https://source.cloud.google.com/results/invocations/ed4b146d-d229-46e4-9fd7-5f1c271d9e2c/targets/github%2Fgrpc%2Frun_tests%2Fpython_macos_opt_native%2Fpy36_native.test.unit._metadata_flags_test.MetadataFlagsTest/tests