if you plan to test the logic of the class (methods, functions), then the flag is in your hands, because unit testing is what it is for. And using Mocks, you can safely isolate your class from data providers and completely cover it with tests. How does the WCF participate here, I do not understand. And again, even if you plan to write integration tests, then they will need to describe their client to WCF services, which again is not justified because there is no point in testing the tests (I apologize for the pun). It is more correct to make test coverage of the client separately locked up the calls to the services, and having isolated the services accordingly from its data providers. I hope I explained quite extensively. The comment did not fit, let it be the answer :).