The tests for the various components of the gRPC transport implementation live in the test_fixtures.h header and in the various tests themselves. The bits about setting up a GRPCTransportLayer with basic ingress/egress behavior in particular ought to be shared among the various tests that use it. Furthermore, it should be more cleanly separated from the existing CommandServiceTestFixtures (whose name should probably drop the final "s" given that it inherits from unittest::Test), which is mean to test the more low-level CommandService gRPC service.