/tests/asyncio/test_grpc_helpers_async.py b/tests/asyncio/test_grpc_helpers_async.py
new file mode 100644
index 0000000..3681a40
--- /dev/null
+++ b/tests/asyncio/test_grpc_helpers_async.py
@@ -0,0 +1,589 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import mock
+import pytest  # noqa: I202
+
+try:
+    import grpc
+    from grpc import aio
+except ImportError:
+    grpc = aio = None
+
+
+if grpc is None:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+
+from google.api_core import exceptions
+from google.api_core import grpc_helpers_async
+import google.auth.credentials
+
+
+class RpcErrorImpl(grpc.RpcError, grpc.Call):
+    def __init__(self, code):
+        super(RpcErrorImpl, self).__init__()
+        self._code = code
+
+    def code(self):
+        return self._code
+
+    def details(self):
+        return None
+
+    def trailing_metadata(self):
+        return None
+
+
+@pytest.mark.asyncio
+async def test_wrap_unary_errors():
+    grpc_error = RpcErrorImpl(grpc.StatusCode.INVALID_ARGUMENT)
+    callable_ = mock.AsyncMock(spec=["__call__"], side_effect=grpc_error)
+
+    wrapped_callable = grpc_helpers_async._wrap_unary_errors(callable_)
+
+    with pytest.raises(exceptions.InvalidArgument) as exc_info:
+        await wrapped_callable(1, 2, three="four")
+
+    callable_.assert_called_once_with(1, 2, three="four")
+    assert exc_info.value.response == grpc_error
+
+
+@pytest.mark.asyncio
+async def test_common_methods_in_wrapped_call():
+    mock_call = mock.Mock(aio.UnaryUnaryCall, autospec=True)
+    wrapped_call = grpc_helpers_async._WrappedUnaryUnaryCall().with_call(mock_call)
+
+    await wrapped_call.initial_metadata()
+    assert mock_call.initial_metadata.call_count == 1
+
+    await wrapped_call.trailing_metadata()
+    assert mock_call.trailing_metadata.call_count == 1
+
+    await wrapped_call.code()
+    assert mock_call.code.call_count == 1
+
+    await wrapped_call.details()
+    assert mock_call.details.call_count == 1
+
+    wrapped_call.cancelled()
+    assert mock_call.cancelled.call_count == 1
+
+    wrapped_call.done()
+    assert mock_call.done.call_count == 1
+
+    wrapped_call.time_remaining()
+    assert mock_call.time_remaining.call_count == 1
+
+    wrapped_call.cancel()
+    assert mock_call.cancel.call_count == 1
+
+    callback = mock.sentinel.callback
+    wrapped_call.add_done_callback(callback)
+    mock_call.add_done_callback.assert_called_once_with(callback)
+
+    await wrapped_call.wait_for_connection()
+    assert mock_call.wait_for_connection.call_count == 1
+
+
+@pytest.mark.asyncio
+async def test_wrap_stream_errors_unary_stream():
+    mock_call = mock.Mock(aio.UnaryStreamCall, autospec=True)
+    multicallable = mock.Mock(return_value=mock_call)
+
+    wrapped_callable = grpc_helpers_async._wrap_stream_errors(multicallable)
+
+    await wrapped_callable(1, 2, three="four")
+    multicallable.assert_called_once_with(1, 2, three="four")
+    assert mock_call.wait_for_connection.call_count == 1
+
+
+@pytest.mark.asyncio
+async def test_wrap_stream_errors_stream_unary():
+    mock_call = mock.Mock(aio.StreamUnaryCall, autospec=True)
+    multicallable = mock.Mock(return_value=mock_call)
+
+    wrapped_callable = grpc_helpers_async._wrap_stream_errors(multicallable)
+
+    await wrapped_callable(1, 2, three="four")
+    multicallable.assert_called_once_with(1, 2, three="four")
+    assert mock_call.wait_for_connection.call_count == 1
+
+
+@pytest.mark.asyncio
+async def test_wrap_stream_errors_stream_stream():
+    mock_call = mock.Mock(aio.StreamStreamCall, autospec=True)
+    multicallable = mock.Mock(return_value=mock_call)
+
+    wrapped_callable = grpc_helpers_async._wrap_stream_errors(multicallable)
+
+    await wrapped_callable(1, 2, three="four")
+    multicallable.assert_called_once_with(1, 2, three="four")
+    assert mock_call.wait_for_connection.call_count == 1
+
+
+@pytest.mark.asyncio
+async def test_wrap_stream_errors_type_error():
+    mock_call = mock.Mock()
+    multicallable = mock.Mock(return_value=mock_call)
+
+    wrapped_callable = grpc_helpers_async._wrap_stream_errors(multicallable)
+
+    with pytest.raises(TypeError):
+        await wrapped_callable()
+
+
+@pytest.mark.asyncio
+async def test_wrap_stream_errors_raised():
+    grpc_error = RpcErrorImpl(grpc.StatusCode.INVALID_ARGUMENT)
+    mock_call = mock.Mock(aio.StreamStreamCall, autospec=True)
+    mock_call.wait_for_connection = mock.AsyncMock(side_effect=[grpc_error])
+    multicallable = mock.Mock(return_value=mock_call)
+
+    wrapped_callable = grpc_helpers_async._wrap_stream_errors(multicallable)
+
+    with pytest.raises(exceptions.InvalidArgument):
+        await wrapped_callable()
+    assert mock_call.wait_for_connection.call_count == 1
+
+
+@pytest.mark.asyncio
+async def test_wrap_stream_errors_read():
+    grpc_error = RpcErrorImpl(grpc.StatusCode.INVALID_ARGUMENT)
+
+    mock_call = mock.Mock(aio.StreamStreamCall, autospec=True)
+    mock_call.read = mock.AsyncMock(side_effect=grpc_error)
+    multicallable = mock.Mock(return_value=mock_call)
+
+    wrapped_callable = grpc_helpers_async._wrap_stream_errors(multicallable)
+
+    wrapped_call = await wrapped_callable(1, 2, three="four")
+    multicallable.assert_called_once_with(1, 2, three="four")
+    assert mock_call.wait_for_connection.call_count == 1
+
+    with pytest.raises(exceptions.InvalidArgument) as exc_info:
+        await wrapped_call.read()
+    assert exc_info.value.response == grpc_error
+
+
+@pytest.mark.asyncio
+async def test_wrap_stream_errors_aiter():
+    grpc_error = RpcErrorImpl(grpc.StatusCode.INVALID_ARGUMENT)
+
+    mock_call = mock.Mock(aio.StreamStreamCall, autospec=True)
+    mocked_aiter = mock.Mock(spec=["__anext__"])
+    mocked_aiter.__anext__ = mock.AsyncMock(
+        side_effect=[mock.sentinel.response, grpc_error]
+    )
+    mock_call.__aiter__ = mock.Mock(return_value=mocked_aiter)
+    multicallable = mock.Mock(return_value=mock_call)
+
+    wrapped_callable = grpc_helpers_async._wrap_stream_errors(multicallable)
+    wrapped_call = await wrapped_callable()
+
+    with pytest.raises(exceptions.InvalidArgument) as exc_info:
+        async for response in wrapped_call:
+            assert response == mock.sentinel.response
+    assert exc_info.value.response == grpc_error
+
+
+@pytest.mark.asyncio
+async def test_wrap_stream_errors_aiter_non_rpc_error():
+    non_grpc_error = TypeError("Not a gRPC error")
+
+    mock_call = mock.Mock(aio.StreamStreamCall, autospec=True)
+    mocked_aiter = mock.Mock(spec=["__anext__"])
+    mocked_aiter.__anext__ = mock.AsyncMock(
+        side_effect=[mock.sentinel.response, non_grpc_error]
+    )
+    mock_call.__aiter__ = mock.Mock(return_value=mocked_aiter)
+    multicallable = mock.Mock(return_value=mock_call)
+
+    wrapped_callable = grpc_helpers_async._wrap_stream_errors(multicallable)
+    wrapped_call = await wrapped_callable()
+
+    with pytest.raises(TypeError) as exc_info:
+        async for response in wrapped_call:
+            assert response == mock.sentinel.response
+    assert exc_info.value == non_grpc_error
+
+
+@pytest.mark.asyncio
+async def test_wrap_stream_errors_aiter_called_multiple_times():
+    mock_call = mock.Mock(aio.StreamStreamCall, autospec=True)
+    multicallable = mock.Mock(return_value=mock_call)
+
+    wrapped_callable = grpc_helpers_async._wrap_stream_errors(multicallable)
+    wrapped_call = await wrapped_callable()
+
+    assert wrapped_call.__aiter__() == wrapped_call.__aiter__()
+
+
+@pytest.mark.asyncio
+async def test_wrap_stream_errors_write():
+    grpc_error = RpcErrorImpl(grpc.StatusCode.INVALID_ARGUMENT)
+
+    mock_call = mock.Mock(aio.StreamStreamCall, autospec=True)
+    mock_call.write = mock.AsyncMock(side_effect=[None, grpc_error])
+    mock_call.done_writing = mock.AsyncMock(side_effect=[None, grpc_error])
+    multicallable = mock.Mock(return_value=mock_call)
+
+    wrapped_callable = grpc_helpers_async._wrap_stream_errors(multicallable)
+
+    wrapped_call = await wrapped_callable()
+
+    await wrapped_call.write(mock.sentinel.request)
+    with pytest.raises(exceptions.InvalidArgument) as exc_info:
+        await wrapped_call.write(mock.sentinel.request)
+    assert mock_call.write.call_count == 2
+    assert exc_info.value.response == grpc_error
+
+    await wrapped_call.done_writing()
+    with pytest.raises(exceptions.InvalidArgument) as exc_info:
+        await wrapped_call.done_writing()
+    assert mock_call.done_writing.call_count == 2
+    assert exc_info.value.response == grpc_error
+
+
+@mock.patch("google.api_core.grpc_helpers_async._wrap_unary_errors")
+def test_wrap_errors_non_streaming(wrap_unary_errors):
+    callable_ = mock.create_autospec(aio.UnaryUnaryMultiCallable)
+
+    result = grpc_helpers_async.wrap_errors(callable_)
+
+    assert result == wrap_unary_errors.return_value
+    wrap_unary_errors.assert_called_once_with(callable_)
+
+
+@mock.patch("google.api_core.grpc_helpers_async._wrap_stream_errors")
+def test_wrap_errors_streaming(wrap_stream_errors):
+    callable_ = mock.create_autospec(aio.UnaryStreamMultiCallable)
+
+    result = grpc_helpers_async.wrap_errors(callable_)
+
+    assert result == wrap_stream_errors.return_value
+    wrap_stream_errors.assert_called_once_with(callable_)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch(
+    "google.auth.default",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.projet),
+)
+@mock.patch("grpc.aio.secure_channel")
+def test_create_channel_implicit(grpc_secure_channel, default, composite_creds_call):
+    target = "example.com:443"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers_async.create_channel(target)
+
+    assert channel is grpc_secure_channel.return_value
+
+    default.assert_called_once_with(scopes=None, default_scopes=None)
+    grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("google.auth.transport.grpc.AuthMetadataPlugin", autospec=True)
+@mock.patch(
+    "google.auth.transport.requests.Request",
+    autospec=True,
+    return_value=mock.sentinel.Request,
+)
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch(
+    "google.auth.default",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.projet),
+)
+@mock.patch("grpc.aio.secure_channel")
+def test_create_channel_implicit_with_default_host(
+    grpc_secure_channel, default, composite_creds_call, request, auth_metadata_plugin
+):
+    target = "example.com:443"
+    default_host = "example.com"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers_async.create_channel(target, default_host=default_host)
+
+    assert channel is grpc_secure_channel.return_value
+
+    default.assert_called_once_with(scopes=None, default_scopes=None)
+    auth_metadata_plugin.assert_called_once_with(
+        mock.sentinel.credentials, mock.sentinel.Request, default_host=default_host
+    )
+    grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch(
+    "google.auth.default",
+    return_value=(mock.sentinel.credentials, mock.sentinel.projet),
+)
+@mock.patch("grpc.aio.secure_channel")
+def test_create_channel_implicit_with_ssl_creds(
+    grpc_secure_channel, default, composite_creds_call
+):
+    target = "example.com:443"
+
+    ssl_creds = grpc.ssl_channel_credentials()
+
+    grpc_helpers_async.create_channel(target, ssl_credentials=ssl_creds)
+
+    default.assert_called_once_with(scopes=None, default_scopes=None)
+    composite_creds_call.assert_called_once_with(ssl_creds, mock.ANY)
+    composite_creds = composite_creds_call.return_value
+    grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch(
+    "google.auth.default",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.projet),
+)
+@mock.patch("grpc.aio.secure_channel")
+def test_create_channel_implicit_with_scopes(
+    grpc_secure_channel, default, composite_creds_call
+):
+    target = "example.com:443"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers_async.create_channel(target, scopes=["one", "two"])
+
+    assert channel is grpc_secure_channel.return_value
+
+    default.assert_called_once_with(scopes=["one", "two"], default_scopes=None)
+    grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch(
+    "google.auth.default",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.projet),
+)
+@mock.patch("grpc.aio.secure_channel")
+def test_create_channel_implicit_with_default_scopes(
+    grpc_secure_channel, default, composite_creds_call
+):
+    target = "example.com:443"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers_async.create_channel(
+        target, default_scopes=["three", "four"]
+    )
+
+    assert channel is grpc_secure_channel.return_value
+
+    default.assert_called_once_with(scopes=None, default_scopes=["three", "four"])
+    grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+def test_create_channel_explicit_with_duplicate_credentials():
+    target = "example:443"
+
+    with pytest.raises(exceptions.DuplicateCredentialArgs) as excinfo:
+        grpc_helpers_async.create_channel(
+            target,
+            credentials_file="credentials.json",
+            credentials=mock.sentinel.credentials,
+        )
+
+    assert "mutually exclusive" in str(excinfo.value)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("google.auth.credentials.with_scopes_if_required", autospec=True)
+@mock.patch("grpc.aio.secure_channel")
+def test_create_channel_explicit(grpc_secure_channel, auth_creds, composite_creds_call):
+    target = "example.com:443"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers_async.create_channel(
+        target, credentials=mock.sentinel.credentials
+    )
+
+    auth_creds.assert_called_once_with(
+        mock.sentinel.credentials, scopes=None, default_scopes=None
+    )
+    assert channel is grpc_secure_channel.return_value
+    grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("grpc.aio.secure_channel")
+def test_create_channel_explicit_scoped(grpc_secure_channel, composite_creds_call):
+    target = "example.com:443"
+    scopes = ["1", "2"]
+    composite_creds = composite_creds_call.return_value
+
+    credentials = mock.create_autospec(google.auth.credentials.Scoped, instance=True)
+    credentials.requires_scopes = True
+
+    channel = grpc_helpers_async.create_channel(
+        target, credentials=credentials, scopes=scopes
+    )
+
+    credentials.with_scopes.assert_called_once_with(scopes, default_scopes=None)
+    assert channel is grpc_secure_channel.return_value
+    grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("grpc.aio.secure_channel")
+def test_create_channel_explicit_default_scopes(
+    grpc_secure_channel, composite_creds_call
+):
+    target = "example.com:443"
+    default_scopes = ["3", "4"]
+    composite_creds = composite_creds_call.return_value
+
+    credentials = mock.create_autospec(google.auth.credentials.Scoped, instance=True)
+    credentials.requires_scopes = True
+
+    channel = grpc_helpers_async.create_channel(
+        target, credentials=credentials, default_scopes=default_scopes
+    )
+
+    credentials.with_scopes.assert_called_once_with(
+        scopes=None, default_scopes=default_scopes
+    )
+    assert channel is grpc_secure_channel.return_value
+    grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("grpc.aio.secure_channel")
+def test_create_channel_explicit_with_quota_project(
+    grpc_secure_channel, composite_creds_call
+):
+    target = "example.com:443"
+    composite_creds = composite_creds_call.return_value
+
+    credentials = mock.create_autospec(
+        google.auth.credentials.CredentialsWithQuotaProject, instance=True
+    )
+
+    channel = grpc_helpers_async.create_channel(
+        target, credentials=credentials, quota_project_id="project-foo"
+    )
+
+    credentials.with_quota_project.assert_called_once_with("project-foo")
+    assert channel is grpc_secure_channel.return_value
+    grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("grpc.aio.secure_channel")
+@mock.patch(
+    "google.auth.load_credentials_from_file",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.project),
+)
+def test_create_channnel_with_credentials_file(
+    load_credentials_from_file, grpc_secure_channel, composite_creds_call
+):
+    target = "example.com:443"
+
+    credentials_file = "/path/to/credentials/file.json"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers_async.create_channel(
+        target, credentials_file=credentials_file
+    )
+
+    google.auth.load_credentials_from_file.assert_called_once_with(
+        credentials_file, scopes=None, default_scopes=None
+    )
+    assert channel is grpc_secure_channel.return_value
+    grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("grpc.aio.secure_channel")
+@mock.patch(
+    "google.auth.load_credentials_from_file",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.project),
+)
+def test_create_channel_with_credentials_file_and_scopes(
+    load_credentials_from_file, grpc_secure_channel, composite_creds_call
+):
+    target = "example.com:443"
+    scopes = ["1", "2"]
+
+    credentials_file = "/path/to/credentials/file.json"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers_async.create_channel(
+        target, credentials_file=credentials_file, scopes=scopes
+    )
+
+    google.auth.load_credentials_from_file.assert_called_once_with(
+        credentials_file, scopes=scopes, default_scopes=None
+    )
+    assert channel is grpc_secure_channel.return_value
+    grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("grpc.aio.secure_channel")
+@mock.patch(
+    "google.auth.load_credentials_from_file",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.project),
+)
+def test_create_channel_with_credentials_file_and_default_scopes(
+    load_credentials_from_file, grpc_secure_channel, composite_creds_call
+):
+    target = "example.com:443"
+    default_scopes = ["3", "4"]
+
+    credentials_file = "/path/to/credentials/file.json"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers_async.create_channel(
+        target, credentials_file=credentials_file, default_scopes=default_scopes
+    )
+
+    google.auth.load_credentials_from_file.assert_called_once_with(
+        credentials_file, scopes=None, default_scopes=default_scopes
+    )
+    assert channel is grpc_secure_channel.return_value
+    grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@pytest.mark.skipif(
+    grpc_helpers_async.HAS_GRPC_GCP, reason="grpc_gcp module not available"
+)
+@mock.patch("grpc.aio.secure_channel")
+def test_create_channel_without_grpc_gcp(grpc_secure_channel):
+    target = "example.com:443"
+    scopes = ["test_scope"]
+
+    credentials = mock.create_autospec(google.auth.credentials.Scoped, instance=True)
+    credentials.requires_scopes = True
+
+    grpc_helpers_async.create_channel(target, credentials=credentials, scopes=scopes)
+    grpc_secure_channel.assert_called()
+    credentials.with_scopes.assert_called_once_with(scopes, default_scopes=None)
+
+
+@pytest.mark.asyncio
+async def test_fake_stream_unary_call():
+    fake_call = grpc_helpers_async.FakeStreamUnaryCall()
+    await fake_call.wait_for_connection()
+    response = await fake_call
+    assert fake_call.response == response
diff --git a/tests/asyncio/test_operation_async.py b/tests/asyncio/test_operation_async.py
new file mode 100644
index 0000000..26ad7ce
--- /dev/null
+++ b/tests/asyncio/test_operation_async.py
@@ -0,0 +1,201 @@
+# Copyright 2017, Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import mock
+import pytest
+
+try:
+    import grpc  # noqa: F401
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+from google.api_core import exceptions
+from google.api_core import operation_async
+from google.api_core import operations_v1
+from google.api_core import retry_async
+from google.longrunning import operations_pb2
+from google.protobuf import struct_pb2
+from google.rpc import code_pb2
+from google.rpc import status_pb2
+
+TEST_OPERATION_NAME = "test/operation"
+
+
+def make_operation_proto(
+    name=TEST_OPERATION_NAME, metadata=None, response=None, error=None, **kwargs
+):
+    operation_proto = operations_pb2.Operation(name=name, **kwargs)
+
+    if metadata is not None:
+        operation_proto.metadata.Pack(metadata)
+
+    if response is not None:
+        operation_proto.response.Pack(response)
+
+    if error is not None:
+        operation_proto.error.CopyFrom(error)
+
+    return operation_proto
+
+
+def make_operation_future(client_operations_responses=None):
+    if client_operations_responses is None:
+        client_operations_responses = [make_operation_proto()]
+
+    refresh = mock.AsyncMock(spec=["__call__"], side_effect=client_operations_responses)
+    refresh.responses = client_operations_responses
+    cancel = mock.AsyncMock(spec=["__call__"])
+    operation_future = operation_async.AsyncOperation(
+        client_operations_responses[0],
+        refresh,
+        cancel,
+        result_type=struct_pb2.Struct,
+        metadata_type=struct_pb2.Struct,
+    )
+
+    return operation_future, refresh, cancel
+
+
+@pytest.mark.asyncio
+async def test_constructor():
+    future, refresh, _ = make_operation_future()
+
+    assert future.operation == refresh.responses[0]
+    assert future.operation.done is False
+    assert future.operation.name == TEST_OPERATION_NAME
+    assert future.metadata is None
+    assert await future.running()
+
+
+def test_metadata():
+    expected_metadata = struct_pb2.Struct()
+    future, _, _ = make_operation_future(
+        [make_operation_proto(metadata=expected_metadata)]
+    )
+
+    assert future.metadata == expected_metadata
+
+
+@pytest.mark.asyncio
+async def test_cancellation():
+    responses = [
+        make_operation_proto(),
+        # Second response indicates that the operation was cancelled.
+        make_operation_proto(
+            done=True, error=status_pb2.Status(code=code_pb2.CANCELLED)
+        ),
+    ]
+    future, _, cancel = make_operation_future(responses)
+
+    assert await future.cancel()
+    assert await future.cancelled()
+    cancel.assert_called_once_with()
+
+    # Cancelling twice should have no effect.
+    assert not await future.cancel()
+    cancel.assert_called_once_with()
+
+
+@pytest.mark.asyncio
+async def test_result():
+    expected_result = struct_pb2.Struct()
+    responses = [
+        make_operation_proto(),
+        # Second operation response includes the result.
+        make_operation_proto(done=True, response=expected_result),
+    ]
+    future, _, _ = make_operation_future(responses)
+
+    result = await future.result()
+
+    assert result == expected_result
+    assert await future.done()
+
+
+@pytest.mark.asyncio
+async def test_done_w_retry():
+    RETRY_PREDICATE = retry_async.if_exception_type(exceptions.TooManyRequests)
+    test_retry = retry_async.AsyncRetry(predicate=RETRY_PREDICATE)
+
+    expected_result = struct_pb2.Struct()
+    responses = [
+        make_operation_proto(),
+        # Second operation response includes the result.
+        make_operation_proto(done=True, response=expected_result),
+    ]
+    future, refresh, _ = make_operation_future(responses)
+
+    await future.done(retry=test_retry)
+    refresh.assert_called_once_with(retry=test_retry)
+
+
+@pytest.mark.asyncio
+async def test_exception():
+    expected_exception = status_pb2.Status(message="meep")
+    responses = [
+        make_operation_proto(),
+        # Second operation response includes the error.
+        make_operation_proto(done=True, error=expected_exception),
+    ]
+    future, _, _ = make_operation_future(responses)
+
+    exception = await future.exception()
+
+    assert expected_exception.message in "{!r}".format(exception)
+
+
+@mock.patch("asyncio.sleep", autospec=True)
+@pytest.mark.asyncio
+async def test_unexpected_result(unused_sleep):
+    responses = [
+        make_operation_proto(),
+        # Second operation response is done, but has not error or response.
+        make_operation_proto(done=True),
+    ]
+    future, _, _ = make_operation_future(responses)
+
+    exception = await future.exception()
+
+    assert "Unexpected state" in "{!r}".format(exception)
+
+
+def test_from_gapic():
+    operation_proto = make_operation_proto(done=True)
+    operations_client = mock.create_autospec(
+        operations_v1.OperationsClient, instance=True
+    )
+
+    future = operation_async.from_gapic(
+        operation_proto,
+        operations_client,
+        struct_pb2.Struct,
+        metadata_type=struct_pb2.Struct,
+        grpc_metadata=[("x-goog-request-params", "foo")],
+    )
+
+    assert future._result_type == struct_pb2.Struct
+    assert future._metadata_type == struct_pb2.Struct
+    assert future.operation.name == TEST_OPERATION_NAME
+    assert future.done
+    assert future._refresh.keywords["metadata"] == [("x-goog-request-params", "foo")]
+    assert future._cancel.keywords["metadata"] == [("x-goog-request-params", "foo")]
+
+
+def test_deserialize():
+    op = make_operation_proto(name="foobarbaz")
+    serialized = op.SerializeToString()
+    deserialized_op = operation_async.AsyncOperation.deserialize(serialized)
+    assert op.name == deserialized_op.name
+    assert type(op) is type(deserialized_op)
diff --git a/tests/asyncio/test_page_iterator_async.py b/tests/asyncio/test_page_iterator_async.py
new file mode 100644
index 0000000..75f9e1c
--- /dev/null
+++ b/tests/asyncio/test_page_iterator_async.py
@@ -0,0 +1,290 @@
+# Copyright 2015 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import inspect
+
+import mock
+import pytest
+
+from google.api_core import page_iterator_async
+
+
+class PageAsyncIteratorImpl(page_iterator_async.AsyncIterator):
+    async def _next_page(self):
+        return mock.create_autospec(page_iterator_async.Page, instance=True)
+
+
+class TestAsyncIterator:
+    def test_constructor(self):
+        client = mock.sentinel.client
+        item_to_value = mock.sentinel.item_to_value
+        token = "ab13nceor03"
+        max_results = 1337
+
+        iterator = PageAsyncIteratorImpl(
+            client, item_to_value, page_token=token, max_results=max_results
+        )
+
+        assert not iterator._started
+        assert iterator.client is client
+        assert iterator.item_to_value == item_to_value
+        assert iterator.max_results == max_results
+        # Changing attributes.
+        assert iterator.page_number == 0
+        assert iterator.next_page_token == token
+        assert iterator.num_results == 0
+
+    @pytest.mark.asyncio
+    async def test_anext(self):
+        parent = mock.sentinel.parent
+        page_1 = page_iterator_async.Page(
+            parent,
+            ("item 1.1", "item 1.2"),
+            page_iterator_async._item_to_value_identity,
+        )
+        page_2 = page_iterator_async.Page(
+            parent, ("item 2.1",), page_iterator_async._item_to_value_identity
+        )
+
+        async_iterator = PageAsyncIteratorImpl(None, None)
+        async_iterator._next_page = mock.AsyncMock(side_effect=[page_1, page_2, None])
+
+        # Consume items and check the state of the async_iterator.
+        assert async_iterator.num_results == 0
+        assert await async_iterator.__anext__() == "item 1.1"
+        assert async_iterator.num_results == 1
+
+        assert await async_iterator.__anext__() == "item 1.2"
+        assert async_iterator.num_results == 2
+
+        assert await async_iterator.__anext__() == "item 2.1"
+        assert async_iterator.num_results == 3
+
+        with pytest.raises(StopAsyncIteration):
+            await async_iterator.__anext__()
+
+    def test_pages_property_starts(self):
+        iterator = PageAsyncIteratorImpl(None, None)
+
+        assert not iterator._started
+
+        assert inspect.isasyncgen(iterator.pages)
+
+        assert iterator._started
+
+    def test_pages_property_restart(self):
+        iterator = PageAsyncIteratorImpl(None, None)
+
+        assert iterator.pages
+
+        # Make sure we cannot restart.
+        with pytest.raises(ValueError):
+            assert iterator.pages
+
+    @pytest.mark.asyncio
+    async def test__page_aiter_increment(self):
+        iterator = PageAsyncIteratorImpl(None, None)
+        page = page_iterator_async.Page(
+            iterator, ("item",), page_iterator_async._item_to_value_identity
+        )
+        iterator._next_page = mock.AsyncMock(side_effect=[page, None])
+
+        assert iterator.num_results == 0
+
+        page_aiter = iterator._page_aiter(increment=True)
+        await page_aiter.__anext__()
+
+        assert iterator.num_results == 1
+
+    @pytest.mark.asyncio
+    async def test__page_aiter_no_increment(self):
+        iterator = PageAsyncIteratorImpl(None, None)
+
+        assert iterator.num_results == 0
+
+        page_aiter = iterator._page_aiter(increment=False)
+        await page_aiter.__anext__()
+
+        # results should still be 0 after fetching a page.
+        assert iterator.num_results == 0
+
+    @pytest.mark.asyncio
+    async def test__items_aiter(self):
+        # Items to be returned.
+        item1 = 17
+        item2 = 100
+        item3 = 211
+
+        # Make pages from mock responses
+        parent = mock.sentinel.parent
+        page1 = page_iterator_async.Page(
+            parent, (item1, item2), page_iterator_async._item_to_value_identity
+        )
+        page2 = page_iterator_async.Page(
+            parent, (item3,), page_iterator_async._item_to_value_identity
+        )
+
+        iterator = PageAsyncIteratorImpl(None, None)
+        iterator._next_page = mock.AsyncMock(side_effect=[page1, page2, None])
+
+        items_aiter = iterator._items_aiter()
+
+        assert inspect.isasyncgen(items_aiter)
+
+        # Consume items and check the state of the iterator.
+        assert iterator.num_results == 0
+        assert await items_aiter.__anext__() == item1
+        assert iterator.num_results == 1
+
+        assert await items_aiter.__anext__() == item2
+        assert iterator.num_results == 2
+
+        assert await items_aiter.__anext__() == item3
+        assert iterator.num_results == 3
+
+        with pytest.raises(StopAsyncIteration):
+            await items_aiter.__anext__()
+
+    @pytest.mark.asyncio
+    async def test___aiter__(self):
+        async_iterator = PageAsyncIteratorImpl(None, None)
+        async_iterator._next_page = mock.AsyncMock(side_effect=[(1, 2), (3,), None])
+
+        assert not async_iterator._started
+
+        result = []
+        async for item in async_iterator:
+            result.append(item)
+
+        assert result == [1, 2, 3]
+        assert async_iterator._started
+
+    def test___aiter__restart(self):
+        iterator = PageAsyncIteratorImpl(None, None)
+
+        iterator.__aiter__()
+
+        # Make sure we cannot restart.
+        with pytest.raises(ValueError):
+            iterator.__aiter__()
+
+    def test___aiter___restart_after_page(self):
+        iterator = PageAsyncIteratorImpl(None, None)
+
+        assert iterator.pages
+
+        # Make sure we cannot restart after starting the page iterator
+        with pytest.raises(ValueError):
+            iterator.__aiter__()
+
+
+class TestAsyncGRPCIterator(object):
+    def test_constructor(self):
+        client = mock.sentinel.client
+        items_field = "items"
+        iterator = page_iterator_async.AsyncGRPCIterator(
+            client, mock.sentinel.method, mock.sentinel.request, items_field
+        )
+
+        assert not iterator._started
+        assert iterator.client is client
+        assert iterator.max_results is None
+        assert iterator.item_to_value is page_iterator_async._item_to_value_identity
+        assert iterator._method == mock.sentinel.method
+        assert iterator._request == mock.sentinel.request
+        assert iterator._items_field == items_field
+        assert (
+            iterator._request_token_field
+            == page_iterator_async.AsyncGRPCIterator._DEFAULT_REQUEST_TOKEN_FIELD
+        )
+        assert (
+            iterator._response_token_field
+            == page_iterator_async.AsyncGRPCIterator._DEFAULT_RESPONSE_TOKEN_FIELD
+        )
+        # Changing attributes.
+        assert iterator.page_number == 0
+        assert iterator.next_page_token is None
+        assert iterator.num_results == 0
+
+    def test_constructor_options(self):
+        client = mock.sentinel.client
+        items_field = "items"
+        request_field = "request"
+        response_field = "response"
+        iterator = page_iterator_async.AsyncGRPCIterator(
+            client,
+            mock.sentinel.method,
+            mock.sentinel.request,
+            items_field,
+            item_to_value=mock.sentinel.item_to_value,
+            request_token_field=request_field,
+            response_token_field=response_field,
+            max_results=42,
+        )
+
+        assert iterator.client is client
+        assert iterator.max_results == 42
+        assert iterator.item_to_value is mock.sentinel.item_to_value
+        assert iterator._method == mock.sentinel.method
+        assert iterator._request == mock.sentinel.request
+        assert iterator._items_field == items_field
+        assert iterator._request_token_field == request_field
+        assert iterator._response_token_field == response_field
+
+    @pytest.mark.asyncio
+    async def test_iterate(self):
+        request = mock.Mock(spec=["page_token"], page_token=None)
+        response1 = mock.Mock(items=["a", "b"], next_page_token="1")
+        response2 = mock.Mock(items=["c"], next_page_token="2")
+        response3 = mock.Mock(items=["d"], next_page_token="")
+        method = mock.AsyncMock(side_effect=[response1, response2, response3])
+        iterator = page_iterator_async.AsyncGRPCIterator(
+            mock.sentinel.client, method, request, "items"
+        )
+
+        assert iterator.num_results == 0
+
+        items = []
+        async for item in iterator:
+            items.append(item)
+
+        assert items == ["a", "b", "c", "d"]
+
+        method.assert_called_with(request)
+        assert method.call_count == 3
+        assert request.page_token == "2"
+
+    @pytest.mark.asyncio
+    async def test_iterate_with_max_results(self):
+        request = mock.Mock(spec=["page_token"], page_token=None)
+        response1 = mock.Mock(items=["a", "b"], next_page_token="1")
+        response2 = mock.Mock(items=["c"], next_page_token="2")
+        response3 = mock.Mock(items=["d"], next_page_token="")
+        method = mock.AsyncMock(side_effect=[response1, response2, response3])
+        iterator = page_iterator_async.AsyncGRPCIterator(
+            mock.sentinel.client, method, request, "items", max_results=3
+        )
+
+        assert iterator.num_results == 0
+
+        items = []
+        async for item in iterator:
+            items.append(item)
+
+        assert items == ["a", "b", "c"]
+        assert iterator.num_results == 3
+
+        method.assert_called_with(request)
+        assert method.call_count == 2
+        assert request.page_token == "1"
diff --git a/tests/asyncio/test_retry_async.py b/tests/asyncio/test_retry_async.py
new file mode 100644
index 0000000..9e51044
--- /dev/null
+++ b/tests/asyncio/test_retry_async.py
@@ -0,0 +1,403 @@
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import datetime
+import re
+
+import mock
+import pytest
+
+from google.api_core import exceptions
+from google.api_core import retry_async
+
+
+@mock.patch("asyncio.sleep", autospec=True)
+@mock.patch(
+    "google.api_core.datetime_helpers.utcnow",
+    return_value=datetime.datetime.min,
+    autospec=True,
+)
+@pytest.mark.asyncio
+async def test_retry_target_success(utcnow, sleep):
+    predicate = retry_async.if_exception_type(ValueError)
+    call_count = [0]
+
+    async def target():
+        call_count[0] += 1
+        if call_count[0] < 3:
+            raise ValueError()
+        return 42
+
+    result = await retry_async.retry_target(target, predicate, range(10), None)
+
+    assert result == 42
+    assert call_count[0] == 3
+    sleep.assert_has_calls([mock.call(0), mock.call(1)])
+
+
+@mock.patch("asyncio.sleep", autospec=True)
+@mock.patch(
+    "google.api_core.datetime_helpers.utcnow",
+    return_value=datetime.datetime.min,
+    autospec=True,
+)
+@pytest.mark.asyncio
+async def test_retry_target_w_on_error(utcnow, sleep):
+    predicate = retry_async.if_exception_type(ValueError)
+    call_count = {"target": 0}
+    to_raise = ValueError()
+
+    async def target():
+        call_count["target"] += 1
+        if call_count["target"] < 3:
+            raise to_raise
+        return 42
+
+    on_error = mock.Mock()
+
+    result = await retry_async.retry_target(
+        target, predicate, range(10), None, on_error=on_error
+    )
+
+    assert result == 42
+    assert call_count["target"] == 3
+
+    on_error.assert_has_calls([mock.call(to_raise), mock.call(to_raise)])
+    sleep.assert_has_calls([mock.call(0), mock.call(1)])
+
+
+@mock.patch("asyncio.sleep", autospec=True)
+@mock.patch(
+    "google.api_core.datetime_helpers.utcnow",
+    return_value=datetime.datetime.min,
+    autospec=True,
+)
+@pytest.mark.asyncio
+async def test_retry_target_non_retryable_error(utcnow, sleep):
+    predicate = retry_async.if_exception_type(ValueError)
+    exception = TypeError()
+    target = mock.Mock(side_effect=exception)
+
+    with pytest.raises(TypeError) as exc_info:
+        await retry_async.retry_target(target, predicate, range(10), None)
+
+    assert exc_info.value == exception
+    sleep.assert_not_called()
+
+
+@mock.patch("asyncio.sleep", autospec=True)
+@mock.patch("google.api_core.datetime_helpers.utcnow", autospec=True)
+@pytest.mark.asyncio
+async def test_retry_target_deadline_exceeded(utcnow, sleep):
+    predicate = retry_async.if_exception_type(ValueError)
+    exception = ValueError("meep")
+    target = mock.Mock(side_effect=exception)
+    # Setup the timeline so that the first call takes 5 seconds but the second
+    # call takes 6, which puts the retry over the deadline.
