src/matchers/has_entry_matcher.rs

// Copyright 2022 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.

use crate::description::Description;
use crate::matcher::{Matcher, MatcherResult};
use std::collections::HashMap;
use std::fmt::Debug;
use std::hash::Hash;
use std::marker::PhantomData;

/// Matches a HashMap containing the given `key` whose value is matched by the
/// matcher `inner`.
///
/// ```
/// # use googletest::prelude::*;
/// # use std::collections::HashMap;
/// # fn should_pass() -> Result<()> {
/// let value = HashMap::from([(0, 1), (1, -1)]);
/// verify_that!(value, has_entry(0, eq(1)))?;  // Passes
/// #     Ok(())
/// # }
/// # fn should_fail_1() -> Result<()> {
/// # let value = HashMap::from([(0, 1), (1, -1)]);
/// verify_that!(value, has_entry(1, gt(0)))?;  // Fails: value not matched
/// #     Ok(())
/// # }
/// # fn should_fail_2() -> Result<()> {
/// # let value = HashMap::from([(0, 1), (1, -1)]);
/// verify_that!(value, has_entry(2, eq(0)))?;  // Fails: key not present
/// #     Ok(())
/// # }
/// # should_pass().unwrap();
/// # should_fail_1().unwrap_err();
/// # should_fail_2().unwrap_err();
/// ```
///
/// Note: One could obtain the same effect by collecting entries into a `Vec`
/// and using `contains`:
///
/// ```
/// # use googletest::prelude::*;
/// # use std::collections::HashMap;
/// # fn should_pass() -> Result<()> {
/// let value = HashMap::from([(0, 1), (1, -1)]);
/// verify_that!(value.into_iter().collect::<Vec<_>>(), contains(eq((0, 1))))?;
/// #     Ok(())
/// # }
/// # should_pass().unwrap();
/// ```
///
/// However, `has_entry` will offer somewhat better diagnostic messages in the
/// case of assertion failure. And it avoid the extra allocation hidden in the
/// code above.
pub fn has_entry<KeyT: Debug + Eq + Hash, ValueT: Debug, MatcherT: Matcher<ActualT = ValueT>>(
    key: KeyT,
    inner: MatcherT,
) -> impl Matcher<ActualT = HashMap<KeyT, ValueT>> {
    HasEntryMatcher { key, inner, phantom: Default::default() }
}

struct HasEntryMatcher<KeyT, ValueT, MatcherT> {
    key: KeyT,
    inner: MatcherT,
    phantom: PhantomData<ValueT>,
}

impl<KeyT: Debug + Eq + Hash, ValueT: Debug, MatcherT: Matcher<ActualT = ValueT>> Matcher
    for HasEntryMatcher<KeyT, ValueT, MatcherT>
{
    type ActualT = HashMap<KeyT, ValueT>;

    fn matches(&self, actual: &HashMap<KeyT, ValueT>) -> MatcherResult {
        if let Some(value) = actual.get(&self.key) {
            self.inner.matches(value)
        } else {
            MatcherResult::NoMatch
        }
    }

    fn explain_match(&self, actual: &HashMap<KeyT, ValueT>) -> Description {
        if let Some(value) = actual.get(&self.key) {
            format!(
                "which contains key {:?}, but is mapped to value {:#?}, {}",
                self.key,
                value,
                self.inner.explain_match(value)
            )
            .into()
        } else {
            format!("which doesn't contain key {:?}", self.key).into()
        }
    }

    fn describe(&self, matcher_result: MatcherResult) -> Description {
        match matcher_result {
            MatcherResult::Match => format!(
                "contains key {:?}, which value {}",
                self.key,
                self.inner.describe(MatcherResult::Match)
            )
            .into(),
            MatcherResult::NoMatch => format!(
                "doesn't contain key {:?} or contains key {:?}, which value {}",
                self.key,
                self.key,
                self.inner.describe(MatcherResult::NoMatch)
            )
            .into(),
        }
    }
}

#[cfg(test)]
mod tests {
    use super::has_entry;
    use crate::prelude::*;
    use indoc::indoc;
    use std::collections::HashMap;

    #[test]
    fn has_entry_does_not_match_empty_hash_map() -> Result<()> {
        let value: HashMap<i32, i32> = HashMap::new();
        verify_that!(value, not(has_entry(0, eq(0))))
    }

    #[test]
    fn has_entry_matches_hash_map_with_value() -> Result<()> {
        let value: HashMap<i32, i32> = HashMap::from([(0, 0)]);
        verify_that!(value, has_entry(0, eq(0)))
    }

    #[test]
    fn has_entry_does_not_match_hash_map_with_wrong_value() -> Result<()> {
        let value: HashMap<i32, i32> = HashMap::from([(0, 1)]);
        verify_that!(value, not(has_entry(0, eq(0))))
    }

    #[test]
    fn has_entry_does_not_match_hash_map_with_wrong_key() -> Result<()> {
        let value: HashMap<i32, i32> = HashMap::from([(1, 0)]);
        verify_that!(value, not(has_entry(0, eq(0))))
    }

    #[test]
    fn has_entry_shows_correct_message_when_key_is_not_present() -> Result<()> {
        let result = verify_that!(HashMap::from([(0, 0)]), has_entry(1, eq(0)));

        verify_that!(
            result,
            err(displays_as(contains_substring(indoc!(
                "
                Value of: HashMap::from([(0, 0)])
                Expected: contains key 1, which value is equal to 0
                Actual: {0: 0},
                  which doesn't contain key 1
                "
            ))))
        )
    }

    #[test]
    fn has_entry_shows_correct_message_when_key_has_non_matching_value() -> Result<()> {
        let result = verify_that!(HashMap::from([(0, 0)]), has_entry(0, eq(1)));

        verify_that!(
            result,
            err(displays_as(contains_substring(indoc!(
                "
                Value of: HashMap::from([(0, 0)])
                Expected: contains key 0, which value is equal to 1
                Actual: {0: 0},
                  which contains key 0, but is mapped to value 0, which isn't equal to 1
                "
            ))))
        )
    }
}