Agree with whatsit, there are a number of things I see wrong with this. Unit tests built into your app instead of a separate library? Really?   And making your own mock objects? There are about 4 kagillion mocking frameworks out there that are quite fantastic, you're wasting time be creating your own.

Listen, you want info on MVVM and unit testing and all this with WP7, there are a lot better tutorials out there.

http://compiledexperience.com/blog/posts/blendable-mvvm-dependency-injection-and-unit-testing