+    utcnow.side_effect = [
+        # The first call to utcnow establishes the start of the timeline.
+        datetime.datetime.min,
+        datetime.datetime.min + datetime.timedelta(seconds=5),
+        datetime.datetime.min + datetime.timedelta(seconds=11),
+    ]
+
+    with pytest.raises(exceptions.RetryError) as exc_info:
+        await retry_async.retry_target(target, predicate, range(10), deadline=10)
+
+    assert exc_info.value.cause == exception
+    assert exc_info.match("Deadline of 10.0s exceeded")
+    assert exc_info.match("last exception: meep")
+    assert target.call_count == 2
+
+
+@pytest.mark.asyncio
+async def test_retry_target_bad_sleep_generator():
+    with pytest.raises(ValueError, match="Sleep generator"):
+        await retry_async.retry_target(
+            mock.sentinel.target, mock.sentinel.predicate, [], None
+        )
+
+
+class TestAsyncRetry:
+    def test_constructor_defaults(self):
+        retry_ = retry_async.AsyncRetry()
+        assert retry_._predicate == retry_async.if_transient_error
+        assert retry_._initial == 1
+        assert retry_._maximum == 60
+        assert retry_._multiplier == 2
+        assert retry_._deadline == 120
+        assert retry_._on_error is None
+
+    def test_constructor_options(self):
+        _some_function = mock.Mock()
+
+        retry_ = retry_async.AsyncRetry(
+            predicate=mock.sentinel.predicate,
+            initial=1,
+            maximum=2,
+            multiplier=3,
+            deadline=4,
+            on_error=_some_function,
+        )
+        assert retry_._predicate == mock.sentinel.predicate
+        assert retry_._initial == 1
+        assert retry_._maximum == 2
+        assert retry_._multiplier == 3
+        assert retry_._deadline == 4
+        assert retry_._on_error is _some_function
+
+    def test_with_deadline(self):
+        retry_ = retry_async.AsyncRetry(
+            predicate=mock.sentinel.predicate,
+            initial=1,
+            maximum=2,
+            multiplier=3,
+            deadline=4,
+            on_error=mock.sentinel.on_error,
+        )
+        new_retry = retry_.with_deadline(42)
+        assert retry_ is not new_retry
+        assert new_retry._deadline == 42
+
+        # the rest of the attributes should remain the same
+        assert new_retry._predicate is retry_._predicate
+        assert new_retry._initial == retry_._initial
+        assert new_retry._maximum == retry_._maximum
+        assert new_retry._multiplier == retry_._multiplier
+        assert new_retry._on_error is retry_._on_error
+
+    def test_with_predicate(self):
+        retry_ = retry_async.AsyncRetry(
+            predicate=mock.sentinel.predicate,
+            initial=1,
+            maximum=2,
+            multiplier=3,
+            deadline=4,
+            on_error=mock.sentinel.on_error,
+        )
+        new_retry = retry_.with_predicate(mock.sentinel.predicate)
+        assert retry_ is not new_retry
+        assert new_retry._predicate == mock.sentinel.predicate
+
+        # the rest of the attributes should remain the same
+        assert new_retry._deadline == retry_._deadline
+        assert new_retry._initial == retry_._initial
+        assert new_retry._maximum == retry_._maximum
+        assert new_retry._multiplier == retry_._multiplier
+        assert new_retry._on_error is retry_._on_error
+
+    def test_with_delay_noop(self):
+        retry_ = retry_async.AsyncRetry(
+            predicate=mock.sentinel.predicate,
+            initial=1,
+            maximum=2,
+            multiplier=3,
+            deadline=4,
+            on_error=mock.sentinel.on_error,
+        )
+        new_retry = retry_.with_delay()
+        assert retry_ is not new_retry
+        assert new_retry._initial == retry_._initial
+        assert new_retry._maximum == retry_._maximum
+        assert new_retry._multiplier == retry_._multiplier
+
+    def test_with_delay(self):
+        retry_ = retry_async.AsyncRetry(
+            predicate=mock.sentinel.predicate,
+            initial=1,
+            maximum=2,
+            multiplier=3,
+            deadline=4,
+            on_error=mock.sentinel.on_error,
+        )
+        new_retry = retry_.with_delay(initial=1, maximum=2, multiplier=3)
+        assert retry_ is not new_retry
+        assert new_retry._initial == 1
+        assert new_retry._maximum == 2
+        assert new_retry._multiplier == 3
+
+        # the rest of the attributes should remain the same
+        assert new_retry._deadline == retry_._deadline
+        assert new_retry._predicate is retry_._predicate
+        assert new_retry._on_error is retry_._on_error
+
+    def test___str__(self):
+        def if_exception_type(exc):
+            return bool(exc)  # pragma: NO COVER
+
+        # Explicitly set all attributes as changed Retry defaults should not
+        # cause this test to start failing.
+        retry_ = retry_async.AsyncRetry(
+            predicate=if_exception_type,
+            initial=1.0,
+            maximum=60.0,
+            multiplier=2.0,
+            deadline=120.0,
+            on_error=None,
+        )
+        assert re.match(
+            (
+                r"<AsyncRetry predicate=<function.*?if_exception_type.*?>, "
+                r"initial=1.0, maximum=60.0, multiplier=2.0, deadline=120.0, "
+                r"on_error=None>"
+            ),
+            str(retry_),
+        )
+
+    @mock.patch("asyncio.sleep", autospec=True)
+    @pytest.mark.asyncio
+    async def test___call___and_execute_success(self, sleep):
+        retry_ = retry_async.AsyncRetry()
+        target = mock.AsyncMock(spec=["__call__"], return_value=42)
+        # __name__ is needed by functools.partial.
+        target.__name__ = "target"
+
+        decorated = retry_(target)
+        target.assert_not_called()
+
+        result = await decorated("meep")
+
+        assert result == 42
+        target.assert_called_once_with("meep")
+        sleep.assert_not_called()
+
+    # Make uniform return half of its maximum, which is the calculated sleep time.
+    @mock.patch("random.uniform", autospec=True, side_effect=lambda m, n: n / 2.0)
+    @mock.patch("asyncio.sleep", autospec=True)
+    @pytest.mark.asyncio
+    async def test___call___and_execute_retry(self, sleep, uniform):
+
+        on_error = mock.Mock(spec=["__call__"], side_effect=[None])
+        retry_ = retry_async.AsyncRetry(
+            predicate=retry_async.if_exception_type(ValueError)
+        )
+
+        target = mock.AsyncMock(spec=["__call__"], side_effect=[ValueError(), 42])
+        # __name__ is needed by functools.partial.
+        target.__name__ = "target"
+
+        decorated = retry_(target, on_error=on_error)
+        target.assert_not_called()
+
+        result = await decorated("meep")
+
+        assert result == 42
+        assert target.call_count == 2
+        target.assert_has_calls([mock.call("meep"), mock.call("meep")])
+        sleep.assert_called_once_with(retry_._initial)
+        assert on_error.call_count == 1
+
+    # Make uniform return half of its maximum, which is the calculated sleep time.
+    @mock.patch("random.uniform", autospec=True, side_effect=lambda m, n: n / 2.0)
+    @mock.patch("asyncio.sleep", autospec=True)
+    @pytest.mark.asyncio
+    async def test___call___and_execute_retry_hitting_deadline(self, sleep, uniform):
+
+        on_error = mock.Mock(spec=["__call__"], side_effect=[None] * 10)
+        retry_ = retry_async.AsyncRetry(
+            predicate=retry_async.if_exception_type(ValueError),
+            initial=1.0,
+            maximum=1024.0,
+            multiplier=2.0,
+            deadline=9.9,
+        )
+
+        utcnow = datetime.datetime.utcnow()
+        utcnow_patcher = mock.patch(
+            "google.api_core.datetime_helpers.utcnow", return_value=utcnow
+        )
+
+        target = mock.AsyncMock(spec=["__call__"], side_effect=[ValueError()] * 10)
+        # __name__ is needed by functools.partial.
+        target.__name__ = "target"
+
+        decorated = retry_(target, on_error=on_error)
+        target.assert_not_called()
+
+        with utcnow_patcher as patched_utcnow:
+            # Make sure that calls to fake asyncio.sleep() also advance the mocked
+            # time clock.
+            def increase_time(sleep_delay):
+                patched_utcnow.return_value += datetime.timedelta(seconds=sleep_delay)
+
+            sleep.side_effect = increase_time
+
+            with pytest.raises(exceptions.RetryError):
+                await decorated("meep")
+
+        assert target.call_count == 5
+        target.assert_has_calls([mock.call("meep")] * 5)
+        assert on_error.call_count == 5
+
+        # check the delays
+        assert sleep.call_count == 4  # once between each successive target calls
+        last_wait = sleep.call_args.args[0]
+        total_wait = sum(call_args.args[0] for call_args in sleep.call_args_list)
+
+        assert last_wait == 2.9  # and not 8.0, because the last delay was shortened
+        assert total_wait == 9.9  # the same as the deadline
+
+    @mock.patch("asyncio.sleep", autospec=True)
+    @pytest.mark.asyncio
+    async def test___init___without_retry_executed(self, sleep):
+        _some_function = mock.Mock()
+
+        retry_ = retry_async.AsyncRetry(
+            predicate=retry_async.if_exception_type(ValueError), on_error=_some_function
+        )
+        # check the proper creation of the class
+        assert retry_._on_error is _some_function
+
+        target = mock.AsyncMock(spec=["__call__"], side_effect=[42])
+        # __name__ is needed by functools.partial.
+        target.__name__ = "target"
+
+        wrapped = retry_(target)
+
+        result = await wrapped("meep")
+
+        assert result == 42
+        target.assert_called_once_with("meep")
+        sleep.assert_not_called()
+        _some_function.assert_not_called()
+
+    # Make uniform return half of its maximum, which is the calculated sleep time.
+    @mock.patch("random.uniform", autospec=True, side_effect=lambda m, n: n / 2.0)
+    @mock.patch("asyncio.sleep", autospec=True)
+    @pytest.mark.asyncio
+    async def test___init___when_retry_is_executed(self, sleep, uniform):
+        _some_function = mock.Mock()
+
+        retry_ = retry_async.AsyncRetry(
+            predicate=retry_async.if_exception_type(ValueError), on_error=_some_function
+        )
+        # check the proper creation of the class
+        assert retry_._on_error is _some_function
+
+        target = mock.AsyncMock(
+            spec=["__call__"], side_effect=[ValueError(), ValueError(), 42]
+        )
+        # __name__ is needed by functools.partial.
+        target.__name__ = "target"
+
+        wrapped = retry_(target)
+        target.assert_not_called()
+
+        result = await wrapped("meep")
+
+        assert result == 42
+        assert target.call_count == 3
+        assert _some_function.call_count == 2
+        target.assert_has_calls([mock.call("meep"), mock.call("meep")])
+        sleep.assert_any_call(retry_._initial)
diff --git a/tests/unit/__init__.py b/tests/unit/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/unit/__init__.py
diff --git a/tests/unit/future/__init__.py b/tests/unit/future/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/unit/future/__init__.py
diff --git a/tests/unit/future/test__helpers.py b/tests/unit/future/test__helpers.py
new file mode 100644
index 0000000..98afc59
--- /dev/null
+++ b/tests/unit/future/test__helpers.py
@@ -0,0 +1,37 @@
+# Copyright 2017, Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import mock
+
+from google.api_core.future import _helpers
+
+
+@mock.patch("threading.Thread", autospec=True)
+def test_start_deamon_thread(unused_thread):
+    deamon_thread = _helpers.start_daemon_thread(target=mock.sentinel.target)
+    assert deamon_thread.daemon is True
+
+
+def test_safe_invoke_callback():
+    callback = mock.Mock(spec=["__call__"], return_value=42)
+    result = _helpers.safe_invoke_callback(callback, "a", b="c")
+    assert result == 42
+    callback.assert_called_once_with("a", b="c")
+
+
+def test_safe_invoke_callback_exception():
+    callback = mock.Mock(spec=["__call__"], side_effect=ValueError())
+    result = _helpers.safe_invoke_callback(callback, "a", b="c")
+    assert result is None
+    callback.assert_called_once_with("a", b="c")
diff --git a/tests/unit/future/test_polling.py b/tests/unit/future/test_polling.py
new file mode 100644
index 0000000..2381d03
--- /dev/null
+++ b/tests/unit/future/test_polling.py
@@ -0,0 +1,242 @@
+# Copyright 2017, Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import concurrent.futures
+import threading
+import time
+
+import mock
+import pytest
+
+from google.api_core import exceptions, retry
+from google.api_core.future import polling
+
+
+class PollingFutureImpl(polling.PollingFuture):
+    def done(self):
+        return False
+
+    def cancel(self):
+        return True
+
+    def cancelled(self):
+        return False
+
+    def running(self):
+        return True
+
+
+def test_polling_future_constructor():
+    future = PollingFutureImpl()
+    assert not future.done()
+    assert not future.cancelled()
+    assert future.running()
+    assert future.cancel()
+    with mock.patch.object(future, "done", return_value=True):
+        future.result()
+
+
+def test_set_result():
+    future = PollingFutureImpl()
+    callback = mock.Mock()
+
+    future.set_result(1)
+
+    assert future.result() == 1
+    future.add_done_callback(callback)
+    callback.assert_called_once_with(future)
+
+
+def test_set_exception():
+    future = PollingFutureImpl()
+    exception = ValueError("meep")
+
+    future.set_exception(exception)
+
+    assert future.exception() == exception
+    with pytest.raises(ValueError):
+        future.result()
+
+    callback = mock.Mock()
+    future.add_done_callback(callback)
+    callback.assert_called_once_with(future)
+
+
+def test_invoke_callback_exception():
+    future = PollingFutureImplWithPoll()
+    future.set_result(42)
+
+    # This should not raise, despite the callback causing an exception.
+    callback = mock.Mock(side_effect=ValueError)
+    future.add_done_callback(callback)
+    callback.assert_called_once_with(future)
+
+
+class PollingFutureImplWithPoll(PollingFutureImpl):
+    def __init__(self):
+        super(PollingFutureImplWithPoll, self).__init__()
+        self.poll_count = 0
+        self.event = threading.Event()
+
+    def done(self, retry=polling.DEFAULT_RETRY):
+        self.poll_count += 1
+        self.event.wait()
+        self.set_result(42)
+        return True
+
+
+def test_result_with_polling():
+    future = PollingFutureImplWithPoll()
+
+    future.event.set()
+    result = future.result()
+
+    assert result == 42
+    assert future.poll_count == 1
+    # Repeated calls should not cause additional polling
+    assert future.result() == result
+    assert future.poll_count == 1
+
+
+class PollingFutureImplTimeout(PollingFutureImplWithPoll):
+    def done(self, retry=polling.DEFAULT_RETRY):
+        time.sleep(1)
+        return False
+
+
+def test_result_timeout():
+    future = PollingFutureImplTimeout()
+    with pytest.raises(concurrent.futures.TimeoutError):
+        future.result(timeout=1)
+
+
+def test_exception_timeout():
+    future = PollingFutureImplTimeout()
+    with pytest.raises(concurrent.futures.TimeoutError):
+        future.exception(timeout=1)
+
+
+class PollingFutureImplTransient(PollingFutureImplWithPoll):
+    def __init__(self, errors):
+        super(PollingFutureImplTransient, self).__init__()
+        self._errors = errors
+
+    def done(self, retry=polling.DEFAULT_RETRY):
+        if self._errors:
+            error, self._errors = self._errors[0], self._errors[1:]
+            raise error("testing")
+        self.poll_count += 1
+        self.set_result(42)
+        return True
+
+
+def test_result_transient_error():
+    future = PollingFutureImplTransient(
+        (
+            exceptions.TooManyRequests,
+            exceptions.InternalServerError,
+            exceptions.BadGateway,
+        )
+    )
+    result = future.result()
+    assert result == 42
+    assert future.poll_count == 1
+    # Repeated calls should not cause additional polling
+    assert future.result() == result
+    assert future.poll_count == 1
+
+
+def test_callback_background_thread():
+    future = PollingFutureImplWithPoll()
+    callback = mock.Mock()
+
+    future.add_done_callback(callback)
+
+    assert future._polling_thread is not None
+
+    # Give the thread a second to poll
+    time.sleep(1)
+    assert future.poll_count == 1
+
+    future.event.set()
+    future._polling_thread.join()
+
+    callback.assert_called_once_with(future)
+
+
+def test_double_callback_background_thread():
+    future = PollingFutureImplWithPoll()
+    callback = mock.Mock()
+    callback2 = mock.Mock()
+
+    future.add_done_callback(callback)
+    current_thread = future._polling_thread
+    assert current_thread is not None
+
+    # only one polling thread should be created.
+    future.add_done_callback(callback2)
+    assert future._polling_thread is current_thread
+
+    future.event.set()
+    future._polling_thread.join()
+
+    assert future.poll_count == 1
+    callback.assert_called_once_with(future)
+    callback2.assert_called_once_with(future)
+
+
+class PollingFutureImplWithoutRetry(PollingFutureImpl):
+    def done(self):
+        return True
+
+    def result(self):
+        return super(PollingFutureImplWithoutRetry, self).result()
+
+    def _blocking_poll(self, timeout):
+        return super(PollingFutureImplWithoutRetry, self)._blocking_poll(
+            timeout=timeout
+        )
+
+
+class PollingFutureImplWith_done_or_raise(PollingFutureImpl):
+    def done(self):
+        return True
+
+    def _done_or_raise(self):
+        return super(PollingFutureImplWith_done_or_raise, self)._done_or_raise()
+
+
+def test_polling_future_without_retry():
+    custom_retry = retry.Retry(
+        predicate=retry.if_exception_type(exceptions.TooManyRequests)
+    )
+    future = PollingFutureImplWithoutRetry()
+    assert future.done()
+    assert future.running()
+    assert future.result() is None
+
+    with mock.patch.object(future, "done") as done_mock:
+        future._done_or_raise()
+        done_mock.assert_called_once_with()
+
+    with mock.patch.object(future, "done") as done_mock:
+        future._done_or_raise(retry=custom_retry)
+        done_mock.assert_called_once_with(retry=custom_retry)
+
+
+def test_polling_future_with__done_or_raise():
+    future = PollingFutureImplWith_done_or_raise()
+    assert future.done()
+    assert future.running()
+    assert future.result() is None
diff --git a/tests/unit/gapic/test_client_info.py b/tests/unit/gapic/test_client_info.py
new file mode 100644
index 0000000..2ca5c40
--- /dev/null
+++ b/tests/unit/gapic/test_client_info.py
@@ -0,0 +1,31 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import pytest
+
+try:
+    import grpc  # noqa: F401
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+
+from google.api_core.gapic_v1 import client_info
+
+
+def test_to_grpc_metadata():
+    info = client_info.ClientInfo()
+
+    metadata = info.to_grpc_metadata()
+
+    assert metadata == (client_info.METRICS_METADATA_KEY, info.to_user_agent())
diff --git a/tests/unit/gapic/test_config.py b/tests/unit/gapic/test_config.py
new file mode 100644
index 0000000..5e42fde
--- /dev/null
+++ b/tests/unit/gapic/test_config.py
@@ -0,0 +1,94 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import pytest
+
+try:
+    import grpc  # noqa: F401
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+from google.api_core import exceptions
+from google.api_core.gapic_v1 import config
+
+
+INTERFACE_CONFIG = {
+    "retry_codes": {
+        "idempotent": ["DEADLINE_EXCEEDED", "UNAVAILABLE"],
+        "other": ["FAILED_PRECONDITION"],
+        "non_idempotent": [],
+    },
+    "retry_params": {
+        "default": {
+            "initial_retry_delay_millis": 1000,
+            "retry_delay_multiplier": 2.5,
+            "max_retry_delay_millis": 120000,
+            "initial_rpc_timeout_millis": 120000,
+            "rpc_timeout_multiplier": 1.0,
+            "max_rpc_timeout_millis": 120000,
+            "total_timeout_millis": 600000,
+        },
+        "other": {
+            "initial_retry_delay_millis": 1000,
+            "retry_delay_multiplier": 1,
+            "max_retry_delay_millis": 1000,
+            "initial_rpc_timeout_millis": 1000,
+            "rpc_timeout_multiplier": 1,
+            "max_rpc_timeout_millis": 1000,
+            "total_timeout_millis": 1000,
+        },
+    },
+    "methods": {
+        "AnnotateVideo": {
+            "timeout_millis": 60000,
+            "retry_codes_name": "idempotent",
+            "retry_params_name": "default",
+        },
+        "Other": {
+            "timeout_millis": 60000,
+            "retry_codes_name": "other",
+            "retry_params_name": "other",
+        },
+        "Plain": {"timeout_millis": 30000},
+    },
+}
+
+
+def test_create_method_configs():
+    method_configs = config.parse_method_configs(INTERFACE_CONFIG)
+
+    retry, timeout = method_configs["AnnotateVideo"]
+    assert retry._predicate(exceptions.DeadlineExceeded(None))
+    assert retry._predicate(exceptions.ServiceUnavailable(None))
+    assert retry._initial == 1.0
+    assert retry._multiplier == 2.5
+    assert retry._maximum == 120.0
+    assert retry._deadline == 600.0
+    assert timeout._initial == 120.0
+    assert timeout._multiplier == 1.0
+    assert timeout._maximum == 120.0
+
+    retry, timeout = method_configs["Other"]
+    assert retry._predicate(exceptions.FailedPrecondition(None))
+    assert retry._initial == 1.0
+    assert retry._multiplier == 1.0
+    assert retry._maximum == 1.0
+    assert retry._deadline == 1.0
+    assert timeout._initial == 1.0
+    assert timeout._multiplier == 1.0
+    assert timeout._maximum == 1.0
+
+    retry, timeout = method_configs["Plain"]
+    assert retry is None
+    assert timeout._timeout == 30.0
diff --git a/tests/unit/gapic/test_method.py b/tests/unit/gapic/test_method.py
new file mode 100644
index 0000000..9778d23
--- /dev/null
+++ b/tests/unit/gapic/test_method.py
@@ -0,0 +1,244 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import datetime
+
+import mock
+import pytest
+
+try:
+    import grpc  # noqa: F401
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+
+from google.api_core import exceptions
+from google.api_core import retry
+from google.api_core import timeout
+import google.api_core.gapic_v1.client_info
+import google.api_core.gapic_v1.method
+import google.api_core.page_iterator
+
+
+def _utcnow_monotonic():
+    curr_value = datetime.datetime.min
+    delta = datetime.timedelta(seconds=0.5)
+    while True:
+        yield curr_value
+        curr_value += delta
+
+
+def test__determine_timeout():
+    # Check _determine_timeout always returns a Timeout object.
+    timeout_type_timeout = timeout.ConstantTimeout(600.0)
+    returned_timeout = google.api_core.gapic_v1.method._determine_timeout(
+        600.0, 600.0, None
+    )
+    assert isinstance(returned_timeout, timeout.ConstantTimeout)
+    returned_timeout = google.api_core.gapic_v1.method._determine_timeout(
+        600.0, timeout_type_timeout, None
+    )
+    assert isinstance(returned_timeout, timeout.ConstantTimeout)
+    returned_timeout = google.api_core.gapic_v1.method._determine_timeout(
+        timeout_type_timeout, 600.0, None
+    )
+    assert isinstance(returned_timeout, timeout.ConstantTimeout)
+    returned_timeout = google.api_core.gapic_v1.method._determine_timeout(
+        timeout_type_timeout, timeout_type_timeout, None
+    )
+    assert isinstance(returned_timeout, timeout.ConstantTimeout)
+
+
+def test_wrap_method_basic():
+    method = mock.Mock(spec=["__call__"], return_value=42)
+
+    wrapped_method = google.api_core.gapic_v1.method.wrap_method(method)
+
+    result = wrapped_method(1, 2, meep="moop")
+
+    assert result == 42
+    method.assert_called_once_with(1, 2, meep="moop", metadata=mock.ANY)
+
+    # Check that the default client info was specified in the metadata.
+    metadata = method.call_args[1]["metadata"]
+    assert len(metadata) == 1
+    client_info = google.api_core.gapic_v1.client_info.DEFAULT_CLIENT_INFO
+    user_agent_metadata = client_info.to_grpc_metadata()
+    assert user_agent_metadata in metadata
+
+
+def test_wrap_method_with_no_client_info():
+    method = mock.Mock(spec=["__call__"])
+
+    wrapped_method = google.api_core.gapic_v1.method.wrap_method(
+        method, client_info=None
+    )
+
+    wrapped_method(1, 2, meep="moop")
+
+    method.assert_called_once_with(1, 2, meep="moop")
+
+
+def test_wrap_method_with_custom_client_info():
+    client_info = google.api_core.gapic_v1.client_info.ClientInfo(
+        python_version=1,
+        grpc_version=2,
+        api_core_version=3,
+        gapic_version=4,
+        client_library_version=5,
+    )
+    method = mock.Mock(spec=["__call__"])
+
+    wrapped_method = google.api_core.gapic_v1.method.wrap_method(
+        method, client_info=client_info
+    )
+
+    wrapped_method(1, 2, meep="moop")
+
+    method.assert_called_once_with(1, 2, meep="moop", metadata=mock.ANY)
+
+    # Check that the custom client info was specified in the metadata.
+    metadata = method.call_args[1]["metadata"]
+    assert client_info.to_grpc_metadata() in metadata
+
+
+def test_invoke_wrapped_method_with_metadata():
+    method = mock.Mock(spec=["__call__"])
+
+    wrapped_method = google.api_core.gapic_v1.method.wrap_method(method)
+
+    wrapped_method(mock.sentinel.request, metadata=[("a", "b")])
+
+    method.assert_called_once_with(mock.sentinel.request, metadata=mock.ANY)
+    metadata = method.call_args[1]["metadata"]
+    # Metadata should have two items: the client info metadata and our custom
+    # metadata.
+    assert len(metadata) == 2
+    assert ("a", "b") in metadata
+
+
+def test_invoke_wrapped_method_with_metadata_as_none():
+    method = mock.Mock(spec=["__call__"])
+
+    wrapped_method = google.api_core.gapic_v1.method.wrap_method(method)
+
+    wrapped_method(mock.sentinel.request, metadata=None)
+
+    method.assert_called_once_with(mock.sentinel.request, metadata=mock.ANY)
+    metadata = method.call_args[1]["metadata"]
+    # Metadata should have just one items: the client info metadata.
+    assert len(metadata) == 1
+
+
+@mock.patch("time.sleep")
+def test_wrap_method_with_default_retry_and_timeout(unusued_sleep):
+    method = mock.Mock(
+        spec=["__call__"], side_effect=[exceptions.InternalServerError(None), 42]
+    )
+    default_retry = retry.Retry()
+    default_timeout = timeout.ConstantTimeout(60)
+    wrapped_method = google.api_core.gapic_v1.method.wrap_method(
+        method, default_retry, default_timeout
+    )
+
+    result = wrapped_method()
+
+    assert result == 42
+    assert method.call_count == 2
+    method.assert_called_with(timeout=60, metadata=mock.ANY)
+
+
+@mock.patch("time.sleep")
+def test_wrap_method_with_default_retry_and_timeout_using_sentinel(unusued_sleep):
+    method = mock.Mock(
+        spec=["__call__"], side_effect=[exceptions.InternalServerError(None), 42]
+    )
+    default_retry = retry.Retry()
+    default_timeout = timeout.ConstantTimeout(60)
+    wrapped_method = google.api_core.gapic_v1.method.wrap_method(
+        method, default_retry, default_timeout
+    )
+
+    result = wrapped_method(
+        retry=google.api_core.gapic_v1.method.DEFAULT,
+        timeout=google.api_core.gapic_v1.method.DEFAULT,
+    )
+
+    assert result == 42
+    assert method.call_count == 2
+    method.assert_called_with(timeout=60, metadata=mock.ANY)
+
+
+@mock.patch("time.sleep")
+def test_wrap_method_with_overriding_retry_and_timeout(unusued_sleep):
+    method = mock.Mock(spec=["__call__"], side_effect=[exceptions.NotFound(None), 42])
+    default_retry = retry.Retry()
+    default_timeout = timeout.ConstantTimeout(60)
+    wrapped_method = google.api_core.gapic_v1.method.wrap_method(
+        method, default_retry, default_timeout
+    )
+
+    result = wrapped_method(
+        retry=retry.Retry(retry.if_exception_type(exceptions.NotFound)),
+        timeout=timeout.ConstantTimeout(22),
+    )
+
+    assert result == 42
+    assert method.call_count == 2
+    method.assert_called_with(timeout=22, metadata=mock.ANY)
+
+
+@mock.patch("time.sleep")
+@mock.patch(
+    "google.api_core.datetime_helpers.utcnow",
+    side_effect=_utcnow_monotonic(),
+    autospec=True,
+)
+def test_wrap_method_with_overriding_retry_deadline(utcnow, unused_sleep):
+    method = mock.Mock(
+        spec=["__call__"],
+        side_effect=([exceptions.InternalServerError(None)] * 4) + [42],
+    )
+    default_retry = retry.Retry()
+    default_timeout = timeout.ExponentialTimeout(deadline=60)
+    wrapped_method = google.api_core.gapic_v1.method.wrap_method(
+        method, default_retry, default_timeout
+    )
+
+    # Overriding only the retry's deadline should also override the timeout's
+    # deadline.
+    result = wrapped_method(retry=default_retry.with_deadline(30))
+
+    assert result == 42
+    timeout_args = [call[1]["timeout"] for call in method.call_args_list]
+    assert timeout_args == [5.0, 10.0, 20.0, 26.0, 25.0]
+    assert utcnow.call_count == (
+        1
+        + 5  # First to set the deadline.
+        + 5  # One for each min(timeout, maximum, (DEADLINE - NOW).seconds)
+    )
+
+
+def test_wrap_method_with_overriding_timeout_as_a_number():
+    method = mock.Mock(spec=["__call__"], return_value=42)
+    default_retry = retry.Retry()
+    default_timeout = timeout.ConstantTimeout(60)
+    wrapped_method = google.api_core.gapic_v1.method.wrap_method(
+        method, default_retry, default_timeout
+    )
+
+    result = wrapped_method(timeout=22)
+
+    assert result == 42
+    method.assert_called_once_with(timeout=22, metadata=mock.ANY)
diff --git a/tests/unit/gapic/test_routing_header.py b/tests/unit/gapic/test_routing_header.py
new file mode 100644
index 0000000..3037867
--- /dev/null
+++ b/tests/unit/gapic/test_routing_header.py
@@ -0,0 +1,41 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import pytest
+
+try:
+    import grpc  # noqa: F401
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+
+from google.api_core.gapic_v1 import routing_header
+
+
+def test_to_routing_header():
+    params = [("name", "meep"), ("book.read", "1")]
+    value = routing_header.to_routing_header(params)
+    assert value == "name=meep&book.read=1"
+
+
+def test_to_routing_header_with_slashes():
+    params = [("name", "me/ep"), ("book.read", "1&2")]
+    value = routing_header.to_routing_header(params)
+    assert value == "name=me/ep&book.read=1%262"
+
+
+def test_to_grpc_metadata():
+    params = [("name", "meep"), ("book.read", "1")]
+    metadata = routing_header.to_grpc_metadata(params)
+    assert metadata == (routing_header.ROUTING_METADATA_KEY, "name=meep&book.read=1")
diff --git a/tests/unit/operations_v1/__init__.py b/tests/unit/operations_v1/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/unit/operations_v1/__init__.py
diff --git a/tests/unit/operations_v1/test_operations_client.py b/tests/unit/operations_v1/test_operations_client.py
new file mode 100644
index 0000000..187f0be
--- /dev/null
+++ b/tests/unit/operations_v1/test_operations_client.py
@@ -0,0 +1,98 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import pytest
+
+try:
+    import grpc  # noqa: F401
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+from google.api_core import grpc_helpers
+from google.api_core import operations_v1
+from google.api_core import page_iterator
+from google.longrunning import operations_pb2
+from google.protobuf import empty_pb2
+
+
+def test_get_operation():
+    channel = grpc_helpers.ChannelStub()
+    client = operations_v1.OperationsClient(channel)
+    channel.GetOperation.response = operations_pb2.Operation(name="meep")
+
+    response = client.get_operation("name", metadata=[("header", "foo")])
+
+    assert ("header", "foo") in channel.GetOperation.calls[0].metadata
+    assert ("x-goog-request-params", "name=name") in channel.GetOperation.calls[
+        0
+    ].metadata
+    assert len(channel.GetOperation.requests) == 1
+    assert channel.GetOperation.requests[0].name == "name"
+    assert response == channel.GetOperation.response
+
+
+def test_list_operations():
+    channel = grpc_helpers.ChannelStub()
+    client = operations_v1.OperationsClient(channel)
+    operations = [
+        operations_pb2.Operation(name="1"),
+        operations_pb2.Operation(name="2"),
+    ]
+    list_response = operations_pb2.ListOperationsResponse(operations=operations)
+    channel.ListOperations.response = list_response
+
+    response = client.list_operations("name", "filter", metadata=[("header", "foo")])
+
+    assert isinstance(response, page_iterator.Iterator)
+    assert list(response) == operations
+
+    assert ("header", "foo") in channel.ListOperations.calls[0].metadata
+    assert ("x-goog-request-params", "name=name") in channel.ListOperations.calls[
+        0
+    ].metadata
+    assert len(channel.ListOperations.requests) == 1
+    request = channel.ListOperations.requests[0]
+    assert isinstance(request, operations_pb2.ListOperationsRequest)
+    assert request.name == "name"
+    assert request.filter == "filter"
+
+
+def test_delete_operation():
+    channel = grpc_helpers.ChannelStub()
+    client = operations_v1.OperationsClient(channel)
+    channel.DeleteOperation.response = empty_pb2.Empty()
+
+    client.delete_operation("name", metadata=[("header", "foo")])
+
+    assert ("header", "foo") in channel.DeleteOperation.calls[0].metadata
+    assert ("x-goog-request-params", "name=name") in channel.DeleteOperation.calls[
+        0
+    ].metadata
+    assert len(channel.DeleteOperation.requests) == 1
+    assert channel.DeleteOperation.requests[0].name == "name"
+
+
+def test_cancel_operation():
+    channel = grpc_helpers.ChannelStub()
+    client = operations_v1.OperationsClient(channel)
+    channel.CancelOperation.response = empty_pb2.Empty()
+
+    client.cancel_operation("name", metadata=[("header", "foo")])
+
+    assert ("header", "foo") in channel.CancelOperation.calls[0].metadata
+    assert ("x-goog-request-params", "name=name") in channel.CancelOperation.calls[
+        0
+    ].metadata
+    assert len(channel.CancelOperation.requests) == 1
+    assert channel.CancelOperation.requests[0].name == "name"
diff --git a/tests/unit/operations_v1/test_operations_rest_client.py b/tests/unit/operations_v1/test_operations_rest_client.py
new file mode 100644
index 0000000..dddf6b7
--- /dev/null
+++ b/tests/unit/operations_v1/test_operations_rest_client.py
@@ -0,0 +1,944 @@
+# -*- coding: utf-8 -*-
+# Copyright 2020 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+import os
+
+import mock
+import pytest
+
+try:
+    import grpc  # noqa: F401
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+from requests import Response  # noqa I201
+from requests.sessions import Session
+
+from google.api_core import client_options
+from google.api_core import exceptions as core_exceptions
+from google.api_core import gapic_v1
+from google.api_core.operations_v1 import AbstractOperationsClient
+from google.api_core.operations_v1 import pagers
+from google.api_core.operations_v1 import transports
+import google.auth
+from google.auth import credentials as ga_credentials
+from google.auth.exceptions import MutualTLSChannelError
+from google.longrunning import operations_pb2
+from google.oauth2 import service_account
+from google.protobuf import json_format  # type: ignore
+from google.rpc import status_pb2  # type: ignore
+
+
+HTTP_OPTIONS = {
+    "google.longrunning.Operations.CancelOperation": [
+        {"method": "post", "uri": "/v3/{name=operations/*}:cancel", "body": "*"},
+    ],
+    "google.longrunning.Operations.DeleteOperation": [
+        {"method": "delete", "uri": "/v3/{name=operations/*}"},
+    ],
+    "google.longrunning.Operations.GetOperation": [
+        {"method": "get", "uri": "/v3/{name=operations/*}"},
+    ],
+    "google.longrunning.Operations.ListOperations": [
+        {"method": "get", "uri": "/v3/{name=operations}"},
+    ],
+}
+
+
+def client_cert_source_callback():
+    return b"cert bytes", b"key bytes"
+
+
+def _get_operations_client(http_options=HTTP_OPTIONS):
+    transport = transports.rest.OperationsRestTransport(
+        credentials=ga_credentials.AnonymousCredentials(), http_options=http_options
+    )
+
+    return AbstractOperationsClient(transport=transport)
+
+
+# If default endpoint is localhost, then default mtls endpoint will be the same.
