There is a reason mocking is not supported: It's incredibly error prone. The previous version of gRPC (Stubby) did actually support mocking of the stub/service

There is a reason mocking is not supported: It's incredibly error prone. The previous version of gRPC (Stubby) did actually support mocking of the stub/service interfaces. The issue is that people mock out responses that don't map to reality, causing the tests to pass but the system-under-test to blow up. This happened often enough that ability to mock was ripped out, and the InProcess server-client added. The extra "jibber-jabber" is what makes people confident that their Stub usage is correct. Some sample bugs NOT caught by a mock: * Calling the stub with a NULL message * Not calling close() * Sending invalid headers * Ignoring deadlines * Ignoring cancellation There's more, but these are real bugs that are trivially caught by using a real (and cheap) server.