Update TEST_MAPPING

Test: atest
Change-Id: Ic17afdfd4e0161e0b06bb57f33383f282d051d95
diff --git a/TEST_MAPPING b/TEST_MAPPING
index bbd34fa..339d5b0 100644
--- a/TEST_MAPPING
+++ b/TEST_MAPPING
@@ -1,5 +1,10 @@
 // Generated by update_crate_tests.py for tests that depend on this crate.
 {
+  "imports": [
+    {
+      "path": "external/rust/crates/futures-channel"
+    }
+  ],
   "presubmit": [
     {
       "name": "futures-test_test_src_lib"