+# This method modifies the default endpoint so the client can produce a different
+# mtls endpoint for endpoint testing purposes.
+def modify_default_endpoint(client):
+    return (
+        "foo.googleapis.com"
+        if ("localhost" in client.DEFAULT_ENDPOINT)
+        else client.DEFAULT_ENDPOINT
+    )
+
+
+def test__get_default_mtls_endpoint():
+    api_endpoint = "example.googleapis.com"
+    api_mtls_endpoint = "example.mtls.googleapis.com"
+    sandbox_endpoint = "example.sandbox.googleapis.com"
+    sandbox_mtls_endpoint = "example.mtls.sandbox.googleapis.com"
+    non_googleapi = "api.example.com"
+
+    assert AbstractOperationsClient._get_default_mtls_endpoint(None) is None
+    assert (
+        AbstractOperationsClient._get_default_mtls_endpoint(api_endpoint)
+        == api_mtls_endpoint
+    )
+    assert (
+        AbstractOperationsClient._get_default_mtls_endpoint(api_mtls_endpoint)
+        == api_mtls_endpoint
+    )
+    assert (
+        AbstractOperationsClient._get_default_mtls_endpoint(sandbox_endpoint)
+        == sandbox_mtls_endpoint
+    )
+    assert (
+        AbstractOperationsClient._get_default_mtls_endpoint(sandbox_mtls_endpoint)
+        == sandbox_mtls_endpoint
+    )
+    assert (
+        AbstractOperationsClient._get_default_mtls_endpoint(non_googleapi)
+        == non_googleapi
+    )
+
+
+@pytest.mark.parametrize("client_class", [AbstractOperationsClient])
+def test_operations_client_from_service_account_info(client_class):
+    creds = ga_credentials.AnonymousCredentials()
+    with mock.patch.object(
+        service_account.Credentials, "from_service_account_info"
+    ) as factory:
+        factory.return_value = creds
+        info = {"valid": True}
+        client = client_class.from_service_account_info(info)
+        assert client.transport._credentials == creds
+        assert isinstance(client, client_class)
+
+        assert client.transport._host == "longrunning.googleapis.com:443"
+
+
+@pytest.mark.parametrize(
+    "transport_class,transport_name", [(transports.OperationsRestTransport, "rest")]
+)
+def test_operations_client_service_account_always_use_jwt(
+    transport_class, transport_name
+):
+    with mock.patch.object(
+        service_account.Credentials, "with_always_use_jwt_access", create=True
+    ) as use_jwt:
+        creds = service_account.Credentials(None, None, None)
+        transport_class(credentials=creds, always_use_jwt_access=True)
+        use_jwt.assert_called_once_with(True)
+
+    with mock.patch.object(
+        service_account.Credentials, "with_always_use_jwt_access", create=True
+    ) as use_jwt:
+        creds = service_account.Credentials(None, None, None)
+        transport_class(credentials=creds, always_use_jwt_access=False)
+        use_jwt.assert_not_called()
+
+
+@pytest.mark.parametrize("client_class", [AbstractOperationsClient])
+def test_operations_client_from_service_account_file(client_class):
+    creds = ga_credentials.AnonymousCredentials()
+    with mock.patch.object(
+        service_account.Credentials, "from_service_account_file"
+    ) as factory:
+        factory.return_value = creds
+        client = client_class.from_service_account_file("dummy/file/path.json")
+        assert client.transport._credentials == creds
+        assert isinstance(client, client_class)
+
+        client = client_class.from_service_account_json("dummy/file/path.json")
+        assert client.transport._credentials == creds
+        assert isinstance(client, client_class)
+
+        assert client.transport._host == "longrunning.googleapis.com:443"
+
+
+def test_operations_client_get_transport_class():
+    transport = AbstractOperationsClient.get_transport_class()
+    available_transports = [
+        transports.OperationsRestTransport,
+    ]
+    assert transport in available_transports
+
+    transport = AbstractOperationsClient.get_transport_class("rest")
+    assert transport == transports.OperationsRestTransport
+
+
+@pytest.mark.parametrize(
+    "client_class,transport_class,transport_name",
+    [(AbstractOperationsClient, transports.OperationsRestTransport, "rest")],
+)
+@mock.patch.object(
+    AbstractOperationsClient,
+    "DEFAULT_ENDPOINT",
+    modify_default_endpoint(AbstractOperationsClient),
+)
+def test_operations_client_client_options(
+    client_class, transport_class, transport_name
+):
+    # Check that if channel is provided we won't create a new one.
+    with mock.patch.object(AbstractOperationsClient, "get_transport_class") as gtc:
+        transport = transport_class(credentials=ga_credentials.AnonymousCredentials())
+        client = client_class(transport=transport)
+        gtc.assert_not_called()
+
+    # Check that if channel is provided via str we will create a new one.
+    with mock.patch.object(AbstractOperationsClient, "get_transport_class") as gtc:
+        client = client_class(transport=transport_name)
+        gtc.assert_called()
+
+    # Check the case api_endpoint is provided.
+    options = client_options.ClientOptions(api_endpoint="squid.clam.whelk")
+    with mock.patch.object(transport_class, "__init__") as patched:
+        patched.return_value = None
+        client = client_class(client_options=options)
+        patched.assert_called_once_with(
+            credentials=None,
+            credentials_file=None,
+            host="squid.clam.whelk",
+            scopes=None,
+            client_cert_source_for_mtls=None,
+            quota_project_id=None,
+            client_info=transports.base.DEFAULT_CLIENT_INFO,
+            always_use_jwt_access=True,
+        )
+
+    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS_ENDPOINT is
+    # "never".
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "never"}):
+        with mock.patch.object(transport_class, "__init__") as patched:
+            patched.return_value = None
+            client = client_class()
+            patched.assert_called_once_with(
+                credentials=None,
+                credentials_file=None,
+                host=client.DEFAULT_ENDPOINT,
+                scopes=None,
+                client_cert_source_for_mtls=None,
+                quota_project_id=None,
+                client_info=transports.base.DEFAULT_CLIENT_INFO,
+                always_use_jwt_access=True,
+            )
+
+    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS_ENDPOINT is
+    # "always".
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "always"}):
+        with mock.patch.object(transport_class, "__init__") as patched:
+            patched.return_value = None
+            client = client_class()
+            patched.assert_called_once_with(
+                credentials=None,
+                credentials_file=None,
+                host=client.DEFAULT_MTLS_ENDPOINT,
+                scopes=None,
+                client_cert_source_for_mtls=None,
+                quota_project_id=None,
+                client_info=transports.base.DEFAULT_CLIENT_INFO,
+                always_use_jwt_access=True,
+            )
+
+    # Check the case api_endpoint is not provided and GOOGLE_API_USE_MTLS_ENDPOINT has
+    # unsupported value.
+    with mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "Unsupported"}):
+        with pytest.raises(MutualTLSChannelError):
+            client = client_class()
+
+    # Check the case GOOGLE_API_USE_CLIENT_CERTIFICATE has unsupported value.
+    with mock.patch.dict(
+        os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": "Unsupported"}
+    ):
+        with pytest.raises(ValueError):
+            client = client_class()
+
+    # Check the case quota_project_id is provided
+    options = client_options.ClientOptions(quota_project_id="octopus")
+    with mock.patch.object(transport_class, "__init__") as patched:
+        patched.return_value = None
+        client = client_class(client_options=options)
+        patched.assert_called_once_with(
+            credentials=None,
+            credentials_file=None,
+            host=client.DEFAULT_ENDPOINT,
+            scopes=None,
+            client_cert_source_for_mtls=None,
+            quota_project_id="octopus",
+            client_info=transports.base.DEFAULT_CLIENT_INFO,
+            always_use_jwt_access=True,
+        )
+
+
+@pytest.mark.parametrize(
+    "client_class,transport_class,transport_name,use_client_cert_env",
+    [
+        (AbstractOperationsClient, transports.OperationsRestTransport, "rest", "true"),
+        (AbstractOperationsClient, transports.OperationsRestTransport, "rest", "false"),
+    ],
+)
+@mock.patch.object(
+    AbstractOperationsClient,
+    "DEFAULT_ENDPOINT",
+    modify_default_endpoint(AbstractOperationsClient),
+)
+@mock.patch.dict(os.environ, {"GOOGLE_API_USE_MTLS_ENDPOINT": "auto"})
+def test_operations_client_mtls_env_auto(
+    client_class, transport_class, transport_name, use_client_cert_env
+):
+    # This tests the endpoint autoswitch behavior. Endpoint is autoswitched to the default
+    # mtls endpoint, if GOOGLE_API_USE_CLIENT_CERTIFICATE is "true" and client cert exists.
+
+    # Check the case client_cert_source is provided. Whether client cert is used depends on
+    # GOOGLE_API_USE_CLIENT_CERTIFICATE value.
+    with mock.patch.dict(
+        os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": use_client_cert_env}
+    ):
+        options = client_options.ClientOptions(
+            client_cert_source=client_cert_source_callback
+        )
+
+        def fake_init(client_cert_source_for_mtls=None, **kwargs):
+            """Invoke client_cert source if provided."""
+
+            if client_cert_source_for_mtls:
+                client_cert_source_for_mtls()
+                return None
+
+        with mock.patch.object(transport_class, "__init__") as patched:
+            patched.side_effect = fake_init
+            client = client_class(client_options=options)
+
+            if use_client_cert_env == "false":
+                expected_client_cert_source = None
+                expected_host = client.DEFAULT_ENDPOINT
+            else:
+                expected_client_cert_source = client_cert_source_callback
+                expected_host = client.DEFAULT_MTLS_ENDPOINT
+
+            patched.assert_called_once_with(
+                credentials=None,
+                credentials_file=None,
+                host=expected_host,
+                scopes=None,
+                client_cert_source_for_mtls=expected_client_cert_source,
+                quota_project_id=None,
+                client_info=transports.base.DEFAULT_CLIENT_INFO,
+                always_use_jwt_access=True,
+            )
+
+    # Check the case ADC client cert is provided. Whether client cert is used depends on
+    # GOOGLE_API_USE_CLIENT_CERTIFICATE value.
+    with mock.patch.dict(
+        os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": use_client_cert_env}
+    ):
+        with mock.patch.object(transport_class, "__init__") as patched:
+            with mock.patch(
+                "google.auth.transport.mtls.has_default_client_cert_source",
+                return_value=True,
+            ):
+                with mock.patch(
+                    "google.auth.transport.mtls.default_client_cert_source",
+                    return_value=client_cert_source_callback,
+                ):
+                    if use_client_cert_env == "false":
+                        expected_host = client.DEFAULT_ENDPOINT
+                        expected_client_cert_source = None
+                    else:
+                        expected_host = client.DEFAULT_MTLS_ENDPOINT
+                        expected_client_cert_source = client_cert_source_callback
+
+                    patched.return_value = None
+                    client = client_class()
+                    patched.assert_called_once_with(
+                        credentials=None,
+                        credentials_file=None,
+                        host=expected_host,
+                        scopes=None,
+                        client_cert_source_for_mtls=expected_client_cert_source,
+                        quota_project_id=None,
+                        client_info=transports.base.DEFAULT_CLIENT_INFO,
+                        always_use_jwt_access=True,
+                    )
+
+    # Check the case client_cert_source and ADC client cert are not provided.
+    with mock.patch.dict(
+        os.environ, {"GOOGLE_API_USE_CLIENT_CERTIFICATE": use_client_cert_env}
+    ):
+        with mock.patch.object(transport_class, "__init__") as patched:
+            with mock.patch(
+                "google.auth.transport.mtls.has_default_client_cert_source",
+                return_value=False,
+            ):
+                patched.return_value = None
+                client = client_class()
+                patched.assert_called_once_with(
+                    credentials=None,
+                    credentials_file=None,
+                    host=client.DEFAULT_ENDPOINT,
+                    scopes=None,
+                    client_cert_source_for_mtls=None,
+                    quota_project_id=None,
+                    client_info=transports.base.DEFAULT_CLIENT_INFO,
+                    always_use_jwt_access=True,
+                )
+
+
+@pytest.mark.parametrize(
+    "client_class,transport_class,transport_name",
+    [(AbstractOperationsClient, transports.OperationsRestTransport, "rest")],
+)
+def test_operations_client_client_options_scopes(
+    client_class, transport_class, transport_name
+):
+    # Check the case scopes are provided.
+    options = client_options.ClientOptions(scopes=["1", "2"],)
+    with mock.patch.object(transport_class, "__init__") as patched:
+        patched.return_value = None
+        client = client_class(client_options=options)
+        patched.assert_called_once_with(
+            credentials=None,
+            credentials_file=None,
+            host=client.DEFAULT_ENDPOINT,
+            scopes=["1", "2"],
+            client_cert_source_for_mtls=None,
+            quota_project_id=None,
+            client_info=transports.base.DEFAULT_CLIENT_INFO,
+            always_use_jwt_access=True,
+        )
+
+
+@pytest.mark.parametrize(
+    "client_class,transport_class,transport_name",
+    [(AbstractOperationsClient, transports.OperationsRestTransport, "rest")],
+)
+def test_operations_client_client_options_credentials_file(
+    client_class, transport_class, transport_name
+):
+    # Check the case credentials file is provided.
+    options = client_options.ClientOptions(credentials_file="credentials.json")
+    with mock.patch.object(transport_class, "__init__") as patched:
+        patched.return_value = None
+        client = client_class(client_options=options)
+        patched.assert_called_once_with(
+            credentials=None,
+            credentials_file="credentials.json",
+            host=client.DEFAULT_ENDPOINT,
+            scopes=None,
+            client_cert_source_for_mtls=None,
+            quota_project_id=None,
+            client_info=transports.base.DEFAULT_CLIENT_INFO,
+            always_use_jwt_access=True,
+        )
+
+
+def test_list_operations_rest(
+    transport: str = "rest", request_type=operations_pb2.ListOperationsRequest
+):
+    client = _get_operations_client()
+
+    # Mock the http request call within the method and fake a response.
+    with mock.patch.object(Session, "request") as req:
+        # Designate an appropriate value for the returned response.
+        return_value = operations_pb2.ListOperationsResponse(
+            next_page_token="next_page_token_value",
+        )
+
+        # Wrap the value into a proper Response obj
+        response_value = Response()
+        response_value.status_code = 200
+        json_return_value = json_format.MessageToJson(return_value)
+        response_value._content = json_return_value.encode("UTF-8")
+        req.return_value = response_value
+        response = client.list_operations(
+            name="operations", filter_="my_filter", page_size=10, page_token="abc"
+        )
+
+        actual_args = req.call_args
+        assert actual_args.args[0] == "GET"
+        assert (
+            actual_args.args[1]
+            == "https://longrunning.googleapis.com:443/v3/operations"
+        )
+        assert actual_args.kwargs["params"] == [
+            ("filter", "my_filter"),
+            ("pageSize", 10),
+            ("pageToken", "abc"),
+        ]
+
+    # Establish that the response is the type that we expect.
+    assert isinstance(response, pagers.ListOperationsPager)
+    assert response.next_page_token == "next_page_token_value"
+
+
+def test_list_operations_rest_failure():
+    client = _get_operations_client(http_options=None)
+
+    with mock.patch.object(Session, "request") as req:
+        response_value = Response()
+        response_value.status_code = 400
+        mock_request = mock.MagicMock()
+        mock_request.method = "GET"
+        mock_request.url = "https://longrunning.googleapis.com:443/v1/operations"
+        response_value.request = mock_request
+        req.return_value = response_value
+        with pytest.raises(core_exceptions.GoogleAPIError):
+            client.list_operations(name="operations")
+
+
+def test_list_operations_rest_pager():
+    client = AbstractOperationsClient(
+        credentials=ga_credentials.AnonymousCredentials(),
+    )
+
+    # Mock the http request call within the method and fake a response.
+    with mock.patch.object(Session, "request") as req:
+        # TODO(kbandes): remove this mock unless there's a good reason for it.
+        # with mock.patch.object(path_template, 'transcode') as transcode:
+        # Set the response as a series of pages
+        response = (
+            operations_pb2.ListOperationsResponse(
+                operations=[
+                    operations_pb2.Operation(),
+                    operations_pb2.Operation(),
+                    operations_pb2.Operation(),
+                ],
+                next_page_token="abc",
+            ),
+            operations_pb2.ListOperationsResponse(
+                operations=[], next_page_token="def",
+            ),
+            operations_pb2.ListOperationsResponse(
+                operations=[operations_pb2.Operation()], next_page_token="ghi",
+            ),
+            operations_pb2.ListOperationsResponse(
+                operations=[operations_pb2.Operation(), operations_pb2.Operation()],
+            ),
+        )
+        # Two responses for two calls
+        response = response + response
+
+        # Wrap the values into proper Response objs
+        response = tuple(json_format.MessageToJson(x) for x in response)
+        return_values = tuple(Response() for i in response)
+        for return_val, response_val in zip(return_values, response):
+            return_val._content = response_val.encode("UTF-8")
+            return_val.status_code = 200
+        req.side_effect = return_values
+
+        pager = client.list_operations(name="operations")
+
+        results = list(pager)
+        assert len(results) == 6
+        assert all(isinstance(i, operations_pb2.Operation) for i in results)
+
+        pages = list(client.list_operations(name="operations").pages)
+        for page_, token in zip(pages, ["abc", "def", "ghi", ""]):
+            assert page_.next_page_token == token
+
+
+def test_get_operation_rest(
+    transport: str = "rest", request_type=operations_pb2.GetOperationRequest
+):
+    client = _get_operations_client()
+
+    # Mock the http request call within the method and fake a response.
+    with mock.patch.object(Session, "request") as req:
+        # Designate an appropriate value for the returned response.
+        return_value = operations_pb2.Operation(
+            name="operations/sample1", done=True, error=status_pb2.Status(code=411),
+        )
+
+        # Wrap the value into a proper Response obj
+        response_value = Response()
+        response_value.status_code = 200
+        json_return_value = json_format.MessageToJson(return_value)
+        response_value._content = json_return_value.encode("UTF-8")
+        req.return_value = response_value
+        response = client.get_operation("operations/sample1")
+
+    actual_args = req.call_args
+    assert actual_args.args[0] == "GET"
+    assert (
+        actual_args.args[1]
+        == "https://longrunning.googleapis.com:443/v3/operations/sample1"
+    )
+
+    # Establish that the response is the type that we expect.
+    assert isinstance(response, operations_pb2.Operation)
+    assert response.name == "operations/sample1"
+    assert response.done is True
+
+
+def test_get_operation_rest_failure():
+    client = _get_operations_client(http_options=None)
+
+    with mock.patch.object(Session, "request") as req:
+        response_value = Response()
+        response_value.status_code = 400
+        mock_request = mock.MagicMock()
+        mock_request.method = "GET"
+        mock_request.url = (
+            "https://longrunning.googleapis.com:443/v1/operations/sample1"
+        )
+        response_value.request = mock_request
+        req.return_value = response_value
+        with pytest.raises(core_exceptions.GoogleAPIError):
+            client.get_operation("operations/sample1")
+
+
+def test_delete_operation_rest(
+    transport: str = "rest", request_type=operations_pb2.DeleteOperationRequest
+):
+    client = _get_operations_client()
+
+    # Mock the http request call within the method and fake a response.
+    with mock.patch.object(Session, "request") as req:
+        # Wrap the value into a proper Response obj
+        response_value = Response()
+        response_value.status_code = 200
+        json_return_value = ""
+        response_value._content = json_return_value.encode("UTF-8")
+        req.return_value = response_value
+        client.delete_operation(name="operations/sample1")
+        assert req.call_count == 1
+        actual_args = req.call_args
+        assert actual_args.args[0] == "DELETE"
+        assert (
+            actual_args.args[1]
+            == "https://longrunning.googleapis.com:443/v3/operations/sample1"
+        )
+
+
+def test_delete_operation_rest_failure():
+    client = _get_operations_client(http_options=None)
+
+    with mock.patch.object(Session, "request") as req:
+        response_value = Response()
+        response_value.status_code = 400
+        mock_request = mock.MagicMock()
+        mock_request.method = "DELETE"
+        mock_request.url = (
+            "https://longrunning.googleapis.com:443/v1/operations/sample1"
+        )
+        response_value.request = mock_request
+        req.return_value = response_value
+        with pytest.raises(core_exceptions.GoogleAPIError):
+            client.delete_operation(name="operations/sample1")
+
+
+def test_cancel_operation_rest(transport: str = "rest"):
+    client = _get_operations_client()
+
+    # Mock the http request call within the method and fake a response.
+    with mock.patch.object(Session, "request") as req:
+        # Wrap the value into a proper Response obj
+        response_value = Response()
+        response_value.status_code = 200
+        json_return_value = ""
+        response_value._content = json_return_value.encode("UTF-8")
+        req.return_value = response_value
+        client.cancel_operation(name="operations/sample1")
+        assert req.call_count == 1
+        actual_args = req.call_args
+        assert actual_args.args[0] == "POST"
+        assert (
+            actual_args.args[1]
+            == "https://longrunning.googleapis.com:443/v3/operations/sample1:cancel"
+        )
+
+
+def test_cancel_operation_rest_failure():
+    client = _get_operations_client(http_options=None)
+
+    with mock.patch.object(Session, "request") as req:
+        response_value = Response()
+        response_value.status_code = 400
+        mock_request = mock.MagicMock()
+        mock_request.method = "POST"
+        mock_request.url = (
+            "https://longrunning.googleapis.com:443/v1/operations/sample1:cancel"
+        )
+        response_value.request = mock_request
+        req.return_value = response_value
+        with pytest.raises(core_exceptions.GoogleAPIError):
+            client.cancel_operation(name="operations/sample1")
+
+
+def test_credentials_transport_error():
+    # It is an error to provide credentials and a transport instance.
+    transport = transports.OperationsRestTransport(
+        credentials=ga_credentials.AnonymousCredentials(),
+    )
+    with pytest.raises(ValueError):
+        AbstractOperationsClient(
+            credentials=ga_credentials.AnonymousCredentials(), transport=transport,
+        )
+
+    # It is an error to provide a credentials file and a transport instance.
+    transport = transports.OperationsRestTransport(
+        credentials=ga_credentials.AnonymousCredentials(),
+    )
+    with pytest.raises(ValueError):
+        AbstractOperationsClient(
+            client_options={"credentials_file": "credentials.json"},
+            transport=transport,
+        )
+
+    # It is an error to provide scopes and a transport instance.
+    transport = transports.OperationsRestTransport(
+        credentials=ga_credentials.AnonymousCredentials(),
+    )
+    with pytest.raises(ValueError):
+        AbstractOperationsClient(
+            client_options={"scopes": ["1", "2"]}, transport=transport,
+        )
+
+
+def test_transport_instance():
+    # A client may be instantiated with a custom transport instance.
+    transport = transports.OperationsRestTransport(
+        credentials=ga_credentials.AnonymousCredentials(),
+    )
+    client = AbstractOperationsClient(transport=transport)
+    assert client.transport is transport
+
+
+@pytest.mark.parametrize("transport_class", [transports.OperationsRestTransport])
+def test_transport_adc(transport_class):
+    # Test default credentials are used if not provided.
+    with mock.patch.object(google.auth, "default") as adc:
+        adc.return_value = (ga_credentials.AnonymousCredentials(), None)
+        transport_class()
+        adc.assert_called_once()
+
+
+def test_operations_base_transport_error():
+    # Passing both a credentials object and credentials_file should raise an error
+    with pytest.raises(core_exceptions.DuplicateCredentialArgs):
+        transports.OperationsTransport(
+            credentials=ga_credentials.AnonymousCredentials(),
+            credentials_file="credentials.json",
+        )
+
+
+def test_operations_base_transport():
+    # Instantiate the base transport.
+    with mock.patch(
+        "google.api_core.operations_v1.transports.OperationsTransport.__init__"
+    ) as Transport:
+        Transport.return_value = None
+        transport = transports.OperationsTransport(
+            credentials=ga_credentials.AnonymousCredentials(),
+        )
+
+    # Every method on the transport should just blindly
+    # raise NotImplementedError.
+    methods = (
+        "list_operations",
+        "get_operation",
+        "delete_operation",
+        "cancel_operation",
+    )
+    for method in methods:
+        with pytest.raises(NotImplementedError):
+            getattr(transport, method)(request=object())
+
+    with pytest.raises(NotImplementedError):
+        transport.close()
+
+
+def test_operations_base_transport_with_credentials_file():
+    # Instantiate the base transport with a credentials file
+    with mock.patch.object(
+        google.auth, "load_credentials_from_file", autospec=True
+    ) as load_creds, mock.patch(
+        "google.api_core.operations_v1.transports.OperationsTransport._prep_wrapped_messages"
+    ) as Transport:
+        Transport.return_value = None
+        load_creds.return_value = (ga_credentials.AnonymousCredentials(), None)
+        transports.OperationsTransport(
+            credentials_file="credentials.json", quota_project_id="octopus",
+        )
+        load_creds.assert_called_once_with(
+            "credentials.json",
+            scopes=None,
+            default_scopes=(),
+            quota_project_id="octopus",
+        )
+
+
+def test_operations_base_transport_with_adc():
+    # Test the default credentials are used if credentials and credentials_file are None.
+    with mock.patch.object(google.auth, "default", autospec=True) as adc, mock.patch(
+        "google.api_core.operations_v1.transports.OperationsTransport._prep_wrapped_messages"
+    ) as Transport:
+        Transport.return_value = None
+        adc.return_value = (ga_credentials.AnonymousCredentials(), None)
+        transports.OperationsTransport()
+        adc.assert_called_once()
+
+
+def test_operations_auth_adc():
+    # If no credentials are provided, we should use ADC credentials.
+    with mock.patch.object(google.auth, "default", autospec=True) as adc:
+        adc.return_value = (ga_credentials.AnonymousCredentials(), None)
+        AbstractOperationsClient()
+        adc.assert_called_once_with(
+            scopes=None, default_scopes=(), quota_project_id=None,
+        )
+
+
+def test_operations_http_transport_client_cert_source_for_mtls():
+    cred = ga_credentials.AnonymousCredentials()
+    with mock.patch(
+        "google.auth.transport.requests.AuthorizedSession.configure_mtls_channel"
+    ) as mock_configure_mtls_channel:
+        transports.OperationsRestTransport(
+            credentials=cred, client_cert_source_for_mtls=client_cert_source_callback
+        )
+        mock_configure_mtls_channel.assert_called_once_with(client_cert_source_callback)
+
+
+def test_operations_host_no_port():
+    client = AbstractOperationsClient(
+        credentials=ga_credentials.AnonymousCredentials(),
+        client_options=client_options.ClientOptions(
+            api_endpoint="longrunning.googleapis.com"
+        ),
+    )
+    assert client.transport._host == "longrunning.googleapis.com:443"
+
+
+def test_operations_host_with_port():
+    client = AbstractOperationsClient(
+        credentials=ga_credentials.AnonymousCredentials(),
+        client_options=client_options.ClientOptions(
+            api_endpoint="longrunning.googleapis.com:8000"
+        ),
+    )
+    assert client.transport._host == "longrunning.googleapis.com:8000"
+
+
+def test_common_billing_account_path():
+    billing_account = "squid"
+    expected = "billingAccounts/{billing_account}".format(
+        billing_account=billing_account,
+    )
+    actual = AbstractOperationsClient.common_billing_account_path(billing_account)
+    assert expected == actual
+
+
+def test_parse_common_billing_account_path():
+    expected = {
+        "billing_account": "clam",
+    }
+    path = AbstractOperationsClient.common_billing_account_path(**expected)
+
+    # Check that the path construction is reversible.
+    actual = AbstractOperationsClient.parse_common_billing_account_path(path)
+    assert expected == actual
+
+
+def test_common_folder_path():
+    folder = "whelk"
+    expected = "folders/{folder}".format(folder=folder,)
+    actual = AbstractOperationsClient.common_folder_path(folder)
+    assert expected == actual
+
+
+def test_parse_common_folder_path():
+    expected = {
+        "folder": "octopus",
+    }
+    path = AbstractOperationsClient.common_folder_path(**expected)
+
+    # Check that the path construction is reversible.
+    actual = AbstractOperationsClient.parse_common_folder_path(path)
+    assert expected == actual
+
+
+def test_common_organization_path():
+    organization = "oyster"
+    expected = "organizations/{organization}".format(organization=organization,)
+    actual = AbstractOperationsClient.common_organization_path(organization)
+    assert expected == actual
+
+
+def test_parse_common_organization_path():
+    expected = {
+        "organization": "nudibranch",
+    }
+    path = AbstractOperationsClient.common_organization_path(**expected)
+
+    # Check that the path construction is reversible.
+    actual = AbstractOperationsClient.parse_common_organization_path(path)
+    assert expected == actual
+
+
+def test_common_project_path():
+    project = "cuttlefish"
+    expected = "projects/{project}".format(project=project,)
+    actual = AbstractOperationsClient.common_project_path(project)
+    assert expected == actual
+
+
+def test_parse_common_project_path():
+    expected = {
+        "project": "mussel",
+    }
+    path = AbstractOperationsClient.common_project_path(**expected)
+
+    # Check that the path construction is reversible.
+    actual = AbstractOperationsClient.parse_common_project_path(path)
+    assert expected == actual
+
+
+def test_common_location_path():
+    project = "winkle"
+    location = "nautilus"
+    expected = "projects/{project}/locations/{location}".format(
+        project=project, location=location,
+    )
+    actual = AbstractOperationsClient.common_location_path(project, location)
+    assert expected == actual
+
+
+def test_parse_common_location_path():
+    expected = {
+        "project": "scallop",
+        "location": "abalone",
+    }
+    path = AbstractOperationsClient.common_location_path(**expected)
+
+    # Check that the path construction is reversible.
+    actual = AbstractOperationsClient.parse_common_location_path(path)
+    assert expected == actual
+
+
+def test_client_withDEFAULT_CLIENT_INFO():
+    client_info = gapic_v1.client_info.ClientInfo()
+
+    with mock.patch.object(
+        transports.OperationsTransport, "_prep_wrapped_messages"
+    ) as prep:
+        AbstractOperationsClient(
+            credentials=ga_credentials.AnonymousCredentials(), client_info=client_info,
+        )
+        prep.assert_called_once_with(client_info)
+
+    with mock.patch.object(
+        transports.OperationsTransport, "_prep_wrapped_messages"
+    ) as prep:
+        transport_class = AbstractOperationsClient.get_transport_class()
+        transport_class(
+            credentials=ga_credentials.AnonymousCredentials(), client_info=client_info,
+        )
+        prep.assert_called_once_with(client_info)
diff --git a/tests/unit/test_bidi.py b/tests/unit/test_bidi.py
new file mode 100644
index 0000000..7fb1620
--- /dev/null
+++ b/tests/unit/test_bidi.py
@@ -0,0 +1,869 @@
+# Copyright 2018, Google LLC All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import datetime
+import logging
+import queue
+import threading
+
+import mock
+import pytest
+
+try:
+    import grpc
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+from google.api_core import bidi
+from google.api_core import exceptions
+
+
+class Test_RequestQueueGenerator(object):
+    def test_bounded_consume(self):
+        call = mock.create_autospec(grpc.Call, instance=True)
+        call.is_active.return_value = True
+
+        def queue_generator(rpc):
+            yield mock.sentinel.A
+            yield queue.Empty()
+            yield mock.sentinel.B
+            rpc.is_active.return_value = False
+            yield mock.sentinel.C
+
+        q = mock.create_autospec(queue.Queue, instance=True)
+        q.get.side_effect = queue_generator(call)
+
+        generator = bidi._RequestQueueGenerator(q)
+        generator.call = call
+
+        items = list(generator)
+
+        assert items == [mock.sentinel.A, mock.sentinel.B]
+
+    def test_yield_initial_and_exit(self):
+        q = mock.create_autospec(queue.Queue, instance=True)
+        q.get.side_effect = queue.Empty()
+        call = mock.create_autospec(grpc.Call, instance=True)
+        call.is_active.return_value = False
+
+        generator = bidi._RequestQueueGenerator(q, initial_request=mock.sentinel.A)
+        generator.call = call
+
+        items = list(generator)
+
+        assert items == [mock.sentinel.A]
+
+    def test_yield_initial_callable_and_exit(self):
+        q = mock.create_autospec(queue.Queue, instance=True)
+        q.get.side_effect = queue.Empty()
+        call = mock.create_autospec(grpc.Call, instance=True)
+        call.is_active.return_value = False
+
+        generator = bidi._RequestQueueGenerator(
+            q, initial_request=lambda: mock.sentinel.A
+        )
+        generator.call = call
+
+        items = list(generator)
+
+        assert items == [mock.sentinel.A]
+
+    def test_exit_when_inactive_with_item(self):
+        q = mock.create_autospec(queue.Queue, instance=True)
+        q.get.side_effect = [mock.sentinel.A, queue.Empty()]
+        call = mock.create_autospec(grpc.Call, instance=True)
+        call.is_active.return_value = False
+
+        generator = bidi._RequestQueueGenerator(q)
+        generator.call = call
+
+        items = list(generator)
+
+        assert items == []
+        # Make sure it put the item back.
+        q.put.assert_called_once_with(mock.sentinel.A)
+
+    def test_exit_when_inactive_empty(self):
+        q = mock.create_autospec(queue.Queue, instance=True)
+        q.get.side_effect = queue.Empty()
+        call = mock.create_autospec(grpc.Call, instance=True)
+        call.is_active.return_value = False
+
+        generator = bidi._RequestQueueGenerator(q)
+        generator.call = call
+
+        items = list(generator)
+
+        assert items == []
+
+    def test_exit_with_stop(self):
+        q = mock.create_autospec(queue.Queue, instance=True)
+        q.get.side_effect = [None, queue.Empty()]
+        call = mock.create_autospec(grpc.Call, instance=True)
+        call.is_active.return_value = True
+
+        generator = bidi._RequestQueueGenerator(q)
+        generator.call = call
+
+        items = list(generator)
+
+        assert items == []
+
+
+class Test_Throttle(object):
+    def test_repr(self):
+        delta = datetime.timedelta(seconds=4.5)
+        instance = bidi._Throttle(access_limit=42, time_window=delta)
+        assert repr(instance) == "_Throttle(access_limit=42, time_window={})".format(
+            repr(delta)
+        )
+
+    def test_raises_error_on_invalid_init_arguments(self):
+        with pytest.raises(ValueError) as exc_info:
+            bidi._Throttle(access_limit=10, time_window=datetime.timedelta(seconds=0.0))
+        assert "time_window" in str(exc_info.value)
+        assert "must be a positive timedelta" in str(exc_info.value)
+
+        with pytest.raises(ValueError) as exc_info:
+            bidi._Throttle(access_limit=0, time_window=datetime.timedelta(seconds=10))
+        assert "access_limit" in str(exc_info.value)
+        assert "must be positive" in str(exc_info.value)
+
+    def test_does_not_delay_entry_attempts_under_threshold(self):
+        throttle = bidi._Throttle(
+            access_limit=3, time_window=datetime.timedelta(seconds=1)
+        )
+        entries = []
+
+        for _ in range(3):
+            with throttle as time_waited:
+                entry_info = {
+                    "entered_at": datetime.datetime.now(),
+                    "reported_wait": time_waited,
+                }
+                entries.append(entry_info)
+
+        # check the reported wait times ...
+        assert all(entry["reported_wait"] == 0.0 for entry in entries)
+
+        # .. and the actual wait times
+        delta = entries[1]["entered_at"] - entries[0]["entered_at"]
+        assert delta.total_seconds() < 0.1
+        delta = entries[2]["entered_at"] - entries[1]["entered_at"]
+        assert delta.total_seconds() < 0.1
+
+    def test_delays_entry_attempts_above_threshold(self):
+        throttle = bidi._Throttle(
+            access_limit=3, time_window=datetime.timedelta(seconds=1)
+        )
+        entries = []
+
+        for _ in range(6):
+            with throttle as time_waited:
+                entry_info = {
+                    "entered_at": datetime.datetime.now(),
+                    "reported_wait": time_waited,
+                }
+                entries.append(entry_info)
+
+        # For each group of 4 consecutive entries the time difference between
+        # the first and the last entry must have been greater than time_window,
+        # because a maximum of 3 are allowed in each time_window.
