What's a good unit testing assignment for Android? I'm teaching a capstone (the final class in an undergraduate program) software engineering course in which we are developing Android applications in Java. I consider test-driven development and unit testing important but am having trouble coming up with Android-related assignments, since so much mobile programming is about user interfaces and synchronization, neither of which are ideal for unit testing.

The only thing I've thought of is that they could unit test a database running on Android, which would also let me introduce mocking, but that doesn't sound very interesting.

Any suggestions of a small but interesting Android project suitable to TDD and unit testing?
I assume that there is some logic in the app, somewhere. Hard for me to imagine it otherwise. 

If you build the client side with a Model-View-Controller architecture, the testing can be done on the model (as is most natural) and possibly on the controller. 

If the server side is also built by the students, then it may also require logic beyond data access. So that can also be tested, either directly on the server side, or with mock clients. Maybe both. 

I admit, though, that I don't build these things.