Up to this point, we have tested the service and we have tested the client -- both in isolation. We have written unit tests and our code has good coverage. Unfortunately, my clients are not always synchronous. In Silverlight client, for instance, the framework will not permit you to make synchronous service requests. As it turns out, writing tests for asynchronous service clients is not straight-forward. Thankfully, there are some hacks that you can take advantage of to write effective asynchronous tests.
Testing WCF Service Applications (3 of 4) -- Mocking the Asynchronous Service