+        for i, entry in enumerate(entries[3:], start=3):
+            first_entry = entries[i - 3]
+            delta = entry["entered_at"] - first_entry["entered_at"]
+            assert delta.total_seconds() > 1.0
+
+        # check the reported wait times
+        # (NOTE: not using assert all(...), b/c the coverage check would complain)
+        for i, entry in enumerate(entries):
+            if i != 3:
+                assert entry["reported_wait"] == 0.0
+
+        # The delayed entry is expected to have been delayed for a significant
+        # chunk of the full second, and the actual and reported delay times
+        # should reflect that.
+        assert entries[3]["reported_wait"] > 0.7
+        delta = entries[3]["entered_at"] - entries[2]["entered_at"]
+        assert delta.total_seconds() > 0.7
+
+
+class _CallAndFuture(grpc.Call, grpc.Future):
+    pass
+
+
+def make_rpc():
+    """Makes a mock RPC used to test Bidi classes."""
+    call = mock.create_autospec(_CallAndFuture, instance=True)
+    rpc = mock.create_autospec(grpc.StreamStreamMultiCallable, instance=True)
+
+    def rpc_side_effect(request, metadata=None):
+        call.is_active.return_value = True
+        call.request = request
+        call.metadata = metadata
+        return call
+
+    rpc.side_effect = rpc_side_effect
+
+    def cancel_side_effect():
+        call.is_active.return_value = False
+
+    call.cancel.side_effect = cancel_side_effect
+
+    return rpc, call
+
+
+class ClosedCall(object):
+    def __init__(self, exception):
+        self.exception = exception
+
+    def __next__(self):
+        raise self.exception
+
+    def is_active(self):
+        return False
+
+
+class TestBidiRpc(object):
+    def test_initial_state(self):
+        bidi_rpc = bidi.BidiRpc(None)
+
+        assert bidi_rpc.is_active is False
+
+    def test_done_callbacks(self):
+        bidi_rpc = bidi.BidiRpc(None)
+        callback = mock.Mock(spec=["__call__"])
+
+        bidi_rpc.add_done_callback(callback)
+        bidi_rpc._on_call_done(mock.sentinel.future)
+
+        callback.assert_called_once_with(mock.sentinel.future)
+
+    def test_metadata(self):
+        rpc, call = make_rpc()
+        bidi_rpc = bidi.BidiRpc(rpc, metadata=mock.sentinel.A)
+        assert bidi_rpc._rpc_metadata == mock.sentinel.A
+
+        bidi_rpc.open()
+        assert bidi_rpc.call == call
+        assert bidi_rpc.call.metadata == mock.sentinel.A
+
+    def test_open(self):
+        rpc, call = make_rpc()
+        bidi_rpc = bidi.BidiRpc(rpc)
+
+        bidi_rpc.open()
+
+        assert bidi_rpc.call == call
+        assert bidi_rpc.is_active
+        call.add_done_callback.assert_called_once_with(bidi_rpc._on_call_done)
+
+    def test_open_error_already_open(self):
+        rpc, _ = make_rpc()
+        bidi_rpc = bidi.BidiRpc(rpc)
+
+        bidi_rpc.open()
+
+        with pytest.raises(ValueError):
+            bidi_rpc.open()
+
+    def test_close(self):
+        rpc, call = make_rpc()
+        bidi_rpc = bidi.BidiRpc(rpc)
+        bidi_rpc.open()
+
+        bidi_rpc.close()
+
+        call.cancel.assert_called_once()
+        assert bidi_rpc.call == call
+        assert bidi_rpc.is_active is False
+        # ensure the request queue was signaled to stop.
+        assert bidi_rpc.pending_requests == 1
+        assert bidi_rpc._request_queue.get() is None
+
+    def test_close_no_rpc(self):
+        bidi_rpc = bidi.BidiRpc(None)
+        bidi_rpc.close()
+
+    def test_send(self):
+        rpc, call = make_rpc()
+        bidi_rpc = bidi.BidiRpc(rpc)
+        bidi_rpc.open()
+
+        bidi_rpc.send(mock.sentinel.request)
+
+        assert bidi_rpc.pending_requests == 1
+        assert bidi_rpc._request_queue.get() is mock.sentinel.request
+
+    def test_send_not_open(self):
+        rpc, call = make_rpc()
+        bidi_rpc = bidi.BidiRpc(rpc)
+
+        with pytest.raises(ValueError):
+            bidi_rpc.send(mock.sentinel.request)
+
+    def test_send_dead_rpc(self):
+        error = ValueError()
+        bidi_rpc = bidi.BidiRpc(None)
+        bidi_rpc.call = ClosedCall(error)
+
+        with pytest.raises(ValueError) as exc_info:
+            bidi_rpc.send(mock.sentinel.request)
+
+        assert exc_info.value == error
+
+    def test_recv(self):
+        bidi_rpc = bidi.BidiRpc(None)
+        bidi_rpc.call = iter([mock.sentinel.response])
+
+        response = bidi_rpc.recv()
+
+        assert response == mock.sentinel.response
+
+    def test_recv_not_open(self):
+        rpc, call = make_rpc()
+        bidi_rpc = bidi.BidiRpc(rpc)
+
+        with pytest.raises(ValueError):
+            bidi_rpc.recv()
+
+
+class CallStub(object):
+    def __init__(self, values, active=True):
+        self.values = iter(values)
+        self._is_active = active
+        self.cancelled = False
+
+    def __next__(self):
+        item = next(self.values)
+        if isinstance(item, Exception):
+            self._is_active = False
+            raise item
+        return item
+
+    def is_active(self):
+        return self._is_active
+
+    def add_done_callback(self, callback):
+        pass
+
+    def cancel(self):
+        self.cancelled = True
+
+
+class TestResumableBidiRpc(object):
+    def test_ctor_defaults(self):
+        start_rpc = mock.Mock()
+        should_recover = mock.Mock()
+        bidi_rpc = bidi.ResumableBidiRpc(start_rpc, should_recover)
+
+        assert bidi_rpc.is_active is False
+        assert bidi_rpc._finalized is False
+        assert bidi_rpc._start_rpc is start_rpc
+        assert bidi_rpc._should_recover is should_recover
+        assert bidi_rpc._should_terminate is bidi._never_terminate
+        assert bidi_rpc._initial_request is None
+        assert bidi_rpc._rpc_metadata is None
+        assert bidi_rpc._reopen_throttle is None
+
+    def test_ctor_explicit(self):
+        start_rpc = mock.Mock()
+        should_recover = mock.Mock()
+        should_terminate = mock.Mock()
+        initial_request = mock.Mock()
+        metadata = {"x-foo": "bar"}
+        bidi_rpc = bidi.ResumableBidiRpc(
+            start_rpc,
+            should_recover,
+            should_terminate=should_terminate,
+            initial_request=initial_request,
+            metadata=metadata,
+            throttle_reopen=True,
+        )
+
+        assert bidi_rpc.is_active is False
+        assert bidi_rpc._finalized is False
+        assert bidi_rpc._should_recover is should_recover
+        assert bidi_rpc._should_terminate is should_terminate
+        assert bidi_rpc._initial_request is initial_request
+        assert bidi_rpc._rpc_metadata == metadata
+        assert isinstance(bidi_rpc._reopen_throttle, bidi._Throttle)
+
+    def test_done_callbacks_terminate(self):
+        cancellation = mock.Mock()
+        start_rpc = mock.Mock()
+        should_recover = mock.Mock(spec=["__call__"], return_value=True)
+        should_terminate = mock.Mock(spec=["__call__"], return_value=True)
+        bidi_rpc = bidi.ResumableBidiRpc(
+            start_rpc, should_recover, should_terminate=should_terminate
+        )
+        callback = mock.Mock(spec=["__call__"])
+
+        bidi_rpc.add_done_callback(callback)
+        bidi_rpc._on_call_done(cancellation)
+
+        should_terminate.assert_called_once_with(cancellation)
+        should_recover.assert_not_called()
+        callback.assert_called_once_with(cancellation)
+        assert not bidi_rpc.is_active
+
+    def test_done_callbacks_recoverable(self):
+        start_rpc = mock.create_autospec(grpc.StreamStreamMultiCallable, instance=True)
+        should_recover = mock.Mock(spec=["__call__"], return_value=True)
+        bidi_rpc = bidi.ResumableBidiRpc(start_rpc, should_recover)
+        callback = mock.Mock(spec=["__call__"])
+
+        bidi_rpc.add_done_callback(callback)
+        bidi_rpc._on_call_done(mock.sentinel.future)
+
+        callback.assert_not_called()
+        start_rpc.assert_called_once()
+        should_recover.assert_called_once_with(mock.sentinel.future)
+        assert bidi_rpc.is_active
+
+    def test_done_callbacks_non_recoverable(self):
+        start_rpc = mock.create_autospec(grpc.StreamStreamMultiCallable, instance=True)
+        should_recover = mock.Mock(spec=["__call__"], return_value=False)
+        bidi_rpc = bidi.ResumableBidiRpc(start_rpc, should_recover)
+        callback = mock.Mock(spec=["__call__"])
+
+        bidi_rpc.add_done_callback(callback)
+        bidi_rpc._on_call_done(mock.sentinel.future)
+
+        callback.assert_called_once_with(mock.sentinel.future)
+        should_recover.assert_called_once_with(mock.sentinel.future)
+        assert not bidi_rpc.is_active
+
+    def test_send_terminate(self):
+        cancellation = ValueError()
+        call_1 = CallStub([cancellation], active=False)
+        call_2 = CallStub([])
+        start_rpc = mock.create_autospec(
+            grpc.StreamStreamMultiCallable, instance=True, side_effect=[call_1, call_2]
+        )
+        should_recover = mock.Mock(spec=["__call__"], return_value=False)
+        should_terminate = mock.Mock(spec=["__call__"], return_value=True)
+        bidi_rpc = bidi.ResumableBidiRpc(
+            start_rpc, should_recover, should_terminate=should_terminate
+        )
+
+        bidi_rpc.open()
+
+        bidi_rpc.send(mock.sentinel.request)
+
+        assert bidi_rpc.pending_requests == 1
+        assert bidi_rpc._request_queue.get() is None
+
+        should_recover.assert_not_called()
+        should_terminate.assert_called_once_with(cancellation)
+        assert bidi_rpc.call == call_1
+        assert bidi_rpc.is_active is False
+        assert call_1.cancelled is True
+
+    def test_send_recover(self):
+        error = ValueError()
+        call_1 = CallStub([error], active=False)
+        call_2 = CallStub([])
+        start_rpc = mock.create_autospec(
+            grpc.StreamStreamMultiCallable, instance=True, side_effect=[call_1, call_2]
+        )
+        should_recover = mock.Mock(spec=["__call__"], return_value=True)
+        bidi_rpc = bidi.ResumableBidiRpc(start_rpc, should_recover)
+
+        bidi_rpc.open()
+
+        bidi_rpc.send(mock.sentinel.request)
+
+        assert bidi_rpc.pending_requests == 1
+        assert bidi_rpc._request_queue.get() is mock.sentinel.request
+
+        should_recover.assert_called_once_with(error)
+        assert bidi_rpc.call == call_2
+        assert bidi_rpc.is_active is True
+
+    def test_send_failure(self):
+        error = ValueError()
+        call = CallStub([error], active=False)
+        start_rpc = mock.create_autospec(
+            grpc.StreamStreamMultiCallable, instance=True, return_value=call
+        )
+        should_recover = mock.Mock(spec=["__call__"], return_value=False)
+        bidi_rpc = bidi.ResumableBidiRpc(start_rpc, should_recover)
+
+        bidi_rpc.open()
+
+        with pytest.raises(ValueError) as exc_info:
+            bidi_rpc.send(mock.sentinel.request)
+
+        assert exc_info.value == error
+        should_recover.assert_called_once_with(error)
+        assert bidi_rpc.call == call
+        assert bidi_rpc.is_active is False
+        assert call.cancelled is True
+        assert bidi_rpc.pending_requests == 1
+        assert bidi_rpc._request_queue.get() is None
+
+    def test_recv_terminate(self):
+        cancellation = ValueError()
+        call = CallStub([cancellation])
+        start_rpc = mock.create_autospec(
+            grpc.StreamStreamMultiCallable, instance=True, return_value=call
+        )
+        should_recover = mock.Mock(spec=["__call__"], return_value=False)
+        should_terminate = mock.Mock(spec=["__call__"], return_value=True)
+        bidi_rpc = bidi.ResumableBidiRpc(
+            start_rpc, should_recover, should_terminate=should_terminate
+        )
+
+        bidi_rpc.open()
+
+        bidi_rpc.recv()
+
+        should_recover.assert_not_called()
+        should_terminate.assert_called_once_with(cancellation)
+        assert bidi_rpc.call == call
+        assert bidi_rpc.is_active is False
+        assert call.cancelled is True
+
+    def test_recv_recover(self):
+        error = ValueError()
+        call_1 = CallStub([1, error])
+        call_2 = CallStub([2, 3])
+        start_rpc = mock.create_autospec(
+            grpc.StreamStreamMultiCallable, instance=True, side_effect=[call_1, call_2]
+        )
+        should_recover = mock.Mock(spec=["__call__"], return_value=True)
+        bidi_rpc = bidi.ResumableBidiRpc(start_rpc, should_recover)
+
+        bidi_rpc.open()
+
+        values = []
+        for n in range(3):
+            values.append(bidi_rpc.recv())
+
+        assert values == [1, 2, 3]
+        should_recover.assert_called_once_with(error)
+        assert bidi_rpc.call == call_2
+        assert bidi_rpc.is_active is True
+
+    def test_recv_recover_already_recovered(self):
+        call_1 = CallStub([])
+        call_2 = CallStub([])
+        start_rpc = mock.create_autospec(
+            grpc.StreamStreamMultiCallable, instance=True, side_effect=[call_1, call_2]
+        )
+        callback = mock.Mock()
+        callback.return_value = True
+        bidi_rpc = bidi.ResumableBidiRpc(start_rpc, callback)
+
+        bidi_rpc.open()
+
+        bidi_rpc._reopen()
+
+        assert bidi_rpc.call is call_1
+        assert bidi_rpc.is_active is True
+
+    def test_recv_failure(self):
+        error = ValueError()
+        call = CallStub([error])
+        start_rpc = mock.create_autospec(
+            grpc.StreamStreamMultiCallable, instance=True, return_value=call
+        )
+        should_recover = mock.Mock(spec=["__call__"], return_value=False)
+        bidi_rpc = bidi.ResumableBidiRpc(start_rpc, should_recover)
+
+        bidi_rpc.open()
+
+        with pytest.raises(ValueError) as exc_info:
+            bidi_rpc.recv()
+
+        assert exc_info.value == error
+        should_recover.assert_called_once_with(error)
+        assert bidi_rpc.call == call
+        assert bidi_rpc.is_active is False
+        assert call.cancelled is True
+
+    def test_close(self):
+        call = mock.create_autospec(_CallAndFuture, instance=True)
+
+        def cancel_side_effect():
+            call.is_active.return_value = False
+
+        call.cancel.side_effect = cancel_side_effect
+        start_rpc = mock.create_autospec(
+            grpc.StreamStreamMultiCallable, instance=True, return_value=call
+        )
+        should_recover = mock.Mock(spec=["__call__"], return_value=False)
+        bidi_rpc = bidi.ResumableBidiRpc(start_rpc, should_recover)
+        bidi_rpc.open()
+
+        bidi_rpc.close()
+
+        should_recover.assert_not_called()
+        call.cancel.assert_called_once()
+        assert bidi_rpc.call == call
+        assert bidi_rpc.is_active is False
+        # ensure the request queue was signaled to stop.
+        assert bidi_rpc.pending_requests == 1
+        assert bidi_rpc._request_queue.get() is None
+        assert bidi_rpc._finalized
+
+    def test_reopen_failure_on_rpc_restart(self):
+        error1 = ValueError("1")
+        error2 = ValueError("2")
+        call = CallStub([error1])
+        # Invoking start RPC a second time will trigger an error.
+        start_rpc = mock.create_autospec(
+            grpc.StreamStreamMultiCallable, instance=True, side_effect=[call, error2]
+        )
+        should_recover = mock.Mock(spec=["__call__"], return_value=True)
+        callback = mock.Mock(spec=["__call__"])
+
+        bidi_rpc = bidi.ResumableBidiRpc(start_rpc, should_recover)
+        bidi_rpc.add_done_callback(callback)
+
+        bidi_rpc.open()
+
+        with pytest.raises(ValueError) as exc_info:
+            bidi_rpc.recv()
+
+        assert exc_info.value == error2
+        should_recover.assert_called_once_with(error1)
+        assert bidi_rpc.call is None
+        assert bidi_rpc.is_active is False
+        callback.assert_called_once_with(error2)
+
+    def test_using_throttle_on_reopen_requests(self):
+        call = CallStub([])
+        start_rpc = mock.create_autospec(
+            grpc.StreamStreamMultiCallable, instance=True, return_value=call
+        )
+        should_recover = mock.Mock(spec=["__call__"], return_value=True)
+        bidi_rpc = bidi.ResumableBidiRpc(
+            start_rpc, should_recover, throttle_reopen=True
+        )
+
+        patcher = mock.patch.object(bidi_rpc._reopen_throttle.__class__, "__enter__")
+        with patcher as mock_enter:
+            bidi_rpc._reopen()
+
+        mock_enter.assert_called_once()
+
+    def test_send_not_open(self):
+        bidi_rpc = bidi.ResumableBidiRpc(None, lambda _: False)
+
+        with pytest.raises(ValueError):
+            bidi_rpc.send(mock.sentinel.request)
+
+    def test_recv_not_open(self):
+        bidi_rpc = bidi.ResumableBidiRpc(None, lambda _: False)
+
+        with pytest.raises(ValueError):
+            bidi_rpc.recv()
+
+    def test_finalize_idempotent(self):
+        error1 = ValueError("1")
+        error2 = ValueError("2")
+        callback = mock.Mock(spec=["__call__"])
+        should_recover = mock.Mock(spec=["__call__"], return_value=False)
+
+        bidi_rpc = bidi.ResumableBidiRpc(mock.sentinel.start_rpc, should_recover)
+
+        bidi_rpc.add_done_callback(callback)
+
+        bidi_rpc._on_call_done(error1)
+        bidi_rpc._on_call_done(error2)
+
+        callback.assert_called_once_with(error1)
+
+
+class TestBackgroundConsumer(object):
+    def test_consume_once_then_exit(self):
+        bidi_rpc = mock.create_autospec(bidi.BidiRpc, instance=True)
+        bidi_rpc.is_active = True
+        bidi_rpc.recv.side_effect = [mock.sentinel.response_1]
+        recved = threading.Event()
+
+        def on_response(response):
+            assert response == mock.sentinel.response_1
+            bidi_rpc.is_active = False
+            recved.set()
+
+        consumer = bidi.BackgroundConsumer(bidi_rpc, on_response)
+
+        consumer.start()
+
+        recved.wait()
+
+        bidi_rpc.recv.assert_called_once()
+        assert bidi_rpc.is_active is False
+
+        consumer.stop()
+
+        bidi_rpc.close.assert_called_once()
+        assert consumer.is_active is False
+
+    def test_pause_resume_and_close(self):
+        # This test is relatively complex. It attempts to start the consumer,
+        # consume one item, pause the consumer, check the state of the world,
+        # then resume the consumer. Doing this in a deterministic fashion
+        # requires a bit more mocking and patching than usual.
+
+        bidi_rpc = mock.create_autospec(bidi.BidiRpc, instance=True)
+        bidi_rpc.is_active = True
+
+        def close_side_effect():
+            bidi_rpc.is_active = False
+
+        bidi_rpc.close.side_effect = close_side_effect
+
+        # These are used to coordinate the two threads to ensure deterministic
+        # execution.
+        should_continue = threading.Event()
+        responses_and_events = {
+            mock.sentinel.response_1: threading.Event(),
+            mock.sentinel.response_2: threading.Event(),
+        }
+        bidi_rpc.recv.side_effect = [mock.sentinel.response_1, mock.sentinel.response_2]
+
+        recved_responses = []
+        consumer = None
+
+        def on_response(response):
+            if response == mock.sentinel.response_1:
+                consumer.pause()
+
+            recved_responses.append(response)
+            responses_and_events[response].set()
+            should_continue.wait()
+
+        consumer = bidi.BackgroundConsumer(bidi_rpc, on_response)
+
+        consumer.start()
+
+        # Wait for the first response to be recved.
+        responses_and_events[mock.sentinel.response_1].wait()
+
+        # Ensure only one item has been recved and that the consumer is paused.
+        assert recved_responses == [mock.sentinel.response_1]
+        assert consumer.is_paused is True
+        assert consumer.is_active is True
+
+        # Unpause the consumer, wait for the second item, then close the
+        # consumer.
+        should_continue.set()
+        consumer.resume()
+
+        responses_and_events[mock.sentinel.response_2].wait()
+
+        assert recved_responses == [mock.sentinel.response_1, mock.sentinel.response_2]
+
+        consumer.stop()
+
+        assert consumer.is_active is False
+
+    def test_wake_on_error(self):
+        should_continue = threading.Event()
+
+        bidi_rpc = mock.create_autospec(bidi.BidiRpc, instance=True)
+        bidi_rpc.is_active = True
+        bidi_rpc.add_done_callback.side_effect = lambda _: should_continue.set()
+
+        consumer = bidi.BackgroundConsumer(bidi_rpc, mock.sentinel.on_response)
+
+        # Start the consumer paused, which should immediately put it into wait
+        # state.
+        consumer.pause()
+        consumer.start()
+
+        # Wait for add_done_callback to be called
+        should_continue.wait()
+        bidi_rpc.add_done_callback.assert_called_once_with(consumer._on_call_done)
+
+        # The consumer should now be blocked on waiting to be unpaused.
+        assert consumer.is_active
+        assert consumer.is_paused
+
+        # Trigger the done callback, it should unpause the consumer and cause
+        # it to exit.
+        bidi_rpc.is_active = False
+        consumer._on_call_done(bidi_rpc)
+
+        # It may take a few cycles for the thread to exit.
+        while consumer.is_active:
+            pass
+
+    def test_consumer_expected_error(self, caplog):
+        caplog.set_level(logging.DEBUG)
+
+        bidi_rpc = mock.create_autospec(bidi.BidiRpc, instance=True)
+        bidi_rpc.is_active = True
+        bidi_rpc.recv.side_effect = exceptions.ServiceUnavailable("Gone away")
+
+        on_response = mock.Mock(spec=["__call__"])
+
+        consumer = bidi.BackgroundConsumer(bidi_rpc, on_response)
+
+        consumer.start()
+
+        # Wait for the consumer's thread to exit.
+        while consumer.is_active:
+            pass
+
+        on_response.assert_not_called()
+        bidi_rpc.recv.assert_called_once()
+        assert "caught error" in caplog.text
+
+    def test_consumer_unexpected_error(self, caplog):
+        caplog.set_level(logging.DEBUG)
+
+        bidi_rpc = mock.create_autospec(bidi.BidiRpc, instance=True)
+        bidi_rpc.is_active = True
+        bidi_rpc.recv.side_effect = ValueError()
+
+        on_response = mock.Mock(spec=["__call__"])
+
+        consumer = bidi.BackgroundConsumer(bidi_rpc, on_response)
+
+        consumer.start()
+
+        # Wait for the consumer's thread to exit.
+        while consumer.is_active:
+            pass  # pragma: NO COVER (race condition)
+
+        on_response.assert_not_called()
+        bidi_rpc.recv.assert_called_once()
+        assert "caught unexpected exception" in caplog.text
+
+    def test_double_stop(self, caplog):
+        caplog.set_level(logging.DEBUG)
+        bidi_rpc = mock.create_autospec(bidi.BidiRpc, instance=True)
+        bidi_rpc.is_active = True
+        on_response = mock.Mock(spec=["__call__"])
+
+        def close_side_effect():
+            bidi_rpc.is_active = False
+
+        bidi_rpc.close.side_effect = close_side_effect
+
+        consumer = bidi.BackgroundConsumer(bidi_rpc, on_response)
+
+        consumer.start()
+        assert consumer.is_active is True
+
+        consumer.stop()
+        assert consumer.is_active is False
+
+        # calling stop twice should not result in an error.
+        consumer.stop()
diff --git a/tests/unit/test_client_info.py b/tests/unit/test_client_info.py
new file mode 100644
index 0000000..f5eebfb
--- /dev/null
+++ b/tests/unit/test_client_info.py
@@ -0,0 +1,98 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+try:
+    import grpc
+except ImportError:
+    grpc = None
+
+from google.api_core import client_info
+
+
+def test_constructor_defaults():
+    info = client_info.ClientInfo()
+
+    assert info.python_version is not None
+
+    if grpc is not None:
+        assert info.grpc_version is not None
+    else:
+        assert info.grpc_version is None
+
+    assert info.api_core_version is not None
+    assert info.gapic_version is None
+    assert info.client_library_version is None
+    assert info.rest_version is None
+
+
+def test_constructor_options():
+    info = client_info.ClientInfo(
+        python_version="1",
+        grpc_version="2",
+        api_core_version="3",
+        gapic_version="4",
+        client_library_version="5",
+        user_agent="6",
+        rest_version="7",
+    )
+
+    assert info.python_version == "1"
+    assert info.grpc_version == "2"
+    assert info.api_core_version == "3"
+    assert info.gapic_version == "4"
+    assert info.client_library_version == "5"
+    assert info.user_agent == "6"
+    assert info.rest_version == "7"
+
+
+def test_to_user_agent_minimal():
+    info = client_info.ClientInfo(
+        python_version="1", api_core_version="2", grpc_version=None
+    )
+
+    user_agent = info.to_user_agent()
+
+    assert user_agent == "gl-python/1 gax/2"
+
+
+def test_to_user_agent_full():
+    info = client_info.ClientInfo(
+        python_version="1",
+        grpc_version="2",
+        api_core_version="3",
+        gapic_version="4",
+        client_library_version="5",
+        user_agent="app-name/1.0",
+    )
+
+    user_agent = info.to_user_agent()
+
+    assert user_agent == "app-name/1.0 gl-python/1 grpc/2 gax/3 gapic/4 gccl/5"
+
+
+def test_to_user_agent_rest():
+    info = client_info.ClientInfo(
+        python_version="1",
+        grpc_version=None,
+        rest_version="2",
+        api_core_version="3",
+        gapic_version="4",
+        client_library_version="5",
+        user_agent="app-name/1.0",
+    )
+
+    user_agent = info.to_user_agent()
+
+    assert user_agent == "app-name/1.0 gl-python/1 rest/2 gax/3 gapic/4 gccl/5"
diff --git a/tests/unit/test_client_options.py b/tests/unit/test_client_options.py
new file mode 100644
index 0000000..38b9ad0
--- /dev/null
+++ b/tests/unit/test_client_options.py
@@ -0,0 +1,117 @@
+# Copyright 2019 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import pytest
+
+from google.api_core import client_options
+
+
+def get_client_cert():
+    return b"cert", b"key"
+
+
+def get_client_encrypted_cert():
+    return "cert_path", "key_path", b"passphrase"
+
+
+def test_constructor():
+
+    options = client_options.ClientOptions(
+        api_endpoint="foo.googleapis.com",
+        client_cert_source=get_client_cert,
+        quota_project_id="quote-proj",
+        credentials_file="path/to/credentials.json",
+        scopes=[
+            "https://www.googleapis.com/auth/cloud-platform",
+            "https://www.googleapis.com/auth/cloud-platform.read-only",
+        ],
+    )
+
+    assert options.api_endpoint == "foo.googleapis.com"
+    assert options.client_cert_source() == (b"cert", b"key")
+    assert options.quota_project_id == "quote-proj"
+    assert options.credentials_file == "path/to/credentials.json"
+    assert options.scopes == [
+        "https://www.googleapis.com/auth/cloud-platform",
+        "https://www.googleapis.com/auth/cloud-platform.read-only",
+    ]
+
+
+def test_constructor_with_encrypted_cert_source():
+
+    options = client_options.ClientOptions(
+        api_endpoint="foo.googleapis.com",
+        client_encrypted_cert_source=get_client_encrypted_cert,
+    )
+
+    assert options.api_endpoint == "foo.googleapis.com"
+    assert options.client_encrypted_cert_source() == (
+        "cert_path",
+        "key_path",
+        b"passphrase",
+    )
+
+
+def test_constructor_with_both_cert_sources():
+    with pytest.raises(ValueError):
+        client_options.ClientOptions(
+            api_endpoint="foo.googleapis.com",
+            client_cert_source=get_client_cert,
+            client_encrypted_cert_source=get_client_encrypted_cert,
+        )
+
+
+def test_from_dict():
+    options = client_options.from_dict(
+        {
+            "api_endpoint": "foo.googleapis.com",
+            "client_cert_source": get_client_cert,
+            "quota_project_id": "quote-proj",
+            "credentials_file": "path/to/credentials.json",
+            "scopes": [
+                "https://www.googleapis.com/auth/cloud-platform",
+                "https://www.googleapis.com/auth/cloud-platform.read-only",
+            ],
+        }
+    )
+
+    assert options.api_endpoint == "foo.googleapis.com"
+    assert options.client_cert_source() == (b"cert", b"key")
+    assert options.quota_project_id == "quote-proj"
+    assert options.credentials_file == "path/to/credentials.json"
+    assert options.scopes == [
+        "https://www.googleapis.com/auth/cloud-platform",
+        "https://www.googleapis.com/auth/cloud-platform.read-only",
+    ]
+
+
+def test_from_dict_bad_argument():
+    with pytest.raises(ValueError):
+        client_options.from_dict(
+            {
+                "api_endpoint": "foo.googleapis.com",
+                "bad_arg": "1234",
+                "client_cert_source": get_client_cert,
+            }
+        )
+
+
+def test_repr():
+    options = client_options.ClientOptions(api_endpoint="foo.googleapis.com")
+
+    assert (
+        repr(options)
+        == "ClientOptions: {'api_endpoint': 'foo.googleapis.com', 'client_cert_source': None, 'client_encrypted_cert_source': None}"
+        or "ClientOptions: {'client_encrypted_cert_source': None, 'client_cert_source': None, 'api_endpoint': 'foo.googleapis.com'}"
+    )
diff --git a/tests/unit/test_datetime_helpers.py b/tests/unit/test_datetime_helpers.py
new file mode 100644
index 0000000..5f5470a
--- /dev/null
+++ b/tests/unit/test_datetime_helpers.py
@@ -0,0 +1,396 @@
+# Copyright 2017, Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import calendar
+import datetime
+
+import pytest
+
+from google.api_core import datetime_helpers
+from google.protobuf import timestamp_pb2
+
+
+ONE_MINUTE_IN_MICROSECONDS = 60 * 1e6
+
+
+def test_utcnow():
+    result = datetime_helpers.utcnow()
+    assert isinstance(result, datetime.datetime)
+
+
+def test_to_milliseconds():
+    dt = datetime.datetime(1970, 1, 1, 0, 0, 1, tzinfo=datetime.timezone.utc)
+    assert datetime_helpers.to_milliseconds(dt) == 1000
+
+
+def test_to_microseconds():
+    microseconds = 314159
+    dt = datetime.datetime(1970, 1, 1, 0, 0, 0, microsecond=microseconds)
+    assert datetime_helpers.to_microseconds(dt) == microseconds
+
+
+def test_to_microseconds_non_utc():
+    zone = datetime.timezone(datetime.timedelta(minutes=-1))
+    dt = datetime.datetime(1970, 1, 1, 0, 0, 0, tzinfo=zone)
+    assert datetime_helpers.to_microseconds(dt) == ONE_MINUTE_IN_MICROSECONDS
+
+
+def test_to_microseconds_naive():
+    microseconds = 314159
+    dt = datetime.datetime(1970, 1, 1, 0, 0, 0, microsecond=microseconds, tzinfo=None)
+    assert datetime_helpers.to_microseconds(dt) == microseconds
+
+
+def test_from_microseconds():
+    five_mins_from_epoch_in_microseconds = 5 * ONE_MINUTE_IN_MICROSECONDS
+    five_mins_from_epoch_datetime = datetime.datetime(
+        1970, 1, 1, 0, 5, 0, tzinfo=datetime.timezone.utc
+    )
+
+    result = datetime_helpers.from_microseconds(five_mins_from_epoch_in_microseconds)
+
+    assert result == five_mins_from_epoch_datetime
+
+
+def test_from_iso8601_date():
+    today = datetime.date.today()
+    iso_8601_today = today.strftime("%Y-%m-%d")
+
+    assert datetime_helpers.from_iso8601_date(iso_8601_today) == today
+
+
+def test_from_iso8601_time():
+    assert datetime_helpers.from_iso8601_time("12:09:42") == datetime.time(12, 9, 42)
+
+
+def test_from_rfc3339():
+    value = "2009-12-17T12:44:32.123456Z"
+    assert datetime_helpers.from_rfc3339(value) == datetime.datetime(
+        2009, 12, 17, 12, 44, 32, 123456, datetime.timezone.utc
+    )
+
+
+def test_from_rfc3339_nanos():
+    value = "2009-12-17T12:44:32.123456Z"
+    assert datetime_helpers.from_rfc3339_nanos(value) == datetime.datetime(
+        2009, 12, 17, 12, 44, 32, 123456, datetime.timezone.utc
+    )
+
+
+def test_from_rfc3339_without_nanos():
+    value = "2009-12-17T12:44:32Z"
+    assert datetime_helpers.from_rfc3339(value) == datetime.datetime(
+        2009, 12, 17, 12, 44, 32, 0, datetime.timezone.utc
+    )
+
+
+def test_from_rfc3339_nanos_without_nanos():
+    value = "2009-12-17T12:44:32Z"
+    assert datetime_helpers.from_rfc3339_nanos(value) == datetime.datetime(
+        2009, 12, 17, 12, 44, 32, 0, datetime.timezone.utc
+    )
+
+
+@pytest.mark.parametrize(
+    "truncated, micros",
+    [
+        ("12345678", 123456),
+        ("1234567", 123456),
+        ("123456", 123456),
+        ("12345", 123450),
+        ("1234", 123400),
+        ("123", 123000),
+        ("12", 120000),
+        ("1", 100000),
+    ],
+)
+def test_from_rfc3339_with_truncated_nanos(truncated, micros):
+    value = "2009-12-17T12:44:32.{}Z".format(truncated)
+    assert datetime_helpers.from_rfc3339(value) == datetime.datetime(
+        2009, 12, 17, 12, 44, 32, micros, datetime.timezone.utc
+    )
+
+
+def test_from_rfc3339_nanos_is_deprecated():
+    value = "2009-12-17T12:44:32.123456Z"
+
+    result = datetime_helpers.from_rfc3339(value)
+    result_nanos = datetime_helpers.from_rfc3339_nanos(value)
+
+    assert result == result_nanos
+
+
+@pytest.mark.parametrize(
+    "truncated, micros",
+    [
+        ("12345678", 123456),
+        ("1234567", 123456),
+        ("123456", 123456),
+        ("12345", 123450),
+        ("1234", 123400),
+        ("123", 123000),
+        ("12", 120000),
+        ("1", 100000),
+    ],
+)
+def test_from_rfc3339_nanos_with_truncated_nanos(truncated, micros):
+    value = "2009-12-17T12:44:32.{}Z".format(truncated)
+    assert datetime_helpers.from_rfc3339_nanos(value) == datetime.datetime(
+        2009, 12, 17, 12, 44, 32, micros, datetime.timezone.utc
+    )
+
+
+def test_from_rfc3339_wo_nanos_raise_exception():
+    value = "2009-12-17T12:44:32"
+    with pytest.raises(ValueError):
+        datetime_helpers.from_rfc3339(value)
+
+
+def test_from_rfc3339_w_nanos_raise_exception():
+    value = "2009-12-17T12:44:32.123456"
+    with pytest.raises(ValueError):
+        datetime_helpers.from_rfc3339(value)
+
+
+def test_to_rfc3339():
+    value = datetime.datetime(2016, 4, 5, 13, 30, 0)
+    expected = "2016-04-05T13:30:00.000000Z"
+    assert datetime_helpers.to_rfc3339(value) == expected
+
+
+def test_to_rfc3339_with_utc():
+    value = datetime.datetime(2016, 4, 5, 13, 30, 0, tzinfo=datetime.timezone.utc)
+    expected = "2016-04-05T13:30:00.000000Z"
+    assert datetime_helpers.to_rfc3339(value, ignore_zone=False) == expected
+
+
+def test_to_rfc3339_with_non_utc():
+    zone = datetime.timezone(datetime.timedelta(minutes=-60))
+    value = datetime.datetime(2016, 4, 5, 13, 30, 0, tzinfo=zone)
+    expected = "2016-04-05T14:30:00.000000Z"
+    assert datetime_helpers.to_rfc3339(value, ignore_zone=False) == expected
+
+
+def test_to_rfc3339_with_non_utc_ignore_zone():
+    zone = datetime.timezone(datetime.timedelta(minutes=-60))
+    value = datetime.datetime(2016, 4, 5, 13, 30, 0, tzinfo=zone)
+    expected = "2016-04-05T13:30:00.000000Z"
+    assert datetime_helpers.to_rfc3339(value, ignore_zone=True) == expected
+
+
+class Test_DateTimeWithNanos(object):
+    @staticmethod
+    def test_ctor_wo_nanos():
+        stamp = datetime_helpers.DatetimeWithNanoseconds(
+            2016, 12, 20, 21, 13, 47, 123456
+        )
+        assert stamp.year == 2016
+        assert stamp.month == 12
+        assert stamp.day == 20
+        assert stamp.hour == 21
+        assert stamp.minute == 13
+        assert stamp.second == 47
+        assert stamp.microsecond == 123456
+        assert stamp.nanosecond == 0
+
+    @staticmethod
+    def test_ctor_w_nanos():
+        stamp = datetime_helpers.DatetimeWithNanoseconds(
+            2016, 12, 20, 21, 13, 47, nanosecond=123456789
+        )
+        assert stamp.year == 2016
+        assert stamp.month == 12
+        assert stamp.day == 20
+        assert stamp.hour == 21
+        assert stamp.minute == 13
+        assert stamp.second == 47
+        assert stamp.microsecond == 123456
+        assert stamp.nanosecond == 123456789
+
+    @staticmethod
+    def test_ctor_w_micros_positional_and_nanos():
+        with pytest.raises(TypeError):
+            datetime_helpers.DatetimeWithNanoseconds(
+                2016, 12, 20, 21, 13, 47, 123456, nanosecond=123456789
+            )
+
+    @staticmethod
+    def test_ctor_w_micros_keyword_and_nanos():
+        with pytest.raises(TypeError):
+            datetime_helpers.DatetimeWithNanoseconds(
+                2016, 12, 20, 21, 13, 47, microsecond=123456, nanosecond=123456789
+            )
+
+    @staticmethod
+    def test_rfc3339_wo_nanos():
+        stamp = datetime_helpers.DatetimeWithNanoseconds(
+            2016, 12, 20, 21, 13, 47, 123456
+        )
+        assert stamp.rfc3339() == "2016-12-20T21:13:47.123456Z"
+
+    @staticmethod
+    def test_rfc3339_wo_nanos_w_leading_zero():
+        stamp = datetime_helpers.DatetimeWithNanoseconds(2016, 12, 20, 21, 13, 47, 1234)
+        assert stamp.rfc3339() == "2016-12-20T21:13:47.001234Z"
+
+    @staticmethod
+    def test_rfc3339_w_nanos():
+        stamp = datetime_helpers.DatetimeWithNanoseconds(
+            2016, 12, 20, 21, 13, 47, nanosecond=123456789
+        )
+        assert stamp.rfc3339() == "2016-12-20T21:13:47.123456789Z"
+
+    @staticmethod
+    def test_rfc3339_w_nanos_w_leading_zero():
+        stamp = datetime_helpers.DatetimeWithNanoseconds(
+            2016, 12, 20, 21, 13, 47, nanosecond=1234567
+        )
+        assert stamp.rfc3339() == "2016-12-20T21:13:47.001234567Z"
+
+    @staticmethod
+    def test_rfc3339_w_nanos_no_trailing_zeroes():
+        stamp = datetime_helpers.DatetimeWithNanoseconds(
+            2016, 12, 20, 21, 13, 47, nanosecond=100000000
+        )
+        assert stamp.rfc3339() == "2016-12-20T21:13:47.1Z"
+
+    @staticmethod
+    def test_rfc3339_w_nanos_w_leading_zero_and_no_trailing_zeros():
+        stamp = datetime_helpers.DatetimeWithNanoseconds(
+            2016, 12, 20, 21, 13, 47, nanosecond=1234500
+        )
+        assert stamp.rfc3339() == "2016-12-20T21:13:47.0012345Z"
+
+    @staticmethod
+    def test_from_rfc3339_w_invalid():
+        stamp = "2016-12-20T21:13:47"
+        with pytest.raises(ValueError):
+            datetime_helpers.DatetimeWithNanoseconds.from_rfc3339(stamp)
+
+    @staticmethod
+    def test_from_rfc3339_wo_fraction():
+        timestamp = "2016-12-20T21:13:47Z"
+        expected = datetime_helpers.DatetimeWithNanoseconds(
+            2016, 12, 20, 21, 13, 47, tzinfo=datetime.timezone.utc
+        )
+        stamp = datetime_helpers.DatetimeWithNanoseconds.from_rfc3339(timestamp)
+        assert stamp == expected
+
+    @staticmethod
+    def test_from_rfc3339_w_partial_precision():
+        timestamp = "2016-12-20T21:13:47.1Z"
+        expected = datetime_helpers.DatetimeWithNanoseconds(
+            2016, 12, 20, 21, 13, 47, microsecond=100000, tzinfo=datetime.timezone.utc
+        )
+        stamp = datetime_helpers.DatetimeWithNanoseconds.from_rfc3339(timestamp)
+        assert stamp == expected
+
+    @staticmethod
+    def test_from_rfc3339_w_full_precision():
+        timestamp = "2016-12-20T21:13:47.123456789Z"
+        expected = datetime_helpers.DatetimeWithNanoseconds(
+            2016, 12, 20, 21, 13, 47, nanosecond=123456789, tzinfo=datetime.timezone.utc
+        )
+        stamp = datetime_helpers.DatetimeWithNanoseconds.from_rfc3339(timestamp)
+        assert stamp == expected
+
+    @staticmethod
+    @pytest.mark.parametrize(
+        "fractional, nanos",
+        [
+            ("12345678", 123456780),
+            ("1234567", 123456700),
+            ("123456", 123456000),
+            ("12345", 123450000),
+            ("1234", 123400000),
+            ("123", 123000000),
+            ("12", 120000000),
+            ("1", 100000000),
+        ],
+    )
+    def test_from_rfc3339_test_nanoseconds(fractional, nanos):
+        value = "2009-12-17T12:44:32.{}Z".format(fractional)
+        assert (
+            datetime_helpers.DatetimeWithNanoseconds.from_rfc3339(value).nanosecond
+            == nanos
+        )
+
+    @staticmethod
+    def test_timestamp_pb_wo_nanos_naive():
+        stamp = datetime_helpers.DatetimeWithNanoseconds(
+            2016, 12, 20, 21, 13, 47, 123456
+        )
+        delta = (
+            stamp.replace(tzinfo=datetime.timezone.utc) - datetime_helpers._UTC_EPOCH
+        )
+        seconds = int(delta.total_seconds())
+        nanos = 123456000
+        timestamp = timestamp_pb2.Timestamp(seconds=seconds, nanos=nanos)
+        assert stamp.timestamp_pb() == timestamp
+
+    @staticmethod
+    def test_timestamp_pb_w_nanos():
+        stamp = datetime_helpers.DatetimeWithNanoseconds(
+            2016, 12, 20, 21, 13, 47, nanosecond=123456789, tzinfo=datetime.timezone.utc
+        )
+        delta = stamp - datetime_helpers._UTC_EPOCH
+        timestamp = timestamp_pb2.Timestamp(
+            seconds=int(delta.total_seconds()), nanos=123456789
+        )
+        assert stamp.timestamp_pb() == timestamp
+
+    @staticmethod
+    def test_from_timestamp_pb_wo_nanos():
+        when = datetime.datetime(
+            2016, 12, 20, 21, 13, 47, 123456, tzinfo=datetime.timezone.utc
+        )
+        delta = when - datetime_helpers._UTC_EPOCH
+        seconds = int(delta.total_seconds())
+        timestamp = timestamp_pb2.Timestamp(seconds=seconds)
+
+        stamp = datetime_helpers.DatetimeWithNanoseconds.from_timestamp_pb(timestamp)
+
+        assert _to_seconds(when) == _to_seconds(stamp)
+        assert stamp.microsecond == 0
+        assert stamp.nanosecond == 0
+        assert stamp.tzinfo == datetime.timezone.utc
+
+    @staticmethod
+    def test_from_timestamp_pb_w_nanos():
+        when = datetime.datetime(
+            2016, 12, 20, 21, 13, 47, 123456, tzinfo=datetime.timezone.utc
+        )
+        delta = when - datetime_helpers._UTC_EPOCH
+        seconds = int(delta.total_seconds())
+        timestamp = timestamp_pb2.Timestamp(seconds=seconds, nanos=123456789)
+
+        stamp = datetime_helpers.DatetimeWithNanoseconds.from_timestamp_pb(timestamp)
+
+        assert _to_seconds(when) == _to_seconds(stamp)
+        assert stamp.microsecond == 123456
+        assert stamp.nanosecond == 123456789
+        assert stamp.tzinfo == datetime.timezone.utc
+
+
+def _to_seconds(value):
+    """Convert a datetime to seconds since the unix epoch.
+
+    Args:
+        value (datetime.datetime): The datetime to covert.
+
+    Returns:
+        int: Microseconds since the unix epoch.
+    """
+    assert value.tzinfo is datetime.timezone.utc
+    return calendar.timegm(value.timetuple())
diff --git a/tests/unit/test_exceptions.py b/tests/unit/test_exceptions.py
new file mode 100644
index 0000000..622f58a
--- /dev/null
+++ b/tests/unit/test_exceptions.py
@@ -0,0 +1,353 @@
+# Copyright 2014 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import http.client
+import json
+
+import mock
+import pytest
+import requests
+
+try:
+    import grpc
+    from grpc_status import rpc_status
+except ImportError:
+    grpc = rpc_status = None
+
+from google.api_core import exceptions
+from google.protobuf import any_pb2, json_format
+from google.rpc import error_details_pb2, status_pb2
+
+
+def test_create_google_cloud_error():
+    exception = exceptions.GoogleAPICallError("Testing")
+    exception.code = 600
+    assert str(exception) == "600 Testing"
+    assert exception.message == "Testing"
+    assert exception.errors == []
+    assert exception.response is None
+
+
+def test_create_google_cloud_error_with_args():
+    error = {
+        "code": 600,
+        "message": "Testing",
+    }
+    response = mock.sentinel.response
+    exception = exceptions.GoogleAPICallError("Testing", [error], response=response)
+    exception.code = 600
+    assert str(exception) == "600 Testing"
+    assert exception.message == "Testing"
+    assert exception.errors == [error]
+    assert exception.response == response
+
+
+def test_from_http_status():
+    message = "message"
+    exception = exceptions.from_http_status(http.client.NOT_FOUND, message)
+    assert exception.code == http.client.NOT_FOUND
+    assert exception.message == message
+    assert exception.errors == []
+
+
+def test_from_http_status_with_errors_and_response():
+    message = "message"
+    errors = ["1", "2"]
+    response = mock.sentinel.response
+    exception = exceptions.from_http_status(
+        http.client.NOT_FOUND, message, errors=errors, response=response
+    )
+
+    assert isinstance(exception, exceptions.NotFound)
+    assert exception.code == http.client.NOT_FOUND
+    assert exception.message == message
+    assert exception.errors == errors
+    assert exception.response == response
+
+
+def test_from_http_status_unknown_code():
+    message = "message"
+    status_code = 156
+    exception = exceptions.from_http_status(status_code, message)
+    assert exception.code == status_code
+    assert exception.message == message
+
+
+def make_response(content):
+    response = requests.Response()
+    response._content = content
+    response.status_code = http.client.NOT_FOUND
+    response.request = requests.Request(
+        method="POST", url="https://example.com"
+    ).prepare()
+    return response
+
+
+def test_from_http_response_no_content():
+    response = make_response(None)
+
+    exception = exceptions.from_http_response(response)
+
+    assert isinstance(exception, exceptions.NotFound)
+    assert exception.code == http.client.NOT_FOUND
+    assert exception.message == "POST https://example.com/: unknown error"
+    assert exception.response == response
+
+
+def test_from_http_response_text_content():
+    response = make_response(b"message")
+    response.encoding = "UTF8"  # suppress charset_normalizer warning
+
+    exception = exceptions.from_http_response(response)
+
+    assert isinstance(exception, exceptions.NotFound)
+    assert exception.code == http.client.NOT_FOUND
+    assert exception.message == "POST https://example.com/: message"
+
+
+def test_from_http_response_json_content():
+    response = make_response(
+        json.dumps({"error": {"message": "json message", "errors": ["1", "2"]}}).encode(
+            "utf-8"
+        )
+    )
+
+    exception = exceptions.from_http_response(response)
+
+    assert isinstance(exception, exceptions.NotFound)
+    assert exception.code == http.client.NOT_FOUND
+    assert exception.message == "POST https://example.com/: json message"
+    assert exception.errors == ["1", "2"]
+
+
+def test_from_http_response_bad_json_content():
+    response = make_response(json.dumps({"meep": "moop"}).encode("utf-8"))
+
+    exception = exceptions.from_http_response(response)
+
+    assert isinstance(exception, exceptions.NotFound)
+    assert exception.code == http.client.NOT_FOUND
+    assert exception.message == "POST https://example.com/: unknown error"
+
+
+def test_from_http_response_json_unicode_content():
+    response = make_response(
+        json.dumps(
+            {"error": {"message": "\u2019 message", "errors": ["1", "2"]}}
+        ).encode("utf-8")
+    )
+
+    exception = exceptions.from_http_response(response)
+
+    assert isinstance(exception, exceptions.NotFound)
+    assert exception.code == http.client.NOT_FOUND
+    assert exception.message == "POST https://example.com/: \u2019 message"
+    assert exception.errors == ["1", "2"]
+
+
+@pytest.mark.skipif(grpc is None, reason="No grpc")
+def test_from_grpc_status():
+    message = "message"
+    exception = exceptions.from_grpc_status(grpc.StatusCode.OUT_OF_RANGE, message)
+    assert isinstance(exception, exceptions.BadRequest)
+    assert isinstance(exception, exceptions.OutOfRange)
+    assert exception.code == http.client.BAD_REQUEST
+    assert exception.grpc_status_code == grpc.StatusCode.OUT_OF_RANGE
+    assert exception.message == message
+    assert exception.errors == []
+
+
+@pytest.mark.skipif(grpc is None, reason="No grpc")
+def test_from_grpc_status_as_int():
+    message = "message"
+    exception = exceptions.from_grpc_status(11, message)
+    assert isinstance(exception, exceptions.BadRequest)
+    assert isinstance(exception, exceptions.OutOfRange)
+    assert exception.code == http.client.BAD_REQUEST
+    assert exception.grpc_status_code == grpc.StatusCode.OUT_OF_RANGE
+    assert exception.message == message
+    assert exception.errors == []
+
+
+@pytest.mark.skipif(grpc is None, reason="No grpc")
+def test_from_grpc_status_with_errors_and_response():
+    message = "message"
+    response = mock.sentinel.response
+    errors = ["1", "2"]
+    exception = exceptions.from_grpc_status(
+        grpc.StatusCode.OUT_OF_RANGE, message, errors=errors, response=response
+    )
+
+    assert isinstance(exception, exceptions.OutOfRange)
+    assert exception.message == message
+    assert exception.errors == errors
+    assert exception.response == response
+
+
+@pytest.mark.skipif(grpc is None, reason="No grpc")
+def test_from_grpc_status_unknown_code():
+    message = "message"
+    exception = exceptions.from_grpc_status(grpc.StatusCode.OK, message)
+    assert exception.grpc_status_code == grpc.StatusCode.OK
+    assert exception.message == message
+
+
+@pytest.mark.skipif(grpc is None, reason="No grpc")
+def test_from_grpc_error():
+    message = "message"
+    error = mock.create_autospec(grpc.Call, instance=True)
+    error.code.return_value = grpc.StatusCode.INVALID_ARGUMENT
+    error.details.return_value = message
+
+    exception = exceptions.from_grpc_error(error)
+
+    assert isinstance(exception, exceptions.BadRequest)
+    assert isinstance(exception, exceptions.InvalidArgument)
+    assert exception.code == http.client.BAD_REQUEST
+    assert exception.grpc_status_code == grpc.StatusCode.INVALID_ARGUMENT
+    assert exception.message == message
+    assert exception.errors == [error]
+    assert exception.response == error
+
+
+@pytest.mark.skipif(grpc is None, reason="No grpc")
+def test_from_grpc_error_non_call():
+    message = "message"
+    error = mock.create_autospec(grpc.RpcError, instance=True)
+    error.__str__.return_value = message
+
+    exception = exceptions.from_grpc_error(error)
+
+    assert isinstance(exception, exceptions.GoogleAPICallError)
+    assert exception.code is None
+    assert exception.grpc_status_code is None
+    assert exception.message == message
+    assert exception.errors == [error]
+    assert exception.response == error
+
+
+@pytest.mark.skipif(grpc is None, reason="No grpc")
+def test_from_grpc_error_bare_call():
+    message = "Testing"
+
+    class TestingError(grpc.Call, grpc.RpcError):
+        def __init__(self, exception):
+            self.exception = exception
+
+        def code(self):
+            return self.exception.grpc_status_code
+
+        def details(self):
+            return message
+
+    nested_message = "message"
+    error = TestingError(exceptions.GoogleAPICallError(nested_message))
+
+    exception = exceptions.from_grpc_error(error)
+
+    assert isinstance(exception, exceptions.GoogleAPICallError)
+    assert exception.code is None
+    assert exception.grpc_status_code is None
+    assert exception.message == message
+    assert exception.errors == [error]
+    assert exception.response == error
+    assert exception.details == []
+
+
+def create_bad_request_details():
+    bad_request_details = error_details_pb2.BadRequest()
+    field_violation = bad_request_details.field_violations.add()
+    field_violation.field = "document.content"
+    field_violation.description = "Must have some text content to annotate."
+    status_detail = any_pb2.Any()
+    status_detail.Pack(bad_request_details)
+    return status_detail
+
+
+def test_error_details_from_rest_response():
+    bad_request_detail = create_bad_request_details()
+    status = status_pb2.Status()
+    status.code = 3
+    status.message = (
+        "3 INVALID_ARGUMENT: One of content, or gcs_content_uri must be set."
+    )
+    status.details.append(bad_request_detail)
+
+    # See JSON schema in https://cloud.google.com/apis/design/errors#http_mapping
+    http_response = make_response(
+        json.dumps({"error": json.loads(json_format.MessageToJson(status))}).encode(
+            "utf-8"
+        )
+    )
+    exception = exceptions.from_http_response(http_response)
+    want_error_details = [json.loads(json_format.MessageToJson(bad_request_detail))]
+    assert want_error_details == exception.details
+    # 404 POST comes from make_response.
+    assert str(exception) == (
+        "404 POST https://example.com/: 3 INVALID_ARGUMENT:"
+        " One of content, or gcs_content_uri must be set."
+        " [{'@type': 'type.googleapis.com/google.rpc.BadRequest',"
+        " 'fieldViolations': [{'field': 'document.content',"
+        " 'description': 'Must have some text content to annotate.'}]}]"
+    )
+
+
+def test_error_details_from_v1_rest_response():
+    response = make_response(
+        json.dumps(
+            {"error": {"message": "\u2019 message", "errors": ["1", "2"]}}
+        ).encode("utf-8")
+    )
+    exception = exceptions.from_http_response(response)
+    assert exception.details == []
+
+
+@pytest.mark.skipif(grpc is None, reason="gRPC not importable")
+def test_error_details_from_grpc_response():
+    status = rpc_status.status_pb2.Status()
+    status.code = 3
+    status.message = (
+        "3 INVALID_ARGUMENT: One of content, or gcs_content_uri must be set."
+    )
+    status_detail = create_bad_request_details()
+    status.details.append(status_detail)
+
+    # Actualy error doesn't matter as long as its grpc.Call,
+    # because from_call is mocked.
+    error = mock.create_autospec(grpc.Call, instance=True)
+    with mock.patch("grpc_status.rpc_status.from_call") as m:
+        m.return_value = status
+        exception = exceptions.from_grpc_error(error)
+
+    bad_request_detail = error_details_pb2.BadRequest()
+    status_detail.Unpack(bad_request_detail)
+    assert exception.details == [bad_request_detail]
+
+
+@pytest.mark.skipif(grpc is None, reason="gRPC not importable")
+def test_error_details_from_grpc_response_unknown_error():
+    status_detail = any_pb2.Any()
+
+    status = rpc_status.status_pb2.Status()
+    status.code = 3
+    status.message = (
+        "3 INVALID_ARGUMENT: One of content, or gcs_content_uri must be set."
+    )
+    status.details.append(status_detail)
+
+    error = mock.create_autospec(grpc.Call, instance=True)
+    with mock.patch("grpc_status.rpc_status.from_call") as m:
+        m.return_value = status
+        exception = exceptions.from_grpc_error(error)
+    assert exception.details == [status_detail]
diff --git a/tests/unit/test_grpc_helpers.py b/tests/unit/test_grpc_helpers.py
new file mode 100644
index 0000000..ca969e4
--- /dev/null
+++ b/tests/unit/test_grpc_helpers.py
@@ -0,0 +1,860 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import mock
+import pytest
+
+try:
+    import grpc
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+from google.api_core import exceptions
+from google.api_core import grpc_helpers
+import google.auth.credentials
+from google.longrunning import operations_pb2
+
+
+def test__patch_callable_name():
+    callable = mock.Mock(spec=["__class__"])
+    callable.__class__ = mock.Mock(spec=["__name__"])
+    callable.__class__.__name__ = "TestCallable"
+
+    grpc_helpers._patch_callable_name(callable)
+
+    assert callable.__name__ == "TestCallable"
+
+
+def test__patch_callable_name_no_op():
+    callable = mock.Mock(spec=["__name__"])
+    callable.__name__ = "test_callable"
+
+    grpc_helpers._patch_callable_name(callable)
+
+    assert callable.__name__ == "test_callable"
+
+
+class RpcErrorImpl(grpc.RpcError, grpc.Call):
+    def __init__(self, code):
+        super(RpcErrorImpl, self).__init__()
+        self._code = code
+
+    def code(self):
+        return self._code
+
+    def details(self):
+        return None
+
+    def trailing_metadata(self):
+        return None
+
+
+def test_wrap_unary_errors():
+    grpc_error = RpcErrorImpl(grpc.StatusCode.INVALID_ARGUMENT)
+    callable_ = mock.Mock(spec=["__call__"], side_effect=grpc_error)
+
+    wrapped_callable = grpc_helpers._wrap_unary_errors(callable_)
+
+    with pytest.raises(exceptions.InvalidArgument) as exc_info:
+        wrapped_callable(1, 2, three="four")
+
+    callable_.assert_called_once_with(1, 2, three="four")
+    assert exc_info.value.response == grpc_error
+
+
+class Test_StreamingResponseIterator:
+    @staticmethod
+    def _make_wrapped(*items):
+        return iter(items)
+
+    @staticmethod
+    def _make_one(wrapped, **kw):
+        return grpc_helpers._StreamingResponseIterator(wrapped, **kw)
+
+    def test_ctor_defaults(self):
+        wrapped = self._make_wrapped("a", "b", "c")
+        iterator = self._make_one(wrapped)
+        assert iterator._stored_first_result == "a"
+        assert list(wrapped) == ["b", "c"]
+
+    def test_ctor_explicit(self):
+        wrapped = self._make_wrapped("a", "b", "c")
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+        assert getattr(iterator, "_stored_first_result", self) is self
+        assert list(wrapped) == ["a", "b", "c"]
+
+    def test_ctor_w_rpc_error_on_prefetch(self):
+        wrapped = mock.MagicMock()
+        wrapped.__next__.side_effect = grpc.RpcError()
+
+        with pytest.raises(grpc.RpcError):
+            self._make_one(wrapped)
+
+    def test___iter__(self):
+        wrapped = self._make_wrapped("a", "b", "c")
+        iterator = self._make_one(wrapped)
+        assert iter(iterator) is iterator
+
+    def test___next___w_cached_first_result(self):
+        wrapped = self._make_wrapped("a", "b", "c")
+        iterator = self._make_one(wrapped)
+        assert next(iterator) == "a"
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+        assert next(iterator) == "b"
+        assert next(iterator) == "c"
+
+    def test___next___wo_cached_first_result(self):
+        wrapped = self._make_wrapped("a", "b", "c")
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+        assert next(iterator) == "a"
+        assert next(iterator) == "b"
+        assert next(iterator) == "c"
+
+    def test___next___w_rpc_error(self):
+        wrapped = mock.MagicMock()
+        wrapped.__next__.side_effect = grpc.RpcError()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        with pytest.raises(exceptions.GoogleAPICallError):
+            next(iterator)
+
+    def test_add_callback(self):
+        wrapped = mock.MagicMock()
+        callback = mock.Mock(spec={})
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.add_callback(callback) is wrapped.add_callback.return_value
+
+        wrapped.add_callback.assert_called_once_with(callback)
+
+    def test_cancel(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.cancel() is wrapped.cancel.return_value
+
+        wrapped.cancel.assert_called_once_with()
+
+    def test_code(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.code() is wrapped.code.return_value
+
+        wrapped.code.assert_called_once_with()
+
+    def test_details(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.details() is wrapped.details.return_value
+
+        wrapped.details.assert_called_once_with()
+
+    def test_initial_metadata(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.initial_metadata() is wrapped.initial_metadata.return_value
+
+        wrapped.initial_metadata.assert_called_once_with()
+
+    def test_is_active(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.is_active() is wrapped.is_active.return_value
+
+        wrapped.is_active.assert_called_once_with()
+
+    def test_time_remaining(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.time_remaining() is wrapped.time_remaining.return_value
+
+        wrapped.time_remaining.assert_called_once_with()
+
+    def test_trailing_metadata(self):
+        wrapped = mock.MagicMock()
+        iterator = self._make_one(wrapped, prefetch_first_result=False)
+
+        assert iterator.trailing_metadata() is wrapped.trailing_metadata.return_value
+
+        wrapped.trailing_metadata.assert_called_once_with()
+
+
+def test_wrap_stream_okay():
+    expected_responses = [1, 2, 3]
+    callable_ = mock.Mock(spec=["__call__"], return_value=iter(expected_responses))
+
+    wrapped_callable = grpc_helpers._wrap_stream_errors(callable_)
+
+    got_iterator = wrapped_callable(1, 2, three="four")
+
+    responses = list(got_iterator)
+
+    callable_.assert_called_once_with(1, 2, three="four")
+    assert responses == expected_responses
+
+
+def test_wrap_stream_prefetch_disabled():
+    responses = [1, 2, 3]
+    iter_responses = iter(responses)
+    callable_ = mock.Mock(spec=["__call__"], return_value=iter_responses)
+    callable_._prefetch_first_result_ = False
+
+    wrapped_callable = grpc_helpers._wrap_stream_errors(callable_)
+    wrapped_callable(1, 2, three="four")
+
+    assert list(iter_responses) == responses  # no items should have been pre-fetched
+    callable_.assert_called_once_with(1, 2, three="four")
+
+
+def test_wrap_stream_iterable_iterface():
+    response_iter = mock.create_autospec(grpc.Call, instance=True)
+    callable_ = mock.Mock(spec=["__call__"], return_value=response_iter)
+
+    wrapped_callable = grpc_helpers._wrap_stream_errors(callable_)
+
+    got_iterator = wrapped_callable()
+
+    callable_.assert_called_once_with()
+
+    # Check each aliased method in the grpc.Call interface
+    got_iterator.add_callback(mock.sentinel.callback)
+    response_iter.add_callback.assert_called_once_with(mock.sentinel.callback)
+
+    got_iterator.cancel()
+    response_iter.cancel.assert_called_once_with()
+
+    got_iterator.code()
+    response_iter.code.assert_called_once_with()
+
+    got_iterator.details()
+    response_iter.details.assert_called_once_with()
+
+    got_iterator.initial_metadata()
+    response_iter.initial_metadata.assert_called_once_with()
+
+    got_iterator.is_active()
+    response_iter.is_active.assert_called_once_with()
+
+    got_iterator.time_remaining()
+    response_iter.time_remaining.assert_called_once_with()
+
+    got_iterator.trailing_metadata()
+    response_iter.trailing_metadata.assert_called_once_with()
+
+
+def test_wrap_stream_errors_invocation():
+    grpc_error = RpcErrorImpl(grpc.StatusCode.INVALID_ARGUMENT)
+    callable_ = mock.Mock(spec=["__call__"], side_effect=grpc_error)
+
+    wrapped_callable = grpc_helpers._wrap_stream_errors(callable_)
+
+    with pytest.raises(exceptions.InvalidArgument) as exc_info:
+        wrapped_callable(1, 2, three="four")
+
+    callable_.assert_called_once_with(1, 2, three="four")
+    assert exc_info.value.response == grpc_error
+
+
+def test_wrap_stream_empty_iterator():
+    expected_responses = []
+    callable_ = mock.Mock(spec=["__call__"], return_value=iter(expected_responses))
+
+    wrapped_callable = grpc_helpers._wrap_stream_errors(callable_)
+
+    got_iterator = wrapped_callable()
+
+    responses = list(got_iterator)
+
+    callable_.assert_called_once_with()
+    assert responses == expected_responses
+
+
+class RpcResponseIteratorImpl(object):
+    def __init__(self, iterable):
+        self._iterable = iter(iterable)
+
+    def next(self):
+        next_item = next(self._iterable)
+        if isinstance(next_item, RpcErrorImpl):
+            raise next_item
+        return next_item
+
+    __next__ = next
+
+
+def test_wrap_stream_errors_iterator_initialization():
+    grpc_error = RpcErrorImpl(grpc.StatusCode.UNAVAILABLE)
+    response_iter = RpcResponseIteratorImpl([grpc_error])
+    callable_ = mock.Mock(spec=["__call__"], return_value=response_iter)
+
+    wrapped_callable = grpc_helpers._wrap_stream_errors(callable_)
+
+    with pytest.raises(exceptions.ServiceUnavailable) as exc_info:
+        wrapped_callable(1, 2, three="four")
+
+    callable_.assert_called_once_with(1, 2, three="four")
+    assert exc_info.value.response == grpc_error
+
+
+def test_wrap_stream_errors_during_iteration():
+    grpc_error = RpcErrorImpl(grpc.StatusCode.UNAVAILABLE)
+    response_iter = RpcResponseIteratorImpl([1, grpc_error])
+    callable_ = mock.Mock(spec=["__call__"], return_value=response_iter)
+
+    wrapped_callable = grpc_helpers._wrap_stream_errors(callable_)
+    got_iterator = wrapped_callable(1, 2, three="four")
+    next(got_iterator)
+
+    with pytest.raises(exceptions.ServiceUnavailable) as exc_info:
+        next(got_iterator)
+
+    callable_.assert_called_once_with(1, 2, three="four")
+    assert exc_info.value.response == grpc_error
+
+
+@mock.patch("google.api_core.grpc_helpers._wrap_unary_errors")
+def test_wrap_errors_non_streaming(wrap_unary_errors):
+    callable_ = mock.create_autospec(grpc.UnaryUnaryMultiCallable)
+
+    result = grpc_helpers.wrap_errors(callable_)
+
+    assert result == wrap_unary_errors.return_value
+    wrap_unary_errors.assert_called_once_with(callable_)
+
+
+@mock.patch("google.api_core.grpc_helpers._wrap_stream_errors")
+def test_wrap_errors_streaming(wrap_stream_errors):
+    callable_ = mock.create_autospec(grpc.UnaryStreamMultiCallable)
+
+    result = grpc_helpers.wrap_errors(callable_)
+
+    assert result == wrap_stream_errors.return_value
+    wrap_stream_errors.assert_called_once_with(callable_)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch(
+    "google.auth.default",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.projet),
+)
+@mock.patch("grpc.secure_channel")
+def test_create_channel_implicit(grpc_secure_channel, default, composite_creds_call):
+    target = "example.com:443"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers.create_channel(target)
+
+    assert channel is grpc_secure_channel.return_value
+
+    default.assert_called_once_with(scopes=None, default_scopes=None)
+
+    if grpc_helpers.HAS_GRPC_GCP:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds, None)
+    else:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("google.auth.transport.grpc.AuthMetadataPlugin", autospec=True)
+@mock.patch(
+    "google.auth.transport.requests.Request",
+    autospec=True,
+    return_value=mock.sentinel.Request,
+)
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch(
+    "google.auth.default",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.project),
+)
+@mock.patch("grpc.secure_channel")
+def test_create_channel_implicit_with_default_host(
+    grpc_secure_channel, default, composite_creds_call, request, auth_metadata_plugin
+):
+    target = "example.com:443"
+    default_host = "example.com"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers.create_channel(target, default_host=default_host)
+
+    assert channel is grpc_secure_channel.return_value
+
+    default.assert_called_once_with(scopes=None, default_scopes=None)
+    auth_metadata_plugin.assert_called_once_with(
+        mock.sentinel.credentials, mock.sentinel.Request, default_host=default_host
+    )
+
+    if grpc_helpers.HAS_GRPC_GCP:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds, None)
+    else:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch(
+    "google.auth.default",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.projet),
+)
+@mock.patch("grpc.secure_channel")
+def test_create_channel_implicit_with_ssl_creds(
+    grpc_secure_channel, default, composite_creds_call
+):
+    target = "example.com:443"
+
+    ssl_creds = grpc.ssl_channel_credentials()
+
+    grpc_helpers.create_channel(target, ssl_credentials=ssl_creds)
+
+    default.assert_called_once_with(scopes=None, default_scopes=None)
+
+    composite_creds_call.assert_called_once_with(ssl_creds, mock.ANY)
+    composite_creds = composite_creds_call.return_value
+    if grpc_helpers.HAS_GRPC_GCP:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds, None)
+    else:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch(
+    "google.auth.default",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.projet),
+)
+@mock.patch("grpc.secure_channel")
+def test_create_channel_implicit_with_scopes(
+    grpc_secure_channel, default, composite_creds_call
+):
+    target = "example.com:443"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers.create_channel(target, scopes=["one", "two"])
+
+    assert channel is grpc_secure_channel.return_value
+
+    default.assert_called_once_with(scopes=["one", "two"], default_scopes=None)
+
+    if grpc_helpers.HAS_GRPC_GCP:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds, None)
+    else:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch(
+    "google.auth.default",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.projet),
+)
+@mock.patch("grpc.secure_channel")
+def test_create_channel_implicit_with_default_scopes(
+    grpc_secure_channel, default, composite_creds_call
+):
+    target = "example.com:443"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers.create_channel(target, default_scopes=["three", "four"])
+
+    assert channel is grpc_secure_channel.return_value
+
+    default.assert_called_once_with(scopes=None, default_scopes=["three", "four"])
+
+    if grpc_helpers.HAS_GRPC_GCP:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds, None)
+    else:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+def test_create_channel_explicit_with_duplicate_credentials():
+    target = "example.com:443"
+
+    with pytest.raises(exceptions.DuplicateCredentialArgs):
+        grpc_helpers.create_channel(
+            target,
+            credentials_file="credentials.json",
+            credentials=mock.sentinel.credentials,
+        )
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("google.auth.credentials.with_scopes_if_required", autospec=True)
+@mock.patch("grpc.secure_channel")
+def test_create_channel_explicit(grpc_secure_channel, auth_creds, composite_creds_call):
+    target = "example.com:443"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers.create_channel(target, credentials=mock.sentinel.credentials)
+
+    auth_creds.assert_called_once_with(
+        mock.sentinel.credentials, scopes=None, default_scopes=None
+    )
+
+    assert channel is grpc_secure_channel.return_value
+    if grpc_helpers.HAS_GRPC_GCP:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds, None)
+    else:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("grpc.secure_channel")
+def test_create_channel_explicit_scoped(grpc_secure_channel, composite_creds_call):
+    target = "example.com:443"
+    scopes = ["1", "2"]
+    composite_creds = composite_creds_call.return_value
+
+    credentials = mock.create_autospec(google.auth.credentials.Scoped, instance=True)
+    credentials.requires_scopes = True
+
+    channel = grpc_helpers.create_channel(
+        target, credentials=credentials, scopes=scopes
+    )
+
+    credentials.with_scopes.assert_called_once_with(scopes, default_scopes=None)
+
+    assert channel is grpc_secure_channel.return_value
+    if grpc_helpers.HAS_GRPC_GCP:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds, None)
+    else:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("grpc.secure_channel")
+def test_create_channel_explicit_default_scopes(
+    grpc_secure_channel, composite_creds_call
+):
+    target = "example.com:443"
+    default_scopes = ["3", "4"]
+    composite_creds = composite_creds_call.return_value
+
+    credentials = mock.create_autospec(google.auth.credentials.Scoped, instance=True)
+    credentials.requires_scopes = True
+
+    channel = grpc_helpers.create_channel(
+        target, credentials=credentials, default_scopes=default_scopes
+    )
+
+    credentials.with_scopes.assert_called_once_with(
+        scopes=None, default_scopes=default_scopes
+    )
+
+    assert channel is grpc_secure_channel.return_value
+    if grpc_helpers.HAS_GRPC_GCP:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds, None)
+    else:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("grpc.secure_channel")
+def test_create_channel_explicit_with_quota_project(
+    grpc_secure_channel, composite_creds_call
+):
+    target = "example.com:443"
+    composite_creds = composite_creds_call.return_value
+
+    credentials = mock.create_autospec(
+        google.auth.credentials.CredentialsWithQuotaProject, instance=True
+    )
+
+    channel = grpc_helpers.create_channel(
+        target, credentials=credentials, quota_project_id="project-foo"
+    )
+
+    credentials.with_quota_project.assert_called_once_with("project-foo")
+
+    assert channel is grpc_secure_channel.return_value
+    if grpc_helpers.HAS_GRPC_GCP:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds, None)
+    else:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("grpc.secure_channel")
+@mock.patch(
+    "google.auth.load_credentials_from_file",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.project),
+)
+def test_create_channel_with_credentials_file(
+    load_credentials_from_file, grpc_secure_channel, composite_creds_call
+):
+    target = "example.com:443"
+
+    credentials_file = "/path/to/credentials/file.json"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers.create_channel(target, credentials_file=credentials_file)
+
+    google.auth.load_credentials_from_file.assert_called_once_with(
+        credentials_file, scopes=None, default_scopes=None
+    )
+
+    assert channel is grpc_secure_channel.return_value
+    if grpc_helpers.HAS_GRPC_GCP:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds, None)
+    else:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("grpc.secure_channel")
+@mock.patch(
+    "google.auth.load_credentials_from_file",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.project),
+)
+def test_create_channel_with_credentials_file_and_scopes(
+    load_credentials_from_file, grpc_secure_channel, composite_creds_call
+):
+    target = "example.com:443"
+    scopes = ["1", "2"]
+
+    credentials_file = "/path/to/credentials/file.json"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers.create_channel(
+        target, credentials_file=credentials_file, scopes=scopes
+    )
+
+    google.auth.load_credentials_from_file.assert_called_once_with(
+        credentials_file, scopes=scopes, default_scopes=None
+    )
+
+    assert channel is grpc_secure_channel.return_value
+    if grpc_helpers.HAS_GRPC_GCP:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds, None)
+    else:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@mock.patch("grpc.composite_channel_credentials")
+@mock.patch("grpc.secure_channel")
+@mock.patch(
+    "google.auth.load_credentials_from_file",
+    autospec=True,
+    return_value=(mock.sentinel.credentials, mock.sentinel.project),
+)
+def test_create_channel_with_credentials_file_and_default_scopes(
+    load_credentials_from_file, grpc_secure_channel, composite_creds_call
+):
+    target = "example.com:443"
+    default_scopes = ["3", "4"]
+
+    credentials_file = "/path/to/credentials/file.json"
+    composite_creds = composite_creds_call.return_value
+
+    channel = grpc_helpers.create_channel(
+        target, credentials_file=credentials_file, default_scopes=default_scopes
+    )
+
+    load_credentials_from_file.assert_called_once_with(
+        credentials_file, scopes=None, default_scopes=default_scopes
+    )
+
+    assert channel is grpc_secure_channel.return_value
+    if grpc_helpers.HAS_GRPC_GCP:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds, None)
+    else:
+        grpc_secure_channel.assert_called_once_with(target, composite_creds)
+
+
+@pytest.mark.skipif(
+    not grpc_helpers.HAS_GRPC_GCP, reason="grpc_gcp module not available"
+)
+@mock.patch("grpc_gcp.secure_channel")
+def test_create_channel_with_grpc_gcp(grpc_gcp_secure_channel):
+    target = "example.com:443"
+    scopes = ["test_scope"]
+
+    credentials = mock.create_autospec(google.auth.credentials.Scoped, instance=True)
+    credentials.requires_scopes = True
+
+    grpc_helpers.create_channel(target, credentials=credentials, scopes=scopes)
+    grpc_gcp_secure_channel.assert_called()
+
+    credentials.with_scopes.assert_called_once_with(scopes, default_scopes=None)
+
+
+@pytest.mark.skipif(grpc_helpers.HAS_GRPC_GCP, reason="grpc_gcp module not available")
+@mock.patch("grpc.secure_channel")
+def test_create_channel_without_grpc_gcp(grpc_secure_channel):
+    target = "example.com:443"
+    scopes = ["test_scope"]
+
+    credentials = mock.create_autospec(google.auth.credentials.Scoped, instance=True)
+    credentials.requires_scopes = True
+
+    grpc_helpers.create_channel(target, credentials=credentials, scopes=scopes)
+    grpc_secure_channel.assert_called()
+
+    credentials.with_scopes.assert_called_once_with(scopes, default_scopes=None)
+
+
+class TestChannelStub(object):
+    def test_single_response(self):
+        channel = grpc_helpers.ChannelStub()
+        stub = operations_pb2.OperationsStub(channel)
+        expected_request = operations_pb2.GetOperationRequest(name="meep")
+        expected_response = operations_pb2.Operation(name="moop")
+
+        channel.GetOperation.response = expected_response
+
+        response = stub.GetOperation(expected_request)
+
+        assert response == expected_response
+        assert channel.requests == [("GetOperation", expected_request)]
+        assert channel.GetOperation.requests == [expected_request]
+
+    def test_no_response(self):
+        channel = grpc_helpers.ChannelStub()
+        stub = operations_pb2.OperationsStub(channel)
+        expected_request = operations_pb2.GetOperationRequest(name="meep")
+
+        with pytest.raises(ValueError) as exc_info:
+            stub.GetOperation(expected_request)
+
+        assert exc_info.match("GetOperation")
+
+    def test_missing_method(self):
+        channel = grpc_helpers.ChannelStub()
+
+        with pytest.raises(AttributeError):
+            channel.DoesNotExist.response
+
+    def test_exception_response(self):
+        channel = grpc_helpers.ChannelStub()
+        stub = operations_pb2.OperationsStub(channel)
+        expected_request = operations_pb2.GetOperationRequest(name="meep")
+
+        channel.GetOperation.response = RuntimeError()
+
+        with pytest.raises(RuntimeError):
+            stub.GetOperation(expected_request)
+
+    def test_callable_response(self):
+        channel = grpc_helpers.ChannelStub()
+        stub = operations_pb2.OperationsStub(channel)
+        expected_request = operations_pb2.GetOperationRequest(name="meep")
+        expected_response = operations_pb2.Operation(name="moop")
+
+        on_get_operation = mock.Mock(spec=("__call__",), return_value=expected_response)
+
+        channel.GetOperation.response = on_get_operation
+
+        response = stub.GetOperation(expected_request)
+
+        assert response == expected_response
+        on_get_operation.assert_called_once_with(expected_request)
+
+    def test_multiple_responses(self):
+        channel = grpc_helpers.ChannelStub()
+        stub = operations_pb2.OperationsStub(channel)
+        expected_request = operations_pb2.GetOperationRequest(name="meep")
+        expected_responses = [
+            operations_pb2.Operation(name="foo"),
+            operations_pb2.Operation(name="bar"),
+            operations_pb2.Operation(name="baz"),
+        ]
+
+        channel.GetOperation.responses = iter(expected_responses)
+
+        response1 = stub.GetOperation(expected_request)
+        response2 = stub.GetOperation(expected_request)
+        response3 = stub.GetOperation(expected_request)
+
+        assert response1 == expected_responses[0]
+        assert response2 == expected_responses[1]
+        assert response3 == expected_responses[2]
+        assert channel.requests == [("GetOperation", expected_request)] * 3
+        assert channel.GetOperation.requests == [expected_request] * 3
+
+        with pytest.raises(StopIteration):
+            stub.GetOperation(expected_request)
+
+    def test_multiple_responses_and_single_response_error(self):
+        channel = grpc_helpers.ChannelStub()
+        stub = operations_pb2.OperationsStub(channel)
+        channel.GetOperation.responses = []
+        channel.GetOperation.response = mock.sentinel.response
+
+        with pytest.raises(ValueError):
+            stub.GetOperation(operations_pb2.GetOperationRequest())
+
+    def test_call_info(self):
+        channel = grpc_helpers.ChannelStub()
+        stub = operations_pb2.OperationsStub(channel)
+        expected_request = operations_pb2.GetOperationRequest(name="meep")
+        expected_response = operations_pb2.Operation(name="moop")
+        expected_metadata = [("red", "blue"), ("two", "shoe")]
+        expected_credentials = mock.sentinel.credentials
+        channel.GetOperation.response = expected_response
+
+        response = stub.GetOperation(
+            expected_request,
+            timeout=42,
+            metadata=expected_metadata,
+            credentials=expected_credentials,
+        )
+
+        assert response == expected_response
+        assert channel.requests == [("GetOperation", expected_request)]
+        assert channel.GetOperation.calls == [
+            (expected_request, 42, expected_metadata, expected_credentials)
+        ]
+
+    def test_unary_unary(self):
+        channel = grpc_helpers.ChannelStub()
+        method_name = "GetOperation"
+        callable_stub = channel.unary_unary(method_name)
+        assert callable_stub._method == method_name
+        assert callable_stub._channel == channel
+
+    def test_unary_stream(self):
+        channel = grpc_helpers.ChannelStub()
+        method_name = "GetOperation"
+        callable_stub = channel.unary_stream(method_name)
+        assert callable_stub._method == method_name
+        assert callable_stub._channel == channel
+
+    def test_stream_unary(self):
+        channel = grpc_helpers.ChannelStub()
+        method_name = "GetOperation"
+        callable_stub = channel.stream_unary(method_name)
+        assert callable_stub._method == method_name
+        assert callable_stub._channel == channel
+
+    def test_stream_stream(self):
+        channel = grpc_helpers.ChannelStub()
+        method_name = "GetOperation"
+        callable_stub = channel.stream_stream(method_name)
+        assert callable_stub._method == method_name
+        assert callable_stub._channel == channel
+
+    def test_subscribe_unsubscribe(self):
+        channel = grpc_helpers.ChannelStub()
+        assert channel.subscribe(None) is None
+        assert channel.unsubscribe(None) is None
+
+    def test_close(self):
+        channel = grpc_helpers.ChannelStub()
+        assert channel.close() is None
diff --git a/tests/unit/test_iam.py b/tests/unit/test_iam.py
new file mode 100644
index 0000000..fbd242e
--- /dev/null
+++ b/tests/unit/test_iam.py
@@ -0,0 +1,382 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import pytest
+
+from google.api_core.iam import _DICT_ACCESS_MSG, InvalidOperationException
+
+
+class TestPolicy:
+    @staticmethod
+    def _get_target_class():
+        from google.api_core.iam import Policy
+
+        return Policy
+
+    def _make_one(self, *args, **kw):
+        return self._get_target_class()(*args, **kw)
+
+    def test_ctor_defaults(self):
+        empty = frozenset()
+        policy = self._make_one()
+        assert policy.etag is None
+        assert policy.version is None
+        assert policy.owners == empty
+        assert policy.editors == empty
+        assert policy.viewers == empty
+        assert len(policy) == 0
+        assert dict(policy) == {}
+
+    def test_ctor_explicit(self):
+        VERSION = 1
+        ETAG = "ETAG"
+        empty = frozenset()
+        policy = self._make_one(ETAG, VERSION)
+        assert policy.etag == ETAG
+        assert policy.version == VERSION
+        assert policy.owners == empty
+        assert policy.editors == empty
+        assert policy.viewers == empty
+        assert len(policy) == 0
+        assert dict(policy) == {}
+
+    def test___getitem___miss(self):
+        policy = self._make_one()
+        assert policy["nonesuch"] == set()
+
+    def test__getitem___and_set(self):
+        from google.api_core.iam import OWNER_ROLE
+
+        policy = self._make_one()
+
+        # get the policy using the getter and then modify it
+        policy[OWNER_ROLE].add("user:phred@example.com")
+        assert dict(policy) == {OWNER_ROLE: {"user:phred@example.com"}}
+
+    def test___getitem___version3(self):
+        policy = self._make_one("DEADBEEF", 3)
+        with pytest.raises(InvalidOperationException, match=_DICT_ACCESS_MSG):
+            policy["role"]
+
+    def test___getitem___with_conditions(self):
+        USER = "user:phred@example.com"
+        CONDITION = {"expression": "2 > 1"}
+        policy = self._make_one("DEADBEEF", 1)
+        policy.bindings = [
+            {"role": "role/reader", "members": [USER], "condition": CONDITION}
+        ]
+        with pytest.raises(InvalidOperationException, match=_DICT_ACCESS_MSG):
+            policy["role/reader"]
+
+    def test___setitem__(self):
+        USER = "user:phred@example.com"
+        PRINCIPALS = set([USER])
+        policy = self._make_one()
+        policy["rolename"] = [USER]
+        assert policy["rolename"] == PRINCIPALS
+        assert len(policy) == 1
+        assert dict(policy) == {"rolename": PRINCIPALS}
+
+    def test__set_item__overwrite(self):
+        GROUP = "group:test@group.com"
+        USER = "user:phred@example.com"
+        ALL_USERS = "allUsers"
+        MEMBERS = set([ALL_USERS])
+        GROUPS = set([GROUP])
+        policy = self._make_one()
+        policy["first"] = [GROUP]
+        policy["second"] = [USER]
+        policy["second"] = [ALL_USERS]
+        assert policy["second"] == MEMBERS
+        assert len(policy) == 2
+        assert dict(policy) == {"first": GROUPS, "second": MEMBERS}
+
+    def test___setitem___version3(self):
+        policy = self._make_one("DEADBEEF", 3)
+        with pytest.raises(InvalidOperationException, match=_DICT_ACCESS_MSG):
+            policy["role/reader"] = ["user:phred@example.com"]
+
+    def test___setitem___with_conditions(self):
+        USER = "user:phred@example.com"
+        CONDITION = {"expression": "2 > 1"}
+        policy = self._make_one("DEADBEEF", 1)
+        policy.bindings = [
+            {"role": "role/reader", "members": set([USER]), "condition": CONDITION}
+        ]
+        with pytest.raises(InvalidOperationException, match=_DICT_ACCESS_MSG):
+            policy["role/reader"] = ["user:phred@example.com"]
+
+    def test___delitem___hit(self):
+        policy = self._make_one()
+        policy.bindings = [
+            {"role": "to/keep", "members": set(["phred@example.com"])},
+            {"role": "to/remove", "members": set(["phred@example.com"])},
+        ]
+        del policy["to/remove"]
+        assert len(policy) == 1
+        assert dict(policy) == {"to/keep": set(["phred@example.com"])}
+
+    def test___delitem___miss(self):
+        policy = self._make_one()
+        with pytest.raises(KeyError):
+            del policy["nonesuch"]
+
+    def test___delitem___version3(self):
+        policy = self._make_one("DEADBEEF", 3)
+        with pytest.raises(InvalidOperationException, match=_DICT_ACCESS_MSG):
+            del policy["role/reader"]
+
+    def test___delitem___with_conditions(self):
+        USER = "user:phred@example.com"
+        CONDITION = {"expression": "2 > 1"}
+        policy = self._make_one("DEADBEEF", 1)
+        policy.bindings = [
+            {"role": "role/reader", "members": set([USER]), "condition": CONDITION}
+        ]
+        with pytest.raises(InvalidOperationException, match=_DICT_ACCESS_MSG):
+            del policy["role/reader"]
+
+    def test_bindings_property(self):
+        USER = "user:phred@example.com"
+        CONDITION = {"expression": "2 > 1"}
+        policy = self._make_one()
+        BINDINGS = [
+            {"role": "role/reader", "members": set([USER]), "condition": CONDITION}
+        ]
+        policy.bindings = BINDINGS
+        assert policy.bindings == BINDINGS
+
+    def test_owners_getter(self):
+        from google.api_core.iam import OWNER_ROLE
+
+        MEMBER = "user:phred@example.com"
+        expected = frozenset([MEMBER])
+        policy = self._make_one()
+        policy[OWNER_ROLE] = [MEMBER]
+        assert policy.owners == expected
+
+    def test_owners_setter(self):
+        import warnings
+        from google.api_core.iam import OWNER_ROLE
+
+        MEMBER = "user:phred@example.com"
+        expected = set([MEMBER])
+        policy = self._make_one()
+
+        with warnings.catch_warnings(record=True) as warned:
+            policy.owners = [MEMBER]
+
+        (warning,) = warned
+        assert warning.category is DeprecationWarning
+        assert policy[OWNER_ROLE] == expected
+
+    def test_editors_getter(self):
+        from google.api_core.iam import EDITOR_ROLE
+
+        MEMBER = "user:phred@example.com"
+        expected = frozenset([MEMBER])
+        policy = self._make_one()
+        policy[EDITOR_ROLE] = [MEMBER]
+        assert policy.editors == expected
+
+    def test_editors_setter(self):
+        import warnings
+        from google.api_core.iam import EDITOR_ROLE
+
+        MEMBER = "user:phred@example.com"
+        expected = set([MEMBER])
+        policy = self._make_one()
+
+        with warnings.catch_warnings(record=True) as warned:
+            policy.editors = [MEMBER]
+
+        (warning,) = warned
+        assert warning.category is DeprecationWarning
+        assert policy[EDITOR_ROLE] == expected
+
+    def test_viewers_getter(self):
+        from google.api_core.iam import VIEWER_ROLE
+
+        MEMBER = "user:phred@example.com"
+        expected = frozenset([MEMBER])
+        policy = self._make_one()
+        policy[VIEWER_ROLE] = [MEMBER]
+        assert policy.viewers == expected
+
+    def test_viewers_setter(self):
+        import warnings
+        from google.api_core.iam import VIEWER_ROLE
+
+        MEMBER = "user:phred@example.com"
+        expected = set([MEMBER])
+        policy = self._make_one()
+
+        with warnings.catch_warnings(record=True) as warned:
+            policy.viewers = [MEMBER]
+
+        (warning,) = warned
+        assert warning.category is DeprecationWarning
+        assert policy[VIEWER_ROLE] == expected
+
+    def test_user(self):
+        EMAIL = "phred@example.com"
+        MEMBER = "user:%s" % (EMAIL,)
+        policy = self._make_one()
+        assert policy.user(EMAIL) == MEMBER
+
+    def test_service_account(self):
+        EMAIL = "phred@example.com"
+        MEMBER = "serviceAccount:%s" % (EMAIL,)
+        policy = self._make_one()
+        assert policy.service_account(EMAIL) == MEMBER
+
+    def test_group(self):
+        EMAIL = "phred@example.com"
+        MEMBER = "group:%s" % (EMAIL,)
+        policy = self._make_one()
+        assert policy.group(EMAIL) == MEMBER
+
+    def test_domain(self):
+        DOMAIN = "example.com"
+        MEMBER = "domain:%s" % (DOMAIN,)
+        policy = self._make_one()
+        assert policy.domain(DOMAIN) == MEMBER
+
+    def test_all_users(self):
+        policy = self._make_one()
+        assert policy.all_users() == "allUsers"
+
+    def test_authenticated_users(self):
+        policy = self._make_one()
+        assert policy.authenticated_users() == "allAuthenticatedUsers"
+
+    def test_from_api_repr_only_etag(self):
+        empty = frozenset()
+        RESOURCE = {"etag": "ACAB"}
+        klass = self._get_target_class()
+        policy = klass.from_api_repr(RESOURCE)
+        assert policy.etag == "ACAB"
+        assert policy.version is None
+        assert policy.owners == empty
+        assert policy.editors == empty
+        assert policy.viewers == empty
+        assert dict(policy) == {}
+
+    def test_from_api_repr_complete(self):
+        from google.api_core.iam import OWNER_ROLE, EDITOR_ROLE, VIEWER_ROLE
+
+        OWNER1 = "group:cloud-logs@google.com"
+        OWNER2 = "user:phred@example.com"
+        EDITOR1 = "domain:google.com"
+        EDITOR2 = "user:phred@example.com"
+        VIEWER1 = "serviceAccount:1234-abcdef@service.example.com"
+        VIEWER2 = "user:phred@example.com"
+        RESOURCE = {
+            "etag": "DEADBEEF",
+            "version": 1,
+            "bindings": [
+                {"role": OWNER_ROLE, "members": [OWNER1, OWNER2]},
+                {"role": EDITOR_ROLE, "members": [EDITOR1, EDITOR2]},
+                {"role": VIEWER_ROLE, "members": [VIEWER1, VIEWER2]},
+            ],
+        }
+        klass = self._get_target_class()
+        policy = klass.from_api_repr(RESOURCE)
+        assert policy.etag == "DEADBEEF"
+        assert policy.version == 1
+        assert policy.owners, frozenset([OWNER1 == OWNER2])
+        assert policy.editors, frozenset([EDITOR1 == EDITOR2])
+        assert policy.viewers, frozenset([VIEWER1 == VIEWER2])
+        assert dict(policy) == {
+            OWNER_ROLE: set([OWNER1, OWNER2]),
+            EDITOR_ROLE: set([EDITOR1, EDITOR2]),
+            VIEWER_ROLE: set([VIEWER1, VIEWER2]),
+        }
+        assert policy.bindings == [
+            {"role": OWNER_ROLE, "members": set([OWNER1, OWNER2])},
+            {"role": EDITOR_ROLE, "members": set([EDITOR1, EDITOR2])},
+            {"role": VIEWER_ROLE, "members": set([VIEWER1, VIEWER2])},
+        ]
+
+    def test_from_api_repr_unknown_role(self):
+        USER = "user:phred@example.com"
+        GROUP = "group:cloud-logs@google.com"
+        RESOURCE = {
+            "etag": "DEADBEEF",
+            "version": 1,
+            "bindings": [{"role": "unknown", "members": [USER, GROUP]}],
+        }
+        klass = self._get_target_class()
+        policy = klass.from_api_repr(RESOURCE)
+        assert policy.etag == "DEADBEEF"
+        assert policy.version == 1
+        assert dict(policy), {"unknown": set([GROUP == USER])}
+
+    def test_to_api_repr_defaults(self):
+        policy = self._make_one()
+        assert policy.to_api_repr() == {}
+
+    def test_to_api_repr_only_etag(self):
+        policy = self._make_one("DEADBEEF")
+        assert policy.to_api_repr() == {"etag": "DEADBEEF"}
+
+    def test_to_api_repr_binding_wo_members(self):
+        policy = self._make_one()
+        policy["empty"] = []
+        assert policy.to_api_repr() == {}
+
+    def test_to_api_repr_binding_w_duplicates(self):
+        import warnings
+        from google.api_core.iam import OWNER_ROLE
+
+        OWNER = "group:cloud-logs@google.com"
+        policy = self._make_one()
+        with warnings.catch_warnings(record=True):
+            policy.owners = [OWNER, OWNER]
+        assert policy.to_api_repr() == {
+            "bindings": [{"role": OWNER_ROLE, "members": [OWNER]}]
+        }
+
+    def test_to_api_repr_full(self):
+        import operator
+        from google.api_core.iam import OWNER_ROLE, EDITOR_ROLE, VIEWER_ROLE
+
+        OWNER1 = "group:cloud-logs@google.com"
+        OWNER2 = "user:phred@example.com"
+        EDITOR1 = "domain:google.com"
+        EDITOR2 = "user:phred@example.com"
+        VIEWER1 = "serviceAccount:1234-abcdef@service.example.com"
+        VIEWER2 = "user:phred@example.com"
+        CONDITION = {
+            "title": "title",
+            "description": "description",
+            "expression": "true",
+        }
+        BINDINGS = [
+            {"role": OWNER_ROLE, "members": [OWNER1, OWNER2]},
+            {"role": EDITOR_ROLE, "members": [EDITOR1, EDITOR2]},
+            {"role": VIEWER_ROLE, "members": [VIEWER1, VIEWER2]},
+            {
+                "role": VIEWER_ROLE,
+                "members": [VIEWER1, VIEWER2],
+                "condition": CONDITION,
+            },
+        ]
+        policy = self._make_one("DEADBEEF", 1)
+        policy.bindings = BINDINGS
+        resource = policy.to_api_repr()
+        assert resource["etag"] == "DEADBEEF"
+        assert resource["version"] == 1
+        key = operator.itemgetter("role")
+        assert sorted(resource["bindings"], key=key) == sorted(BINDINGS, key=key)
diff --git a/tests/unit/test_operation.py b/tests/unit/test_operation.py
new file mode 100644
index 0000000..22e23bc
--- /dev/null
+++ b/tests/unit/test_operation.py
@@ -0,0 +1,326 @@
+# Copyright 2017, Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+import mock
+import pytest
+
+try:
+    import grpc  # noqa: F401
+except ImportError:
+    pytest.skip("No GRPC", allow_module_level=True)
+
+from google.api_core import exceptions
+from google.api_core import operation
+from google.api_core import operations_v1
+from google.api_core import retry
+from google.longrunning import operations_pb2
+from google.protobuf import struct_pb2
+from google.rpc import code_pb2
+from google.rpc import status_pb2
+
+TEST_OPERATION_NAME = "test/operation"
+
+
+def make_operation_proto(
+    name=TEST_OPERATION_NAME, metadata=None, response=None, error=None, **kwargs
+):
+    operation_proto = operations_pb2.Operation(name=name, **kwargs)
+
+    if metadata is not None:
+        operation_proto.metadata.Pack(metadata)
+
+    if response is not None:
+        operation_proto.response.Pack(response)
+
+    if error is not None:
+        operation_proto.error.CopyFrom(error)
+
+    return operation_proto
+
+
+def make_operation_future(client_operations_responses=None):
+    if client_operations_responses is None:
+        client_operations_responses = [make_operation_proto()]
+
+    refresh = mock.Mock(spec=["__call__"], side_effect=client_operations_responses)
+    refresh.responses = client_operations_responses
+    cancel = mock.Mock(spec=["__call__"])
+    operation_future = operation.Operation(
+        client_operations_responses[0],
+        refresh,
+        cancel,
+        result_type=struct_pb2.Struct,
+        metadata_type=struct_pb2.Struct,
+    )
+
+    return operation_future, refresh, cancel
+
+
+def test_constructor():
+    future, refresh, _ = make_operation_future()
+
+    assert future.operation == refresh.responses[0]
+    assert future.operation.done is False
+    assert future.operation.name == TEST_OPERATION_NAME
+    assert future.metadata is None
+    assert future.running()
+
+
+def test_metadata():
+    expected_metadata = struct_pb2.Struct()
+    future, _, _ = make_operation_future(
+        [make_operation_proto(metadata=expected_metadata)]
+    )
+
+    assert future.metadata == expected_metadata
+
+
+def test_cancellation():
+    responses = [
+        make_operation_proto(),
+        # Second response indicates that the operation was cancelled.
+        make_operation_proto(
+            done=True, error=status_pb2.Status(code=code_pb2.CANCELLED)
+        ),
+    ]
+    future, _, cancel = make_operation_future(responses)
+
+    assert future.cancel()
+    assert future.cancelled()
+    cancel.assert_called_once_with()
+
+    # Cancelling twice should have no effect.
+    assert not future.cancel()
+    cancel.assert_called_once_with()
+
+
+def test_result():
+    expected_result = struct_pb2.Struct()
+    responses = [
+        make_operation_proto(),
+        # Second operation response includes the result.
+        make_operation_proto(done=True, response=expected_result),
+    ]
+    future, _, _ = make_operation_future(responses)
+
+    result = future.result()
+
+    assert result == expected_result
+    assert future.done()
+
+
+def test_done_w_retry():
+    RETRY_PREDICATE = retry.if_exception_type(exceptions.TooManyRequests)
+    test_retry = retry.Retry(predicate=RETRY_PREDICATE)
+
+    expected_result = struct_pb2.Struct()
+    responses = [
+        make_operation_proto(),
+        # Second operation response includes the result.
+        make_operation_proto(done=True, response=expected_result),
+    ]
+    future, _, _ = make_operation_future(responses)
+    future._refresh = mock.Mock()
+
+    future.done(retry=test_retry)
+    future._refresh.assert_called_once_with(retry=test_retry)
+
+
+def test_exception():
+    expected_exception = status_pb2.Status(message="meep")
+    responses = [
+        make_operation_proto(),
+        # Second operation response includes the error.
+        make_operation_proto(done=True, error=expected_exception),
+    ]
+    future, _, _ = make_operation_future(responses)
+
+    exception = future.exception()
+
+    assert expected_exception.message in "{!r}".format(exception)
+
+
+def test_exception_with_error_code():
+    expected_exception = status_pb2.Status(message="meep", code=5)
+    responses = [
+        make_operation_proto(),
+        # Second operation response includes the error.
+        make_operation_proto(done=True, error=expected_exception),
+    ]
+    future, _, _ = make_operation_future(responses)
+
+    exception = future.exception()
+
+    assert expected_exception.message in "{!r}".format(exception)
+    # Status Code 5 maps to Not Found
+    # https://developers.google.com/maps-booking/reference/grpc-api/status_codes
+    assert isinstance(exception, exceptions.NotFound)
+
+
+def test_unexpected_result():
+    responses = [
+        make_operation_proto(),
+        # Second operation response is done, but has not error or response.
+        make_operation_proto(done=True),
+    ]
+    future, _, _ = make_operation_future(responses)
+
+    exception = future.exception()
+
+    assert "Unexpected state" in "{!r}".format(exception)
+
+
+def test__refresh_http():
+    json_response = {"name": TEST_OPERATION_NAME, "done": True}
+    api_request = mock.Mock(return_value=json_response)
+
+    result = operation._refresh_http(api_request, TEST_OPERATION_NAME)
+
+    assert isinstance(result, operations_pb2.Operation)
+    assert result.name == TEST_OPERATION_NAME
+    assert result.done is True
+
+    api_request.assert_called_once_with(
+        method="GET", path="operations/{}".format(TEST_OPERATION_NAME)
+    )
+
+
+def test__refresh_http_w_retry():
+    json_response = {"name": TEST_OPERATION_NAME, "done": True}
+    api_request = mock.Mock()
+    retry = mock.Mock()
+    retry.return_value.return_value = json_response
+
+    result = operation._refresh_http(api_request, TEST_OPERATION_NAME, retry=retry)
+
+    assert isinstance(result, operations_pb2.Operation)
+    assert result.name == TEST_OPERATION_NAME
+    assert result.done is True
+
+    api_request.assert_not_called()
+    retry.assert_called_once_with(api_request)
+    retry.return_value.assert_called_once_with(
+        method="GET", path="operations/{}".format(TEST_OPERATION_NAME)
+    )
+
+
+def test__cancel_http():
+    api_request = mock.Mock()
+
+    operation._cancel_http(api_request, TEST_OPERATION_NAME)
+
+    api_request.assert_called_once_with(
+        method="POST", path="operations/{}:cancel".format(TEST_OPERATION_NAME)
+    )
+
+
+def test_from_http_json():
+    operation_json = {"name": TEST_OPERATION_NAME, "done": True}
+    api_request = mock.sentinel.api_request
+
+    future = operation.from_http_json(
+        operation_json, api_request, struct_pb2.Struct, metadata_type=struct_pb2.Struct
+    )
+
+    assert future._result_type == struct_pb2.Struct
+    assert future._metadata_type == struct_pb2.Struct
+    assert future.operation.name == TEST_OPERATION_NAME
+    assert future.done
+
+
+def test__refresh_grpc():
+    operations_stub = mock.Mock(spec=["GetOperation"])
+    expected_result = make_operation_proto(done=True)
+    operations_stub.GetOperation.return_value = expected_result
+
+    result = operation._refresh_grpc(operations_stub, TEST_OPERATION_NAME)
+
+    assert result == expected_result
+    expected_request = operations_pb2.GetOperationRequest(name=TEST_OPERATION_NAME)
+    operations_stub.GetOperation.assert_called_once_with(expected_request)
+
+
+def test__refresh_grpc_w_retry():
+    operations_stub = mock.Mock(spec=["GetOperation"])
+    expected_result = make_operation_proto(done=True)
+    retry = mock.Mock()
+    retry.return_value.return_value = expected_result
+
+    result = operation._refresh_grpc(operations_stub, TEST_OPERATION_NAME, retry=retry)
+
+    assert result == expected_result
+    expected_request = operations_pb2.GetOperationRequest(name=TEST_OPERATION_NAME)
+    operations_stub.GetOperation.assert_not_called()
+    retry.assert_called_once_with(operations_stub.GetOperation)
+    retry.return_value.assert_called_once_with(expected_request)
+
+
+def test__cancel_grpc():
+    operations_stub = mock.Mock(spec=["CancelOperation"])
+
+    operation._cancel_grpc(operations_stub, TEST_OPERATION_NAME)
+
+    expected_request = operations_pb2.CancelOperationRequest(name=TEST_OPERATION_NAME)
+    operations_stub.CancelOperation.assert_called_once_with(expected_request)
+
+
+def test_from_grpc():
+    operation_proto = make_operation_proto(done=True)
+    operations_stub = mock.sentinel.operations_stub
+
+    future = operation.from_grpc(
+        operation_proto,
+        operations_stub,
+        struct_pb2.Struct,
+        metadata_type=struct_pb2.Struct,
+        grpc_metadata=[("x-goog-request-params", "foo")],
+    )
+
+    assert future._result_type == struct_pb2.Struct
+    assert future._metadata_type == struct_pb2.Struct
+    assert future.operation.name == TEST_OPERATION_NAME
+    assert future.done
+    assert future._refresh.keywords["metadata"] == [("x-goog-request-params", "foo")]
+    assert future._cancel.keywords["metadata"] == [("x-goog-request-params", "foo")]
+
+
+def test_from_gapic():
+    operation_proto = make_operation_proto(done=True)
+    operations_client = mock.create_autospec(
+        operations_v1.OperationsClient, instance=True
+    )
+
+    future = operation.from_gapic(
+        operation_proto,
+        operations_client,
+        struct_pb2.Struct,
+        metadata_type=struct_pb2.Struct,
+        grpc_metadata=[("x-goog-request-params", "foo")],
+    )
+
+    assert future._result_type == struct_pb2.Struct
+    assert future._metadata_type == struct_pb2.Struct
+    assert future.operation.name == TEST_OPERATION_NAME
+    assert future.done
+    assert future._refresh.keywords["metadata"] == [("x-goog-request-params", "foo")]
+    assert future._cancel.keywords["metadata"] == [("x-goog-request-params", "foo")]
+
+
+def test_deserialize():
+    op = make_operation_proto(name="foobarbaz")
+    serialized = op.SerializeToString()
+    deserialized_op = operation.Operation.deserialize(serialized)
+    assert op.name == deserialized_op.name
+    assert type(op) is type(deserialized_op)
diff --git a/tests/unit/test_page_iterator.py b/tests/unit/test_page_iterator.py
new file mode 100644
index 0000000..a44e998
--- /dev/null
+++ b/tests/unit/test_page_iterator.py
@@ -0,0 +1,665 @@
+# Copyright 2015 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import math
+import types
+
+import mock
+import pytest
+
+from google.api_core import page_iterator
+
+
+def test__do_nothing_page_start():
+    assert page_iterator._do_nothing_page_start(None, None, None) is None
+
+
+class TestPage(object):
+    def test_constructor(self):
+        parent = mock.sentinel.parent
+        item_to_value = mock.sentinel.item_to_value
+
+        page = page_iterator.Page(parent, (1, 2, 3), item_to_value)
+
+        assert page.num_items == 3
+        assert page.remaining == 3
+        assert page._parent is parent
+        assert page._item_to_value is item_to_value
+        assert page.raw_page is None
+
+    def test___iter__(self):
+        page = page_iterator.Page(None, (), None, None)
+        assert iter(page) is page
+
+    def test_iterator_calls_parent_item_to_value(self):
+        parent = mock.sentinel.parent
+
+        item_to_value = mock.Mock(
+            side_effect=lambda iterator, value: value, spec=["__call__"]
+        )
+
+        page = page_iterator.Page(parent, (10, 11, 12), item_to_value)
+        page._remaining = 100
+
+        assert item_to_value.call_count == 0
+        assert page.remaining == 100
+
+        assert next(page) == 10
+        assert item_to_value.call_count == 1
+        item_to_value.assert_called_with(parent, 10)
+        assert page.remaining == 99
+
+        assert next(page) == 11
+        assert item_to_value.call_count == 2
+        item_to_value.assert_called_with(parent, 11)
+        assert page.remaining == 98
+
+        assert next(page) == 12
+        assert item_to_value.call_count == 3
+        item_to_value.assert_called_with(parent, 12)
+        assert page.remaining == 97
+
+    def test_raw_page(self):
+        parent = mock.sentinel.parent
+        item_to_value = mock.sentinel.item_to_value
+
+        raw_page = mock.sentinel.raw_page
+
+        page = page_iterator.Page(parent, (1, 2, 3), item_to_value, raw_page=raw_page)
+        assert page.raw_page is raw_page
+
+        with pytest.raises(AttributeError):
+            page.raw_page = None
+
+
+class PageIteratorImpl(page_iterator.Iterator):
+    def _next_page(self):
+        return mock.create_autospec(page_iterator.Page, instance=True)
+
+
+class TestIterator(object):
+    def test_constructor(self):
+        client = mock.sentinel.client
+        item_to_value = mock.sentinel.item_to_value
+        token = "ab13nceor03"
+        max_results = 1337
+
+        iterator = PageIteratorImpl(
+            client, item_to_value, page_token=token, max_results=max_results
+        )
+
+        assert not iterator._started
+        assert iterator.client is client
+        assert iterator.item_to_value == item_to_value
+        assert iterator.max_results == max_results
+        # Changing attributes.
+        assert iterator.page_number == 0
+        assert iterator.next_page_token == token
+        assert iterator.num_results == 0
+
+    def test_next(self):
+        iterator = PageIteratorImpl(None, None)
+        page_1 = page_iterator.Page(
+            iterator, ("item 1.1", "item 1.2"), page_iterator._item_to_value_identity
+        )
+        page_2 = page_iterator.Page(
+            iterator, ("item 2.1",), page_iterator._item_to_value_identity
+        )
+        iterator._next_page = mock.Mock(side_effect=[page_1, page_2, None])
+
+        result = next(iterator)
+        assert result == "item 1.1"
+        result = next(iterator)
+        assert result == "item 1.2"
+        result = next(iterator)
+        assert result == "item 2.1"
+
+        with pytest.raises(StopIteration):
+            next(iterator)
+
+    def test_pages_property_starts(self):
+        iterator = PageIteratorImpl(None, None)
+
+        assert not iterator._started
+
+        assert isinstance(iterator.pages, types.GeneratorType)
+
+        assert iterator._started
+
+    def test_pages_property_restart(self):
+        iterator = PageIteratorImpl(None, None)
+
+        assert iterator.pages
+
+        # Make sure we cannot restart.
+        with pytest.raises(ValueError):
+            assert iterator.pages
+
+    def test__page_iter_increment(self):
+        iterator = PageIteratorImpl(None, None)
+        page = page_iterator.Page(
+            iterator, ("item",), page_iterator._item_to_value_identity
+        )
+        iterator._next_page = mock.Mock(side_effect=[page, None])
+
+        assert iterator.num_results == 0
+
+        page_iter = iterator._page_iter(increment=True)
+        next(page_iter)
+
+        assert iterator.num_results == 1
+
+    def test__page_iter_no_increment(self):
+        iterator = PageIteratorImpl(None, None)
+
+        assert iterator.num_results == 0
+
+        page_iter = iterator._page_iter(increment=False)
+        next(page_iter)
+
+        # results should still be 0 after fetching a page.
+        assert iterator.num_results == 0
+
+    def test__items_iter(self):
+        # Items to be returned.
+        item1 = 17
+        item2 = 100
+        item3 = 211
+
+        # Make pages from mock responses
+        parent = mock.sentinel.parent
+        page1 = page_iterator.Page(
+            parent, (item1, item2), page_iterator._item_to_value_identity
+        )
+        page2 = page_iterator.Page(
+            parent, (item3,), page_iterator._item_to_value_identity
+        )
+
+        iterator = PageIteratorImpl(None, None)
+        iterator._next_page = mock.Mock(side_effect=[page1, page2, None])
+
+        items_iter = iterator._items_iter()
+
+        assert isinstance(items_iter, types.GeneratorType)
+
+        # Consume items and check the state of the iterator.
+        assert iterator.num_results == 0
+
+        assert next(items_iter) == item1
+        assert iterator.num_results == 1
+
+        assert next(items_iter) == item2
+        assert iterator.num_results == 2
+
+        assert next(items_iter) == item3
+        assert iterator.num_results == 3
+
+        with pytest.raises(StopIteration):
+            next(items_iter)
+
+    def test___iter__(self):
+        iterator = PageIteratorImpl(None, None)
+        iterator._next_page = mock.Mock(side_effect=[(1, 2), (3,), None])
+
+        assert not iterator._started
+
+        result = list(iterator)
+
+        assert result == [1, 2, 3]
+        assert iterator._started
+
+    def test___iter__restart(self):
+        iterator = PageIteratorImpl(None, None)
+
+        iter(iterator)
+
+        # Make sure we cannot restart.
+        with pytest.raises(ValueError):
+            iter(iterator)
+
+    def test___iter___restart_after_page(self):
+        iterator = PageIteratorImpl(None, None)
+
+        assert iterator.pages
+
+        # Make sure we cannot restart after starting the page iterator
+        with pytest.raises(ValueError):
+            iter(iterator)
+
+
+class TestHTTPIterator(object):
+    def test_constructor(self):
+        client = mock.sentinel.client
+        path = "/foo"
+        iterator = page_iterator.HTTPIterator(
+            client, mock.sentinel.api_request, path, mock.sentinel.item_to_value
+        )
+
+        assert not iterator._started
+        assert iterator.client is client
+        assert iterator.path == path
+        assert iterator.item_to_value is mock.sentinel.item_to_value
+        assert iterator._items_key == "items"
+        assert iterator.max_results is None
+        assert iterator.extra_params == {}
+        assert iterator._page_start == page_iterator._do_nothing_page_start
+        # Changing attributes.
+        assert iterator.page_number == 0
+        assert iterator.next_page_token is None
+        assert iterator.num_results == 0
+        assert iterator._page_size is None
+
+    def test_constructor_w_extra_param_collision(self):
+        extra_params = {"pageToken": "val"}
+
+        with pytest.raises(ValueError):
+            page_iterator.HTTPIterator(
+                mock.sentinel.client,
+                mock.sentinel.api_request,
+                mock.sentinel.path,
+                mock.sentinel.item_to_value,
+                extra_params=extra_params,
+            )
+
+    def test_iterate(self):
+        path = "/foo"
+        item1 = {"name": "1"}
+        item2 = {"name": "2"}
+        api_request = mock.Mock(return_value={"items": [item1, item2]})
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            api_request,
+            path=path,
+            item_to_value=page_iterator._item_to_value_identity,
+        )
+
+        assert iterator.num_results == 0
+
+        items_iter = iter(iterator)
+
+        val1 = next(items_iter)
+        assert val1 == item1
+        assert iterator.num_results == 1
+
+        val2 = next(items_iter)
+        assert val2 == item2
+        assert iterator.num_results == 2
+
+        with pytest.raises(StopIteration):
+            next(items_iter)
+
+        api_request.assert_called_once_with(method="GET", path=path, query_params={})
+
+    def test__has_next_page_new(self):
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            mock.sentinel.api_request,
+            mock.sentinel.path,
+            mock.sentinel.item_to_value,
+        )
+
+        # The iterator should *always* indicate that it has a next page
+        # when created so that it can fetch the initial page.
+        assert iterator._has_next_page()
+
+    def test__has_next_page_without_token(self):
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            mock.sentinel.api_request,
+            mock.sentinel.path,
+            mock.sentinel.item_to_value,
+        )
+
+        iterator.page_number = 1
+
+        # The iterator should not indicate that it has a new page if the
+        # initial page has been requested and there's no page token.
+        assert not iterator._has_next_page()
+
+    def test__has_next_page_w_number_w_token(self):
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            mock.sentinel.api_request,
+            mock.sentinel.path,
+            mock.sentinel.item_to_value,
+        )
+
+        iterator.page_number = 1
+        iterator.next_page_token = mock.sentinel.token
+
+        # The iterator should indicate that it has a new page if the
+        # initial page has been requested and there's is a page token.
+        assert iterator._has_next_page()
+
+    def test__has_next_page_w_max_results_not_done(self):
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            mock.sentinel.api_request,
+            mock.sentinel.path,
+            mock.sentinel.item_to_value,
+            max_results=3,
+            page_token=mock.sentinel.token,
+        )
+
+        iterator.page_number = 1
+
+        # The iterator should indicate that it has a new page if there
+        # is a page token and it has not consumed more than max_results.
+        assert iterator.num_results < iterator.max_results
+        assert iterator._has_next_page()
+
+    def test__has_next_page_w_max_results_done(self):
+
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            mock.sentinel.api_request,
+            mock.sentinel.path,
+            mock.sentinel.item_to_value,
+            max_results=3,
+            page_token=mock.sentinel.token,
+        )
+
+        iterator.page_number = 1
+        iterator.num_results = 3
+
+        # The iterator should not indicate that it has a new page if there
+        # if it has consumed more than max_results.
+        assert iterator.num_results == iterator.max_results
+        assert not iterator._has_next_page()
+
+    def test__get_query_params_no_token(self):
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            mock.sentinel.api_request,
+            mock.sentinel.path,
+            mock.sentinel.item_to_value,
+        )
+
+        assert iterator._get_query_params() == {}
+
+    def test__get_query_params_w_token(self):
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            mock.sentinel.api_request,
+            mock.sentinel.path,
+            mock.sentinel.item_to_value,
+        )
+        iterator.next_page_token = "token"
+
+        assert iterator._get_query_params() == {"pageToken": iterator.next_page_token}
+
+    def test__get_query_params_w_max_results(self):
+        max_results = 3
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            mock.sentinel.api_request,
+            mock.sentinel.path,
+            mock.sentinel.item_to_value,
+            max_results=max_results,
+        )
+
+        iterator.num_results = 1
+        local_max = max_results - iterator.num_results
+
+        assert iterator._get_query_params() == {"maxResults": local_max}
+
+    def test__get_query_params_extra_params(self):
+        extra_params = {"key": "val"}
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            mock.sentinel.api_request,
+            mock.sentinel.path,
+            mock.sentinel.item_to_value,
+            extra_params=extra_params,
+        )
+
+        assert iterator._get_query_params() == extra_params
+
+    def test__get_next_page_response_with_post(self):
+        path = "/foo"
+        page_response = {"items": ["one", "two"]}
+        api_request = mock.Mock(return_value=page_response)
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            api_request,
+            path=path,
+            item_to_value=page_iterator._item_to_value_identity,
+        )
+        iterator._HTTP_METHOD = "POST"
+
+        response = iterator._get_next_page_response()
+
+        assert response == page_response
+
+        api_request.assert_called_once_with(method="POST", path=path, data={})
+
+    def test__get_next_page_bad_http_method(self):
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            mock.sentinel.api_request,
+            mock.sentinel.path,
+            mock.sentinel.item_to_value,
+        )
+        iterator._HTTP_METHOD = "NOT-A-VERB"
+
+        with pytest.raises(ValueError):
+            iterator._get_next_page_response()
+
+    @pytest.mark.parametrize(
+        "page_size,max_results,pages",
+        [(3, None, False), (3, 8, False), (3, None, True), (3, 8, True)],
+    )
+    def test_page_size_items(self, page_size, max_results, pages):
+        path = "/foo"
+        NITEMS = 10
+
+        n = [0]  # blast you python 2!
+
+        def api_request(*args, **kw):
+            assert not args
+            query_params = dict(
+                maxResults=(
+                    page_size
+                    if max_results is None
+                    else min(page_size, max_results - n[0])
+                )
+            )
+            if n[0]:
+                query_params.update(pageToken="test")
+            assert kw == {"method": "GET", "path": "/foo", "query_params": query_params}
+            n_items = min(kw["query_params"]["maxResults"], NITEMS - n[0])
+            items = [dict(name=str(i + n[0])) for i in range(n_items)]
+            n[0] += n_items
+            result = dict(items=items)
+            if n[0] < NITEMS:
+                result.update(nextPageToken="test")
+            return result
+
+        iterator = page_iterator.HTTPIterator(
+            mock.sentinel.client,
+            api_request,
+            path=path,
+            item_to_value=page_iterator._item_to_value_identity,
+            page_size=page_size,
+            max_results=max_results,
+        )
+
+        assert iterator.num_results == 0
+
+        n_results = max_results if max_results is not None else NITEMS
+        if pages:
+            items_iter = iter(iterator.pages)
+            npages = int(math.ceil(float(n_results) / page_size))
+            for ipage in range(npages):
+                assert list(next(items_iter)) == [
+                    dict(name=str(i))
+                    for i in range(
+                        ipage * page_size, min((ipage + 1) * page_size, n_results),
+                    )
+                ]
+        else:
+            items_iter = iter(iterator)
+            for i in range(n_results):
+                assert next(items_iter) == dict(name=str(i))
+                assert iterator.num_results == i + 1
+
+        with pytest.raises(StopIteration):
+            next(items_iter)
+
+
+class TestGRPCIterator(object):
+    def test_constructor(self):
+        client = mock.sentinel.client
+        items_field = "items"
+        iterator = page_iterator.GRPCIterator(
+            client, mock.sentinel.method, mock.sentinel.request, items_field
+        )
+
+        assert not iterator._started
+        assert iterator.client is client
+        assert iterator.max_results is None
+        assert iterator.item_to_value is page_iterator._item_to_value_identity
+        assert iterator._method == mock.sentinel.method
+        assert iterator._request == mock.sentinel.request
+        assert iterator._items_field == items_field
+        assert (
+            iterator._request_token_field
+            == page_iterator.GRPCIterator._DEFAULT_REQUEST_TOKEN_FIELD
+        )
+        assert (
+            iterator._response_token_field
+            == page_iterator.GRPCIterator._DEFAULT_RESPONSE_TOKEN_FIELD
+        )
+        # Changing attributes.
+        assert iterator.page_number == 0
+        assert iterator.next_page_token is None
+        assert iterator.num_results == 0
+
+    def test_constructor_options(self):
+        client = mock.sentinel.client
+        items_field = "items"
+        request_field = "request"
+        response_field = "response"
+        iterator = page_iterator.GRPCIterator(
+            client,
+            mock.sentinel.method,
+            mock.sentinel.request,
+            items_field,
+            item_to_value=mock.sentinel.item_to_value,
+            request_token_field=request_field,
+            response_token_field=response_field,
+            max_results=42,
+        )
+
+        assert iterator.client is client
+        assert iterator.max_results == 42
+        assert iterator.item_to_value is mock.sentinel.item_to_value
+        assert iterator._method == mock.sentinel.method
+        assert iterator._request == mock.sentinel.request
+        assert iterator._items_field == items_field
+        assert iterator._request_token_field == request_field
+        assert iterator._response_token_field == response_field
+
+    def test_iterate(self):
+        request = mock.Mock(spec=["page_token"], page_token=None)
+        response1 = mock.Mock(items=["a", "b"], next_page_token="1")
+        response2 = mock.Mock(items=["c"], next_page_token="2")
+        response3 = mock.Mock(items=["d"], next_page_token="")
+        method = mock.Mock(side_effect=[response1, response2, response3])
+        iterator = page_iterator.GRPCIterator(
+            mock.sentinel.client, method, request, "items"
+        )
+
+        assert iterator.num_results == 0
+
+        items = list(iterator)
+        assert items == ["a", "b", "c", "d"]
+
+        method.assert_called_with(request)
+        assert method.call_count == 3
+        assert request.page_token == "2"
+
+    def test_iterate_with_max_results(self):
+        request = mock.Mock(spec=["page_token"], page_token=None)
+        response1 = mock.Mock(items=["a", "b"], next_page_token="1")
+        response2 = mock.Mock(items=["c"], next_page_token="2")
+        response3 = mock.Mock(items=["d"], next_page_token="")
+        method = mock.Mock(side_effect=[response1, response2, response3])
+        iterator = page_iterator.GRPCIterator(
+            mock.sentinel.client, method, request, "items", max_results=3
+        )
+
+        assert iterator.num_results == 0
+
+        items = list(iterator)
+
+        assert items == ["a", "b", "c"]
+        assert iterator.num_results == 3
+
+        method.assert_called_with(request)
+        assert method.call_count == 2
+        assert request.page_token == "1"
+
+
+class GAXPageIterator(object):
+    """Fake object that matches gax.PageIterator"""
+
+    def __init__(self, pages, page_token=None):
+        self._pages = iter(pages)
+        self.page_token = page_token
+
+    def next(self):
+        return next(self._pages)
+
+    __next__ = next
+
+
+class TestGAXIterator(object):
+    def test_constructor(self):
+        client = mock.sentinel.client
+        token = "zzzyy78kl"
+        page_iter = GAXPageIterator((), page_token=token)
+        item_to_value = page_iterator._item_to_value_identity
+        max_results = 1337
+        iterator = page_iterator._GAXIterator(
+            client, page_iter, item_to_value, max_results=max_results
+        )
+
+        assert not iterator._started
+        assert iterator.client is client
+        assert iterator.item_to_value is item_to_value
+        assert iterator.max_results == max_results
+        assert iterator._gax_page_iter is page_iter
+        # Changing attributes.
+        assert iterator.page_number == 0
+        assert iterator.next_page_token == token
+        assert iterator.num_results == 0
+
+    def test__next_page(self):
+        page_items = (29, 31)
+        page_token = "2sde98ds2s0hh"
+        page_iter = GAXPageIterator([page_items], page_token=page_token)
+        iterator = page_iterator._GAXIterator(
+            mock.sentinel.client, page_iter, page_iterator._item_to_value_identity
+        )
+
+        page = iterator._next_page()
+
+        assert iterator.next_page_token == page_token
+        assert isinstance(page, page_iterator.Page)
+        assert list(page) == list(page_items)
+
+        next_page = iterator._next_page()
+
+        assert next_page is None
diff --git a/tests/unit/test_path_template.py b/tests/unit/test_path_template.py
new file mode 100644
index 0000000..2c5216e
--- /dev/null
+++ b/tests/unit/test_path_template.py
@@ -0,0 +1,389 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+from __future__ import unicode_literals
+
+import mock
+import pytest
+
+from google.api_core import path_template
+
+
+@pytest.mark.parametrize(
+    "tmpl, args, kwargs, expected_result",
+    [
+        # Basic positional params
+        ["/v1/*", ["a"], {}, "/v1/a"],
+        ["/v1/**", ["a/b"], {}, "/v1/a/b"],
+        ["/v1/*/*", ["a", "b"], {}, "/v1/a/b"],
+        ["/v1/*/*/**", ["a", "b", "c/d"], {}, "/v1/a/b/c/d"],
+        # Basic named params
+        ["/v1/{name}", [], {"name": "parent"}, "/v1/parent"],
+        ["/v1/{name=**}", [], {"name": "parent/child"}, "/v1/parent/child"],
+        # Named params with a sub-template
+        ["/v1/{name=parent/*}", [], {"name": "parent/child"}, "/v1/parent/child"],
+        [
+            "/v1/{name=parent/**}",
+            [],
+            {"name": "parent/child/object"},
+            "/v1/parent/child/object",
+        ],
+        # Combining positional and named params
+        ["/v1/*/{name}", ["a"], {"name": "parent"}, "/v1/a/parent"],
+        ["/v1/{name}/*", ["a"], {"name": "parent"}, "/v1/parent/a"],
+        [
+            "/v1/{parent}/*/{child}/*",
+            ["a", "b"],
+            {"parent": "thor", "child": "thorson"},
+            "/v1/thor/a/thorson/b",
+        ],
+        ["/v1/{name}/**", ["a/b"], {"name": "parent"}, "/v1/parent/a/b"],
+        # Combining positional and named params with sub-templates.
+        [
+            "/v1/{name=parent/*}/*",
+            ["a"],
+            {"name": "parent/child"},
+            "/v1/parent/child/a",
+        ],
+        [
+            "/v1/*/{name=parent/**}",
+            ["a"],
+            {"name": "parent/child/object"},
+            "/v1/a/parent/child/object",
+        ],
+    ],
+)
+def test_expand_success(tmpl, args, kwargs, expected_result):
+    result = path_template.expand(tmpl, *args, **kwargs)
+    assert result == expected_result
+    assert path_template.validate(tmpl, result)
+
+
+@pytest.mark.parametrize(
+    "tmpl, args, kwargs, exc_match",
+    [
+        # Missing positional arg.
+        ["v1/*", [], {}, "Positional"],
+        # Missing named arg.
+        ["v1/{name}", [], {}, "Named"],
+    ],
+)
+def test_expanded_failure(tmpl, args, kwargs, exc_match):
+    with pytest.raises(ValueError, match=exc_match):
+        path_template.expand(tmpl, *args, **kwargs)
+
+
+@pytest.mark.parametrize(
+    "request_obj, field, expected_result",
+    [
+        [{"field": "stringValue"}, "field", "stringValue"],
+        [{"field": "stringValue"}, "nosuchfield", None],
+        [{"field": "stringValue"}, "field.subfield", None],
+        [{"field": {"subfield": "stringValue"}}, "field", None],
+        [{"field": {"subfield": "stringValue"}}, "field.subfield", "stringValue"],
+        [{"field": {"subfield": [1, 2, 3]}}, "field.subfield", [1, 2, 3]],
+        [{"field": {"subfield": "stringValue"}}, "field", None],
+        [{"field": {"subfield": "stringValue"}}, "field.nosuchfield", None],
+        [
+            {"field": {"subfield": {"subsubfield": "stringValue"}}},
+            "field.subfield.subsubfield",
+            "stringValue",
+        ],
+        ["string", "field", None],
+    ],
+)
+def test_get_field(request_obj, field, expected_result):
+    result = path_template.get_field(request_obj, field)
+    assert result == expected_result
+
+
+@pytest.mark.parametrize(
+    "request_obj, field, expected_result",
+    [
+        [{"field": "stringValue"}, "field", {}],
+        [{"field": "stringValue"}, "nosuchfield", {"field": "stringValue"}],
+        [{"field": "stringValue"}, "field.subfield", {"field": "stringValue"}],
+        [{"field": {"subfield": "stringValue"}}, "field.subfield", {"field": {}}],
+        [
+            {"field": {"subfield": "stringValue", "q": "w"}, "e": "f"},
+            "field.subfield",
+            {"field": {"q": "w"}, "e": "f"},
+        ],
+        [
+            {"field": {"subfield": "stringValue"}},
+            "field.nosuchfield",
+            {"field": {"subfield": "stringValue"}},
+        ],
+        [
+            {"field": {"subfield": {"subsubfield": "stringValue", "q": "w"}}},
+            "field.subfield.subsubfield",
+            {"field": {"subfield": {"q": "w"}}},
+        ],
+        ["string", "field", "string"],
+        ["string", "field.subfield", "string"],
+    ],
+)
+def test_delete_field(request_obj, field, expected_result):
+    path_template.delete_field(request_obj, field)
+    assert request_obj == expected_result
+
+
+@pytest.mark.parametrize(
+    "tmpl, path",
+    [
+        # Single segment template, but multi segment value
+        ["v1/*", "v1/a/b"],
+        ["v1/*/*", "v1/a/b/c"],
+        # Single segement named template, but multi segment value
+        ["v1/{name}", "v1/a/b"],
+        ["v1/{name}/{value}", "v1/a/b/c"],
+        # Named value with a sub-template but invalid value
+        ["v1/{name=parent/*}", "v1/grandparent/child"],
+    ],
+)
+def test_validate_failure(tmpl, path):
+    assert not path_template.validate(tmpl, path)
+
+
+def test__expand_variable_match_unexpected():
+    match = mock.Mock(spec=["group"])
+    match.group.return_value = None
+    with pytest.raises(ValueError, match="Unknown"):
+        path_template._expand_variable_match([], {}, match)
+
+
+def test__replace_variable_with_pattern():
+    match = mock.Mock(spec=["group"])
+    match.group.return_value = None
+    with pytest.raises(ValueError, match="Unknown"):
+        path_template._replace_variable_with_pattern(match)
+
+
+@pytest.mark.parametrize(
+    "http_options, request_kwargs, expected_result",
+    [
+        [
+            [["get", "/v1/no/template", ""]],
+            {"foo": "bar"},
+            ["get", "/v1/no/template", {}, {"foo": "bar"}],
+        ],
+        # Single templates
+        [
+            [["get", "/v1/{field}", ""]],
+            {"field": "parent"},
+            ["get", "/v1/parent", {}, {}],
+        ],
+        [
+            [["get", "/v1/{field.sub}", ""]],
+            {"field": {"sub": "parent"}, "foo": "bar"},
+            ["get", "/v1/parent", {}, {"field": {}, "foo": "bar"}],
+        ],
+    ],
+)
+def test_transcode_base_case(http_options, request_kwargs, expected_result):
+    http_options, expected_result = helper_test_transcode(http_options, expected_result)
+    result = path_template.transcode(http_options, **request_kwargs)
+    assert result == expected_result
+
+
+@pytest.mark.parametrize(
+    "http_options, request_kwargs, expected_result",
+    [
+        [
+            [["get", "/v1/{field.subfield}", ""]],
+            {"field": {"subfield": "parent"}, "foo": "bar"},
+            ["get", "/v1/parent", {}, {"field": {}, "foo": "bar"}],
+        ],
+        [
+            [["get", "/v1/{field.subfield.subsubfield}", ""]],
+            {"field": {"subfield": {"subsubfield": "parent"}}, "foo": "bar"},
+            ["get", "/v1/parent", {}, {"field": {"subfield": {}}, "foo": "bar"}],
+        ],
+        [
+            [["get", "/v1/{field.subfield1}/{field.subfield2}", ""]],
+            {"field": {"subfield1": "parent", "subfield2": "child"}, "foo": "bar"},
+            ["get", "/v1/parent/child", {}, {"field": {}, "foo": "bar"}],
+        ],
+    ],
+)
+def test_transcode_subfields(http_options, request_kwargs, expected_result):
+    http_options, expected_result = helper_test_transcode(http_options, expected_result)
+    result = path_template.transcode(http_options, **request_kwargs)
+    assert result == expected_result
+
+
+@pytest.mark.parametrize(
+    "http_options, request_kwargs, expected_result",
+    [
+        # Single segment wildcard
+        [
+            [["get", "/v1/{field=*}", ""]],
+            {"field": "parent"},
+            ["get", "/v1/parent", {}, {}],
+        ],
+        [
+            [["get", "/v1/{field=a/*/b/*}", ""]],
+            {"field": "a/parent/b/child", "foo": "bar"},
+            ["get", "/v1/a/parent/b/child", {}, {"foo": "bar"}],
+        ],
+        # Double segment wildcard
+        [
+            [["get", "/v1/{field=**}", ""]],
+            {"field": "parent/p1"},
+            ["get", "/v1/parent/p1", {}, {}],
+        ],
+        [
+            [["get", "/v1/{field=a/**/b/**}", ""]],
+            {"field": "a/parent/p1/b/child/c1", "foo": "bar"},
+            ["get", "/v1/a/parent/p1/b/child/c1", {}, {"foo": "bar"}],
+        ],
+        # Combined single and double segment wildcard
+        [
+            [["get", "/v1/{field=a/*/b/**}", ""]],
+            {"field": "a/parent/b/child/c1"},
+            ["get", "/v1/a/parent/b/child/c1", {}, {}],
+        ],
+        [
+            [["get", "/v1/{field=a/**/b/*}/v2/{name}", ""]],
+            {"field": "a/parent/p1/b/child", "name": "first", "foo": "bar"},
+            ["get", "/v1/a/parent/p1/b/child/v2/first", {}, {"foo": "bar"}],
+        ],
+    ],
+)
+def test_transcode_with_wildcard(http_options, request_kwargs, expected_result):
+    http_options, expected_result = helper_test_transcode(http_options, expected_result)
+    result = path_template.transcode(http_options, **request_kwargs)
+    assert result == expected_result
+
+
+@pytest.mark.parametrize(
+    "http_options, request_kwargs, expected_result",
+    [
+        # Single field body
+        [
+            [["post", "/v1/no/template", "data"]],
+            {"data": {"id": 1, "info": "some info"}, "foo": "bar"},
+            ["post", "/v1/no/template", {"id": 1, "info": "some info"}, {"foo": "bar"}],
+        ],
+        [
+            [["post", "/v1/{field=a/*}/b/{name=**}", "data"]],
+            {
+                "field": "a/parent",
+                "name": "first/last",
+                "data": {"id": 1, "info": "some info"},
+                "foo": "bar",
+            },
+            [
+                "post",
+                "/v1/a/parent/b/first/last",
+                {"id": 1, "info": "some info"},
+                {"foo": "bar"},
+            ],
+        ],
+        # Wildcard body
+        [
+            [["post", "/v1/{field=a/*}/b/{name=**}", "*"]],
+            {
+                "field": "a/parent",
+                "name": "first/last",
+                "data": {"id": 1, "info": "some info"},
+                "foo": "bar",
+            },
+            [
+                "post",
+                "/v1/a/parent/b/first/last",
+                {"data": {"id": 1, "info": "some info"}, "foo": "bar"},
+                {},
+            ],
+        ],
+    ],
+)
+def test_transcode_with_body(http_options, request_kwargs, expected_result):
+    http_options, expected_result = helper_test_transcode(http_options, expected_result)
+    result = path_template.transcode(http_options, **request_kwargs)
+    assert result == expected_result
+
+
+@pytest.mark.parametrize(
+    "http_options, request_kwargs, expected_result",
+    [
+        # Additional bindings
+        [
+            [
+                ["post", "/v1/{field=a/*}/b/{name=**}", "extra_data"],
+                ["post", "/v1/{field=a/*}/b/{name=**}", "*"],
+            ],
+            {
+                "field": "a/parent",
+                "name": "first/last",
+                "data": {"id": 1, "info": "some info"},
+                "foo": "bar",
+            },
+            [
+                "post",
+                "/v1/a/parent/b/first/last",
+                {"data": {"id": 1, "info": "some info"}, "foo": "bar"},
+                {},
+            ],
+        ],
+        [
+            [
+                ["get", "/v1/{field=a/*}/b/{name=**}", ""],
+                ["get", "/v1/{field=a/*}/b/first/last", ""],
+            ],
+            {"field": "a/parent", "foo": "bar"},
+            ["get", "/v1/a/parent/b/first/last", {}, {"foo": "bar"}],
+        ],
+    ],
+)
+def test_transcode_with_additional_bindings(
+    http_options, request_kwargs, expected_result
+):
+    http_options, expected_result = helper_test_transcode(http_options, expected_result)
+    result = path_template.transcode(http_options, **request_kwargs)
+    assert result == expected_result
+
+
+@pytest.mark.parametrize(
+    "http_options, request_kwargs",
+    [
+        [[["get", "/v1/{name}", ""]], {"foo": "bar"}],
+        [[["get", "/v1/{name}", ""]], {"name": "first/last"}],
+        [[["get", "/v1/{name=mr/*/*}", ""]], {"name": "first/last"}],
+        [[["post", "/v1/{name}", "data"]], {"name": "first/last"}],
+    ],
+)
+def test_transcode_fails(http_options, request_kwargs):
+    http_options, _ = helper_test_transcode(http_options, range(4))
+    with pytest.raises(ValueError):
+        path_template.transcode(http_options, **request_kwargs)
+
+
+def helper_test_transcode(http_options_list, expected_result_list):
+    http_options = []
+    for opt_list in http_options_list:
+        http_option = {"method": opt_list[0], "uri": opt_list[1]}
+        if opt_list[2]:
+            http_option["body"] = opt_list[2]
+        http_options.append(http_option)
+
+    expected_result = {
+        "method": expected_result_list[0],
+        "uri": expected_result_list[1],
+        "query_params": expected_result_list[3],
+    }
+    if expected_result_list[2]:
+        expected_result["body"] = expected_result_list[2]
+
+    return (http_options, expected_result)
diff --git a/tests/unit/test_protobuf_helpers.py b/tests/unit/test_protobuf_helpers.py
new file mode 100644
index 0000000..3df45df
--- /dev/null
+++ b/tests/unit/test_protobuf_helpers.py
@@ -0,0 +1,518 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import sys
+
+import pytest
+
+from google.api import http_pb2
+from google.api_core import protobuf_helpers
+from google.longrunning import operations_pb2
+from google.protobuf import any_pb2
+from google.protobuf import message
+from google.protobuf import source_context_pb2
+from google.protobuf import struct_pb2
+from google.protobuf import timestamp_pb2
+from google.protobuf import type_pb2
+from google.protobuf import wrappers_pb2
+from google.type import color_pb2
+from google.type import date_pb2
+from google.type import timeofday_pb2
+
+
+def test_from_any_pb_success():
+    in_message = date_pb2.Date(year=1990)
+    in_message_any = any_pb2.Any()
+    in_message_any.Pack(in_message)
+    out_message = protobuf_helpers.from_any_pb(date_pb2.Date, in_message_any)
+
+    assert in_message == out_message
+
+
+def test_from_any_pb_wrapped_success():
+    # Declare a message class conforming to wrapped messages.
+    class WrappedDate(object):
+        def __init__(self, **kwargs):
+            self._pb = date_pb2.Date(**kwargs)
+
+        def __eq__(self, other):
+            return self._pb == other
+
+        @classmethod
+        def pb(cls, msg):
+            return msg._pb
+
+    # Run the same test as `test_from_any_pb_success`, but using the
+    # wrapped class.
+    in_message = date_pb2.Date(year=1990)
+    in_message_any = any_pb2.Any()
+    in_message_any.Pack(in_message)
+    out_message = protobuf_helpers.from_any_pb(WrappedDate, in_message_any)
+
+    assert out_message == in_message
+
+
+def test_from_any_pb_failure():
+    in_message = any_pb2.Any()
+    in_message.Pack(date_pb2.Date(year=1990))
+
+    with pytest.raises(TypeError):
+        protobuf_helpers.from_any_pb(timeofday_pb2.TimeOfDay, in_message)
+
+
+def test_check_protobuf_helpers_ok():
+    assert protobuf_helpers.check_oneof() is None
+    assert protobuf_helpers.check_oneof(foo="bar") is None
+    assert protobuf_helpers.check_oneof(foo="bar", baz=None) is None
+    assert protobuf_helpers.check_oneof(foo=None, baz="bacon") is None
+    assert protobuf_helpers.check_oneof(foo="bar", spam=None, eggs=None) is None
+
+
+def test_check_protobuf_helpers_failures():
+    with pytest.raises(ValueError):
+        protobuf_helpers.check_oneof(foo="bar", spam="eggs")
+    with pytest.raises(ValueError):
+        protobuf_helpers.check_oneof(foo="bar", baz="bacon", spam="eggs")
+    with pytest.raises(ValueError):
+        protobuf_helpers.check_oneof(foo="bar", spam=0, eggs=None)
+
+
+def test_get_messages():
+    answer = protobuf_helpers.get_messages(date_pb2)
+
+    # Ensure that Date was exported properly.
+    assert answer["Date"] is date_pb2.Date
+
+    # Ensure that no non-Message objects were exported.
+    for value in answer.values():
+        assert issubclass(value, message.Message)
+
+
+def test_get_dict_absent():
+    with pytest.raises(KeyError):
+        assert protobuf_helpers.get({}, "foo")
+
+
+def test_get_dict_present():
+    assert protobuf_helpers.get({"foo": "bar"}, "foo") == "bar"
+
+
+def test_get_dict_default():
+    assert protobuf_helpers.get({}, "foo", default="bar") == "bar"
+
+
+def test_get_dict_nested():
+    assert protobuf_helpers.get({"foo": {"bar": "baz"}}, "foo.bar") == "baz"
+
+
+def test_get_dict_nested_default():
+    assert protobuf_helpers.get({}, "foo.baz", default="bacon") == "bacon"
+    assert protobuf_helpers.get({"foo": {}}, "foo.baz", default="bacon") == "bacon"
+
+
+def test_get_msg_sentinel():
+    msg = timestamp_pb2.Timestamp()
+    with pytest.raises(KeyError):
+        assert protobuf_helpers.get(msg, "foo")
+
+
+def test_get_msg_present():
+    msg = timestamp_pb2.Timestamp(seconds=42)
+    assert protobuf_helpers.get(msg, "seconds") == 42
+
+
+def test_get_msg_default():
+    msg = timestamp_pb2.Timestamp()
+    assert protobuf_helpers.get(msg, "foo", default="bar") == "bar"
+
+
+def test_invalid_object():
+    with pytest.raises(TypeError):
+        protobuf_helpers.get(object(), "foo", "bar")
+
+
+def test_set_dict():
+    mapping = {}
+    protobuf_helpers.set(mapping, "foo", "bar")
+    assert mapping == {"foo": "bar"}
+
+
+def test_set_msg():
+    msg = timestamp_pb2.Timestamp()
+    protobuf_helpers.set(msg, "seconds", 42)
+    assert msg.seconds == 42
+
+
+def test_set_dict_nested():
+    mapping = {}
+    protobuf_helpers.set(mapping, "foo.bar", "baz")
+    assert mapping == {"foo": {"bar": "baz"}}
+
+
+def test_set_invalid_object():
+    with pytest.raises(TypeError):
+        protobuf_helpers.set(object(), "foo", "bar")
+
+
+def test_set_list():
+    list_ops_response = operations_pb2.ListOperationsResponse()
+
+    protobuf_helpers.set(
+        list_ops_response,
+        "operations",
+        [{"name": "foo"}, operations_pb2.Operation(name="bar")],
+    )
+
+    assert len(list_ops_response.operations) == 2
+
+    for operation in list_ops_response.operations:
+        assert isinstance(operation, operations_pb2.Operation)
+
+    assert list_ops_response.operations[0].name == "foo"
+    assert list_ops_response.operations[1].name == "bar"
+
+
+def test_set_list_clear_existing():
+    list_ops_response = operations_pb2.ListOperationsResponse(
+        operations=[{"name": "baz"}]
+    )
+
+    protobuf_helpers.set(
+        list_ops_response,
+        "operations",
+        [{"name": "foo"}, operations_pb2.Operation(name="bar")],
+    )
+
+    assert len(list_ops_response.operations) == 2
+    for operation in list_ops_response.operations:
+        assert isinstance(operation, operations_pb2.Operation)
+    assert list_ops_response.operations[0].name == "foo"
+    assert list_ops_response.operations[1].name == "bar"
+
+
+def test_set_msg_with_msg_field():
+    rule = http_pb2.HttpRule()
+    pattern = http_pb2.CustomHttpPattern(kind="foo", path="bar")
+
+    protobuf_helpers.set(rule, "custom", pattern)
+
+    assert rule.custom.kind == "foo"
+    assert rule.custom.path == "bar"
+
+
+def test_set_msg_with_dict_field():
+    rule = http_pb2.HttpRule()
+    pattern = {"kind": "foo", "path": "bar"}
+
+    protobuf_helpers.set(rule, "custom", pattern)
+
+    assert rule.custom.kind == "foo"
+    assert rule.custom.path == "bar"
+
+
+def test_set_msg_nested_key():
+    rule = http_pb2.HttpRule(custom=http_pb2.CustomHttpPattern(kind="foo", path="bar"))
+
+    protobuf_helpers.set(rule, "custom.kind", "baz")
+
+    assert rule.custom.kind == "baz"
+    assert rule.custom.path == "bar"
+
+
+def test_setdefault_dict_unset():
+    mapping = {}
+    protobuf_helpers.setdefault(mapping, "foo", "bar")
+    assert mapping == {"foo": "bar"}
+
+
+def test_setdefault_dict_falsy():
+    mapping = {"foo": None}
+    protobuf_helpers.setdefault(mapping, "foo", "bar")
+    assert mapping == {"foo": "bar"}
+
+
+def test_setdefault_dict_truthy():
+    mapping = {"foo": "bar"}
+    protobuf_helpers.setdefault(mapping, "foo", "baz")
+    assert mapping == {"foo": "bar"}
+
+
+def test_setdefault_pb2_falsy():
+    operation = operations_pb2.Operation()
+    protobuf_helpers.setdefault(operation, "name", "foo")
+    assert operation.name == "foo"
+
+
+def test_setdefault_pb2_truthy():
+    operation = operations_pb2.Operation(name="bar")
+    protobuf_helpers.setdefault(operation, "name", "foo")
+    assert operation.name == "bar"
+
+
+def test_field_mask_invalid_args():
+    with pytest.raises(ValueError):
+        protobuf_helpers.field_mask("foo", any_pb2.Any())
+    with pytest.raises(ValueError):
+        protobuf_helpers.field_mask(any_pb2.Any(), "bar")
+    with pytest.raises(ValueError):
+        protobuf_helpers.field_mask(any_pb2.Any(), operations_pb2.Operation())
+
+
+def test_field_mask_equal_values():
+    assert protobuf_helpers.field_mask(None, None).paths == []
+
+    original = struct_pb2.Value(number_value=1.0)
+    modified = struct_pb2.Value(number_value=1.0)
+    assert protobuf_helpers.field_mask(original, modified).paths == []
+
+    original = color_pb2.Color(alpha=wrappers_pb2.FloatValue(value=1.0))
+    modified = color_pb2.Color(alpha=wrappers_pb2.FloatValue(value=1.0))
+    assert protobuf_helpers.field_mask(original, modified).paths == []
+
+    original = struct_pb2.ListValue(values=[struct_pb2.Value(number_value=1.0)])
+    modified = struct_pb2.ListValue(values=[struct_pb2.Value(number_value=1.0)])
+    assert protobuf_helpers.field_mask(original, modified).paths == []
+
+    original = struct_pb2.Struct(fields={"bar": struct_pb2.Value(number_value=1.0)})
+    modified = struct_pb2.Struct(fields={"bar": struct_pb2.Value(number_value=1.0)})
+    assert protobuf_helpers.field_mask(original, modified).paths == []
+
+
+def test_field_mask_zero_values():
+    # Singular Values
+    original = color_pb2.Color(red=0.0)
+    modified = None
+    assert protobuf_helpers.field_mask(original, modified).paths == []
+
+    original = None
+    modified = color_pb2.Color(red=0.0)
+    assert protobuf_helpers.field_mask(original, modified).paths == []
+
+    # Repeated Values
+    original = struct_pb2.ListValue(values=[])
+    modified = None
+    assert protobuf_helpers.field_mask(original, modified).paths == []
+
+    original = None
+    modified = struct_pb2.ListValue(values=[])
+    assert protobuf_helpers.field_mask(original, modified).paths == []
+
+    # Maps
+    original = struct_pb2.Struct(fields={})
+    modified = None
+    assert protobuf_helpers.field_mask(original, modified).paths == []
+
+    original = None
+    modified = struct_pb2.Struct(fields={})
+    assert protobuf_helpers.field_mask(original, modified).paths == []
+
+    # Oneofs
+    original = struct_pb2.Value(number_value=0.0)
+    modified = None
+    assert protobuf_helpers.field_mask(original, modified).paths == []
+
+    original = None
+    modified = struct_pb2.Value(number_value=0.0)
+    assert protobuf_helpers.field_mask(original, modified).paths == []
+
+
+def test_field_mask_singular_field_diffs():
+    original = type_pb2.Type(name="name")
+    modified = type_pb2.Type()
+    assert protobuf_helpers.field_mask(original, modified).paths == ["name"]
+
+    original = type_pb2.Type(name="name")
+    modified = type_pb2.Type()
+    assert protobuf_helpers.field_mask(original, modified).paths == ["name"]
+
+    original = None
+    modified = type_pb2.Type(name="name")
+    assert protobuf_helpers.field_mask(original, modified).paths == ["name"]
+
+    original = type_pb2.Type(name="name")
+    modified = None
+    assert protobuf_helpers.field_mask(original, modified).paths == ["name"]
+
+
+def test_field_mask_message_diffs():
+    original = type_pb2.Type()
+    modified = type_pb2.Type(
+        source_context=source_context_pb2.SourceContext(file_name="name")
+    )
+    assert protobuf_helpers.field_mask(original, modified).paths == [
+        "source_context.file_name"
+    ]
+
+    original = type_pb2.Type(
+        source_context=source_context_pb2.SourceContext(file_name="name")
+    )
+    modified = type_pb2.Type()
+    assert protobuf_helpers.field_mask(original, modified).paths == ["source_context"]
+
+    original = type_pb2.Type(
+        source_context=source_context_pb2.SourceContext(file_name="name")
+    )
+    modified = type_pb2.Type(
+        source_context=source_context_pb2.SourceContext(file_name="other_name")
+    )
+    assert protobuf_helpers.field_mask(original, modified).paths == [
+        "source_context.file_name"
+    ]
+
+    original = None
+    modified = type_pb2.Type(
+        source_context=source_context_pb2.SourceContext(file_name="name")
+    )
+    assert protobuf_helpers.field_mask(original, modified).paths == [
+        "source_context.file_name"
+    ]
+
+    original = type_pb2.Type(
+        source_context=source_context_pb2.SourceContext(file_name="name")
+    )
+    modified = None
+    assert protobuf_helpers.field_mask(original, modified).paths == ["source_context"]
+
+
+def test_field_mask_wrapper_type_diffs():
+    original = color_pb2.Color()
+    modified = color_pb2.Color(alpha=wrappers_pb2.FloatValue(value=1.0))
+    assert protobuf_helpers.field_mask(original, modified).paths == ["alpha"]
+
+    original = color_pb2.Color(alpha=wrappers_pb2.FloatValue(value=1.0))
+    modified = color_pb2.Color()
+    assert protobuf_helpers.field_mask(original, modified).paths == ["alpha"]
+
+    original = color_pb2.Color(alpha=wrappers_pb2.FloatValue(value=1.0))
+    modified = color_pb2.Color(alpha=wrappers_pb2.FloatValue(value=2.0))
+    assert protobuf_helpers.field_mask(original, modified).paths == ["alpha"]
+
+    original = None
+    modified = color_pb2.Color(alpha=wrappers_pb2.FloatValue(value=2.0))
+    assert protobuf_helpers.field_mask(original, modified).paths == ["alpha"]
+
+    original = color_pb2.Color(alpha=wrappers_pb2.FloatValue(value=1.0))
+    modified = None
+    assert protobuf_helpers.field_mask(original, modified).paths == ["alpha"]
+
+
+def test_field_mask_repeated_diffs():
+    original = struct_pb2.ListValue()
+    modified = struct_pb2.ListValue(
+        values=[struct_pb2.Value(number_value=1.0), struct_pb2.Value(number_value=2.0)]
+    )
+    assert protobuf_helpers.field_mask(original, modified).paths == ["values"]
+
+    original = struct_pb2.ListValue(
+        values=[struct_pb2.Value(number_value=1.0), struct_pb2.Value(number_value=2.0)]
+    )
+    modified = struct_pb2.ListValue()
+    assert protobuf_helpers.field_mask(original, modified).paths == ["values"]
+
+    original = None
+    modified = struct_pb2.ListValue(
+        values=[struct_pb2.Value(number_value=1.0), struct_pb2.Value(number_value=2.0)]
+    )
+    assert protobuf_helpers.field_mask(original, modified).paths == ["values"]
+
+    original = struct_pb2.ListValue(
+        values=[struct_pb2.Value(number_value=1.0), struct_pb2.Value(number_value=2.0)]
+    )
+    modified = None
+    assert protobuf_helpers.field_mask(original, modified).paths == ["values"]
+
+    original = struct_pb2.ListValue(
+        values=[struct_pb2.Value(number_value=1.0), struct_pb2.Value(number_value=2.0)]
+    )
+    modified = struct_pb2.ListValue(
+        values=[struct_pb2.Value(number_value=2.0), struct_pb2.Value(number_value=1.0)]
+    )
+    assert protobuf_helpers.field_mask(original, modified).paths == ["values"]
+
+
+def test_field_mask_map_diffs():
+    original = struct_pb2.Struct()
+    modified = struct_pb2.Struct(fields={"foo": struct_pb2.Value(number_value=1.0)})
+    assert protobuf_helpers.field_mask(original, modified).paths == ["fields"]
+
+    original = struct_pb2.Struct(fields={"foo": struct_pb2.Value(number_value=1.0)})
+    modified = struct_pb2.Struct()
+    assert protobuf_helpers.field_mask(original, modified).paths == ["fields"]
+
+    original = None
+    modified = struct_pb2.Struct(fields={"foo": struct_pb2.Value(number_value=1.0)})
+    assert protobuf_helpers.field_mask(original, modified).paths == ["fields"]
+
+    original = struct_pb2.Struct(fields={"foo": struct_pb2.Value(number_value=1.0)})
+    modified = None
+    assert protobuf_helpers.field_mask(original, modified).paths == ["fields"]
+
+    original = struct_pb2.Struct(fields={"foo": struct_pb2.Value(number_value=1.0)})
+    modified = struct_pb2.Struct(fields={"foo": struct_pb2.Value(number_value=2.0)})
+    assert protobuf_helpers.field_mask(original, modified).paths == ["fields"]
+
+    original = struct_pb2.Struct(fields={"foo": struct_pb2.Value(number_value=1.0)})
+    modified = struct_pb2.Struct(fields={"bar": struct_pb2.Value(number_value=1.0)})
+    assert protobuf_helpers.field_mask(original, modified).paths == ["fields"]
+
+
+def test_field_mask_different_level_diffs():
+    original = color_pb2.Color(alpha=wrappers_pb2.FloatValue(value=1.0))
+    modified = color_pb2.Color(alpha=wrappers_pb2.FloatValue(value=2.0), red=1.0)
+    assert sorted(protobuf_helpers.field_mask(original, modified).paths) == [
+        "alpha",
+        "red",
+    ]
+
+
+@pytest.mark.skipif(
+    sys.version_info.major == 2,
+    reason="Field names with trailing underscores can only be created"
+    "through proto-plus, which is Python 3 only.",
+)
+def test_field_mask_ignore_trailing_underscore():
+    import proto
+
+    class Foo(proto.Message):
+        type_ = proto.Field(proto.STRING, number=1)
+        input_config = proto.Field(proto.STRING, number=2)
+
+    modified = Foo(type_="bar", input_config="baz")
+
+    assert sorted(protobuf_helpers.field_mask(None, Foo.pb(modified)).paths) == [
+        "input_config",
+        "type",
+    ]
+
+
+@pytest.mark.skipif(
+    sys.version_info.major == 2,
+    reason="Field names with trailing underscores can only be created"
+    "through proto-plus, which is Python 3 only.",
+)
+def test_field_mask_ignore_trailing_underscore_with_nesting():
+    import proto
+
+    class Bar(proto.Message):
+        class Baz(proto.Message):
+            input_config = proto.Field(proto.STRING, number=1)
+
+        type_ = proto.Field(Baz, number=1)
+
+    modified = Bar()
+    modified.type_.input_config = "foo"
+
+    assert sorted(protobuf_helpers.field_mask(None, Bar.pb(modified)).paths) == [
+        "type.input_config",
+    ]
diff --git a/tests/unit/test_rest_helpers.py b/tests/unit/test_rest_helpers.py
new file mode 100644
index 0000000..5932fa5
--- /dev/null
+++ b/tests/unit/test_rest_helpers.py
@@ -0,0 +1,77 @@
+# Copyright 2021 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import pytest
+
+from google.api_core import rest_helpers
+
+
+def test_flatten_simple_value():
+    with pytest.raises(TypeError):
+        rest_helpers.flatten_query_params("abc")
+
+
+def test_flatten_list():
+    with pytest.raises(TypeError):
+        rest_helpers.flatten_query_params(["abc", "def"])
+
+
+def test_flatten_none():
+    assert rest_helpers.flatten_query_params(None) == []
+
+
+def test_flatten_empty_dict():
+    assert rest_helpers.flatten_query_params({}) == []
+
+
+def test_flatten_simple_dict():
+    assert rest_helpers.flatten_query_params({"a": "abc", "b": "def"}) == [
+        ("a", "abc"),
+        ("b", "def"),
+    ]
+
+
+def test_flatten_repeated_field():
+    assert rest_helpers.flatten_query_params({"a": ["x", "y", "z", None]}) == [
+        ("a", "x"),
+        ("a", "y"),
+        ("a", "z"),
+    ]
+
+
+def test_flatten_nested_dict():
+    obj = {"a": {"b": {"c": ["x", "y", "z"]}}, "d": {"e": "uvw"}}
+    expected_result = [("a.b.c", "x"), ("a.b.c", "y"), ("a.b.c", "z"), ("d.e", "uvw")]
+
+    assert rest_helpers.flatten_query_params(obj) == expected_result
+
+
+def test_flatten_repeated_dict():
+    obj = {
+        "a": {"b": {"c": [{"v": 1}, {"v": 2}]}},
+        "d": "uvw",
+    }
+
+    with pytest.raises(ValueError):
+        rest_helpers.flatten_query_params(obj)
+
+
+def test_flatten_repeated_list():
+    obj = {
+        "a": {"b": {"c": [["e", "f"], ["g", "h"]]}},
+        "d": "uvw",
+    }
+
+    with pytest.raises(ValueError):
+        rest_helpers.flatten_query_params(obj)
diff --git a/tests/unit/test_retry.py b/tests/unit/test_retry.py
new file mode 100644
index 0000000..199ca55
--- /dev/null
+++ b/tests/unit/test_retry.py
@@ -0,0 +1,458 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import datetime
+import itertools
+import re
+
+import mock
+import pytest
+import requests.exceptions
+
+from google.api_core import exceptions
+from google.api_core import retry
+from google.auth import exceptions as auth_exceptions
+
+
+def test_if_exception_type():
+    predicate = retry.if_exception_type(ValueError)
+
+    assert predicate(ValueError())
+    assert not predicate(TypeError())
+
+
+def test_if_exception_type_multiple():
+    predicate = retry.if_exception_type(ValueError, TypeError)
+
+    assert predicate(ValueError())
+    assert predicate(TypeError())
+    assert not predicate(RuntimeError())
+
+
+def test_if_transient_error():
+    assert retry.if_transient_error(exceptions.InternalServerError(""))
+    assert retry.if_transient_error(exceptions.TooManyRequests(""))
+    assert retry.if_transient_error(exceptions.ServiceUnavailable(""))
+    assert retry.if_transient_error(requests.exceptions.ConnectionError(""))
+    assert retry.if_transient_error(requests.exceptions.ChunkedEncodingError(""))
+    assert retry.if_transient_error(auth_exceptions.TransportError(""))
+    assert not retry.if_transient_error(exceptions.InvalidArgument(""))
+
+
+# Make uniform return half of its maximum, which will be the calculated
+# sleep time.
+@mock.patch("random.uniform", autospec=True, side_effect=lambda m, n: n / 2.0)
+def test_exponential_sleep_generator_base_2(uniform):
+    gen = retry.exponential_sleep_generator(1, 60, multiplier=2)
+
+    result = list(itertools.islice(gen, 8))
+    assert result == [1, 2, 4, 8, 16, 32, 60, 60]
+
+
+@mock.patch("time.sleep", autospec=True)
+@mock.patch(
+    "google.api_core.datetime_helpers.utcnow",
+    return_value=datetime.datetime.min,
+    autospec=True,
+)
+def test_retry_target_success(utcnow, sleep):
+    predicate = retry.if_exception_type(ValueError)
+    call_count = [0]
+
+    def target():
+        call_count[0] += 1
+        if call_count[0] < 3:
+            raise ValueError()
+        return 42
+
+    result = retry.retry_target(target, predicate, range(10), None)
+
+    assert result == 42
+    assert call_count[0] == 3
+    sleep.assert_has_calls([mock.call(0), mock.call(1)])
+
+
+@mock.patch("time.sleep", autospec=True)
+@mock.patch(
+    "google.api_core.datetime_helpers.utcnow",
+    return_value=datetime.datetime.min,
+    autospec=True,
+)
+def test_retry_target_w_on_error(utcnow, sleep):
+    predicate = retry.if_exception_type(ValueError)
+    call_count = {"target": 0}
+    to_raise = ValueError()
+
+    def target():
+        call_count["target"] += 1
+        if call_count["target"] < 3:
+            raise to_raise
+        return 42
+
+    on_error = mock.Mock()
+
+    result = retry.retry_target(target, predicate, range(10), None, on_error=on_error)
+
+    assert result == 42
+    assert call_count["target"] == 3
+
+    on_error.assert_has_calls([mock.call(to_raise), mock.call(to_raise)])
+    sleep.assert_has_calls([mock.call(0), mock.call(1)])
+
+
+@mock.patch("time.sleep", autospec=True)
+@mock.patch(
+    "google.api_core.datetime_helpers.utcnow",
+    return_value=datetime.datetime.min,
+    autospec=True,
+)
+def test_retry_target_non_retryable_error(utcnow, sleep):
+    predicate = retry.if_exception_type(ValueError)
+    exception = TypeError()
+    target = mock.Mock(side_effect=exception)
+
+    with pytest.raises(TypeError) as exc_info:
+        retry.retry_target(target, predicate, range(10), None)
+
+    assert exc_info.value == exception
+    sleep.assert_not_called()
+
+
+@mock.patch("time.sleep", autospec=True)
+@mock.patch("google.api_core.datetime_helpers.utcnow", autospec=True)
+def test_retry_target_deadline_exceeded(utcnow, sleep):
+    predicate = retry.if_exception_type(ValueError)
+    exception = ValueError("meep")
+    target = mock.Mock(side_effect=exception)
+    # Setup the timeline so that the first call takes 5 seconds but the second
+    # call takes 6, which puts the retry over the deadline.
+    utcnow.side_effect = [
+        # The first call to utcnow establishes the start of the timeline.
+        datetime.datetime.min,
+        datetime.datetime.min + datetime.timedelta(seconds=5),
+        datetime.datetime.min + datetime.timedelta(seconds=11),
+    ]
+
+    with pytest.raises(exceptions.RetryError) as exc_info:
+        retry.retry_target(target, predicate, range(10), deadline=10)
+
+    assert exc_info.value.cause == exception
+    assert exc_info.match("Deadline of 10.0s exceeded")
+    assert exc_info.match("last exception: meep")
+    assert target.call_count == 2
+
+
+def test_retry_target_bad_sleep_generator():
+    with pytest.raises(ValueError, match="Sleep generator"):
+        retry.retry_target(mock.sentinel.target, mock.sentinel.predicate, [], None)
+
+
+class TestRetry(object):
+    def test_constructor_defaults(self):
+        retry_ = retry.Retry()
+        assert retry_._predicate == retry.if_transient_error
+        assert retry_._initial == 1
+        assert retry_._maximum == 60
+        assert retry_._multiplier == 2
+        assert retry_._deadline == 120
+        assert retry_._on_error is None
+        assert retry_.deadline == 120
+
+    def test_constructor_options(self):
+        _some_function = mock.Mock()
+
+        retry_ = retry.Retry(
+            predicate=mock.sentinel.predicate,
+            initial=1,
+            maximum=2,
+            multiplier=3,
+            deadline=4,
+            on_error=_some_function,
+        )
+        assert retry_._predicate == mock.sentinel.predicate
+        assert retry_._initial == 1
+        assert retry_._maximum == 2
+        assert retry_._multiplier == 3
+        assert retry_._deadline == 4
+        assert retry_._on_error is _some_function
+
+    def test_with_deadline(self):
+        retry_ = retry.Retry(
+            predicate=mock.sentinel.predicate,
+            initial=1,
+            maximum=2,
+            multiplier=3,
+            deadline=4,
+            on_error=mock.sentinel.on_error,
+        )
+        new_retry = retry_.with_deadline(42)
+        assert retry_ is not new_retry
+        assert new_retry._deadline == 42
+
+        # the rest of the attributes should remain the same
+        assert new_retry._predicate is retry_._predicate
+        assert new_retry._initial == retry_._initial
+        assert new_retry._maximum == retry_._maximum
+        assert new_retry._multiplier == retry_._multiplier
+        assert new_retry._on_error is retry_._on_error
+
+    def test_with_predicate(self):
+        retry_ = retry.Retry(
+            predicate=mock.sentinel.predicate,
+            initial=1,
+            maximum=2,
+            multiplier=3,
+            deadline=4,
+            on_error=mock.sentinel.on_error,
+        )
+        new_retry = retry_.with_predicate(mock.sentinel.predicate)
+        assert retry_ is not new_retry
+        assert new_retry._predicate == mock.sentinel.predicate
+
+        # the rest of the attributes should remain the same
+        assert new_retry._deadline == retry_._deadline
+        assert new_retry._initial == retry_._initial
+        assert new_retry._maximum == retry_._maximum
+        assert new_retry._multiplier == retry_._multiplier
+        assert new_retry._on_error is retry_._on_error
+
+    def test_with_delay_noop(self):
+        retry_ = retry.Retry(
+            predicate=mock.sentinel.predicate,
+            initial=1,
+            maximum=2,
+            multiplier=3,
+            deadline=4,
+            on_error=mock.sentinel.on_error,
+        )
+        new_retry = retry_.with_delay()
+        assert retry_ is not new_retry
+        assert new_retry._initial == retry_._initial
+        assert new_retry._maximum == retry_._maximum
+        assert new_retry._multiplier == retry_._multiplier
+
+    def test_with_delay(self):
+        retry_ = retry.Retry(
+            predicate=mock.sentinel.predicate,
+            initial=1,
+            maximum=2,
+            multiplier=3,
+            deadline=4,
+            on_error=mock.sentinel.on_error,
+        )
+        new_retry = retry_.with_delay(initial=5, maximum=6, multiplier=7)
+        assert retry_ is not new_retry
+        assert new_retry._initial == 5
+        assert new_retry._maximum == 6
+        assert new_retry._multiplier == 7
+
+        # the rest of the attributes should remain the same
+        assert new_retry._deadline == retry_._deadline
+        assert new_retry._predicate is retry_._predicate
+        assert new_retry._on_error is retry_._on_error
+
+    def test_with_delay_partial_options(self):
+        retry_ = retry.Retry(
+            predicate=mock.sentinel.predicate,
+            initial=1,
+            maximum=2,
+            multiplier=3,
+            deadline=4,
+            on_error=mock.sentinel.on_error,
+        )
+        new_retry = retry_.with_delay(initial=4)
+        assert retry_ is not new_retry
+        assert new_retry._initial == 4
+        assert new_retry._maximum == 2
+        assert new_retry._multiplier == 3
+
+        new_retry = retry_.with_delay(maximum=4)
+        assert retry_ is not new_retry
+        assert new_retry._initial == 1
+        assert new_retry._maximum == 4
+        assert new_retry._multiplier == 3
+
+        new_retry = retry_.with_delay(multiplier=4)
+        assert retry_ is not new_retry
+        assert new_retry._initial == 1
+        assert new_retry._maximum == 2
+        assert new_retry._multiplier == 4
+
+        # the rest of the attributes should remain the same
+        assert new_retry._deadline == retry_._deadline
+        assert new_retry._predicate is retry_._predicate
+        assert new_retry._on_error is retry_._on_error
+
+    def test___str__(self):
+        def if_exception_type(exc):
+            return bool(exc)  # pragma: NO COVER
+
+        # Explicitly set all attributes as changed Retry defaults should not
+        # cause this test to start failing.
+        retry_ = retry.Retry(
+            predicate=if_exception_type,
+            initial=1.0,
+            maximum=60.0,
+            multiplier=2.0,
+            deadline=120.0,
+            on_error=None,
+        )
+        assert re.match(
+            (
+                r"<Retry predicate=<function.*?if_exception_type.*?>, "
+                r"initial=1.0, maximum=60.0, multiplier=2.0, deadline=120.0, "
+                r"on_error=None>"
+            ),
+            str(retry_),
+        )
+
+    @mock.patch("time.sleep", autospec=True)
+    def test___call___and_execute_success(self, sleep):
+        retry_ = retry.Retry()
+        target = mock.Mock(spec=["__call__"], return_value=42)
+        # __name__ is needed by functools.partial.
+        target.__name__ = "target"
+
+        decorated = retry_(target)
+        target.assert_not_called()
+
+        result = decorated("meep")
+
+        assert result == 42
+        target.assert_called_once_with("meep")
+        sleep.assert_not_called()
+
+    # Make uniform return half of its maximum, which is the calculated sleep time.
+    @mock.patch("random.uniform", autospec=True, side_effect=lambda m, n: n / 2.0)
+    @mock.patch("time.sleep", autospec=True)
+    def test___call___and_execute_retry(self, sleep, uniform):
+
+        on_error = mock.Mock(spec=["__call__"], side_effect=[None])
+        retry_ = retry.Retry(predicate=retry.if_exception_type(ValueError))
+
+        target = mock.Mock(spec=["__call__"], side_effect=[ValueError(), 42])
+        # __name__ is needed by functools.partial.
+        target.__name__ = "target"
+
+        decorated = retry_(target, on_error=on_error)
+        target.assert_not_called()
+
+        result = decorated("meep")
+
+        assert result == 42
+        assert target.call_count == 2
+        target.assert_has_calls([mock.call("meep"), mock.call("meep")])
+        sleep.assert_called_once_with(retry_._initial)
+        assert on_error.call_count == 1
+
+    # Make uniform return half of its maximum, which is the calculated sleep time.
+    @mock.patch("random.uniform", autospec=True, side_effect=lambda m, n: n / 2.0)
+    @mock.patch("time.sleep", autospec=True)
+    def test___call___and_execute_retry_hitting_deadline(self, sleep, uniform):
+
+        on_error = mock.Mock(spec=["__call__"], side_effect=[None] * 10)
+        retry_ = retry.Retry(
+            predicate=retry.if_exception_type(ValueError),
+            initial=1.0,
+            maximum=1024.0,
+            multiplier=2.0,
+            deadline=9.9,
+        )
+
+        utcnow = datetime.datetime.utcnow()
+        utcnow_patcher = mock.patch(
+            "google.api_core.datetime_helpers.utcnow", return_value=utcnow
+        )
+
+        target = mock.Mock(spec=["__call__"], side_effect=[ValueError()] * 10)
+        # __name__ is needed by functools.partial.
+        target.__name__ = "target"
+
+        decorated = retry_(target, on_error=on_error)
+        target.assert_not_called()
+
+        with utcnow_patcher as patched_utcnow:
+            # Make sure that calls to fake time.sleep() also advance the mocked
+            # time clock.
+            def increase_time(sleep_delay):
+                patched_utcnow.return_value += datetime.timedelta(seconds=sleep_delay)
+
+            sleep.side_effect = increase_time
+
+            with pytest.raises(exceptions.RetryError):
+                decorated("meep")
+
+        assert target.call_count == 5
+        target.assert_has_calls([mock.call("meep")] * 5)
+        assert on_error.call_count == 5
+
+        # check the delays
+        assert sleep.call_count == 4  # once between each successive target calls
+        last_wait = sleep.call_args.args[0]
+        total_wait = sum(call_args.args[0] for call_args in sleep.call_args_list)
+
+        assert last_wait == 2.9  # and not 8.0, because the last delay was shortened
+        assert total_wait == 9.9  # the same as the deadline
+
+    @mock.patch("time.sleep", autospec=True)
+    def test___init___without_retry_executed(self, sleep):
+        _some_function = mock.Mock()
+
+        retry_ = retry.Retry(
+            predicate=retry.if_exception_type(ValueError), on_error=_some_function
+        )
+        # check the proper creation of the class
+        assert retry_._on_error is _some_function
+
+        target = mock.Mock(spec=["__call__"], side_effect=[42])
+        # __name__ is needed by functools.partial.
+        target.__name__ = "target"
+
+        wrapped = retry_(target)
+
+        result = wrapped("meep")
+
+        assert result == 42
+        target.assert_called_once_with("meep")
+        sleep.assert_not_called()
+        _some_function.assert_not_called()
+
+    # Make uniform return half of its maximum, which is the calculated sleep time.
+    @mock.patch("random.uniform", autospec=True, side_effect=lambda m, n: n / 2.0)
+    @mock.patch("time.sleep", autospec=True)
+    def test___init___when_retry_is_executed(self, sleep, uniform):
+        _some_function = mock.Mock()
+
+        retry_ = retry.Retry(
+            predicate=retry.if_exception_type(ValueError), on_error=_some_function
+        )
+        # check the proper creation of the class
+        assert retry_._on_error is _some_function
+
+        target = mock.Mock(
+            spec=["__call__"], side_effect=[ValueError(), ValueError(), 42]
+        )
+        # __name__ is needed by functools.partial.
+        target.__name__ = "target"
+
+        wrapped = retry_(target)
+        target.assert_not_called()
+
+        result = wrapped("meep")
+
+        assert result == 42
+        assert target.call_count == 3
+        assert _some_function.call_count == 2
+        target.assert_has_calls([mock.call("meep"), mock.call("meep")])
+        sleep.assert_any_call(retry_._initial)
diff --git a/tests/unit/test_timeout.py b/tests/unit/test_timeout.py
new file mode 100644
index 0000000..30d624e
--- /dev/null
+++ b/tests/unit/test_timeout.py
@@ -0,0 +1,129 @@
+# Copyright 2017 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+import datetime
+import itertools
+
+import mock
+
+from google.api_core import timeout
+
+
+def test__exponential_timeout_generator_base_2():
+    gen = timeout._exponential_timeout_generator(1.0, 60.0, 2.0, deadline=None)
+
+    result = list(itertools.islice(gen, 8))
+    assert result == [1, 2, 4, 8, 16, 32, 60, 60]
+
+
+@mock.patch("google.api_core.datetime_helpers.utcnow", autospec=True)
+def test__exponential_timeout_generator_base_deadline(utcnow):
+    # Make each successive call to utcnow() advance one second.
+    utcnow.side_effect = [
+        datetime.datetime.min + datetime.timedelta(seconds=n) for n in range(15)
+    ]
+
+    gen = timeout._exponential_timeout_generator(1.0, 60.0, 2.0, deadline=30.0)
+
+    result = list(itertools.islice(gen, 14))
+    # Should grow until the cumulative time is > 30s, then start decreasing as
+    # the cumulative time approaches 60s.
+    assert result == [1, 2, 4, 8, 16, 24, 23, 22, 21, 20, 19, 18, 17, 16]
+
+
+class TestConstantTimeout(object):
+    def test_constructor(self):
+        timeout_ = timeout.ConstantTimeout()
+        assert timeout_._timeout is None
+
+    def test_constructor_args(self):
+        timeout_ = timeout.ConstantTimeout(42.0)
+        assert timeout_._timeout == 42.0
+
+    def test___str__(self):
+        timeout_ = timeout.ConstantTimeout(1)
+        assert str(timeout_) == "<ConstantTimeout timeout=1.0>"
+
+    def test_apply(self):
+        target = mock.Mock(spec=["__call__", "__name__"], __name__="target")
+        timeout_ = timeout.ConstantTimeout(42.0)
+        wrapped = timeout_(target)
+
+        wrapped()
+
+        target.assert_called_once_with(timeout=42.0)
+
+    def test_apply_passthrough(self):
+        target = mock.Mock(spec=["__call__", "__name__"], __name__="target")
+        timeout_ = timeout.ConstantTimeout(42.0)
+        wrapped = timeout_(target)
+
+        wrapped(1, 2, meep="moop")
+
+        target.assert_called_once_with(1, 2, meep="moop", timeout=42.0)
+
+
+class TestExponentialTimeout(object):
+    def test_constructor(self):
+        timeout_ = timeout.ExponentialTimeout()
+        assert timeout_._initial == timeout._DEFAULT_INITIAL_TIMEOUT
+        assert timeout_._maximum == timeout._DEFAULT_MAXIMUM_TIMEOUT
+        assert timeout_._multiplier == timeout._DEFAULT_TIMEOUT_MULTIPLIER
+        assert timeout_._deadline == timeout._DEFAULT_DEADLINE
+
+    def test_constructor_args(self):
+        timeout_ = timeout.ExponentialTimeout(1, 2, 3, 4)
+        assert timeout_._initial == 1
+        assert timeout_._maximum == 2
+        assert timeout_._multiplier == 3
+        assert timeout_._deadline == 4
+
+    def test_with_timeout(self):
+        original_timeout = timeout.ExponentialTimeout()
+        timeout_ = original_timeout.with_deadline(42)
+        assert original_timeout is not timeout_
+        assert timeout_._initial == timeout._DEFAULT_INITIAL_TIMEOUT
+        assert timeout_._maximum == timeout._DEFAULT_MAXIMUM_TIMEOUT
+        assert timeout_._multiplier == timeout._DEFAULT_TIMEOUT_MULTIPLIER
+        assert timeout_._deadline == 42
+
+    def test___str__(self):
+        timeout_ = timeout.ExponentialTimeout(1, 2, 3, 4)
+        assert str(timeout_) == (
+            "<ExponentialTimeout initial=1.0, maximum=2.0, multiplier=3.0, "
+            "deadline=4.0>"
+        )
+
+    def test_apply(self):
+        target = mock.Mock(spec=["__call__", "__name__"], __name__="target")
+        timeout_ = timeout.ExponentialTimeout(1, 10, 2)
+        wrapped = timeout_(target)
+
+        wrapped()
+        target.assert_called_with(timeout=1)
+
+        wrapped()
+        target.assert_called_with(timeout=2)
+
+        wrapped()
+        target.assert_called_with(timeout=4)
+
+    def test_apply_passthrough(self):
+        target = mock.Mock(spec=["__call__", "__name__"], __name__="target")
+        timeout_ = timeout.ExponentialTimeout(42.0, 100, 2)
+        wrapped = timeout_(target)
+
+        wrapped(1, 2, meep="moop")
+
+        target.assert_called_once_with(1, 2, meep="moop", timeout=42.0)