The thing that changed my approach to testing, at least in OO languages, was being shown that use cases/tasks/"things the system can do" should be first class objects in the model. At that point, you have a single layer that exposes everything of real value in the application, giving you a really simple test surface. Underneath that surface you can refactor to your heart's delight, without worrying about having to maintain lots of pointless unit tests for trivial behaviours on each object - all that matters is maintaining the end to end functionality. So yes, I agree integration tests are the key, and you can architect your application to make this easier. Not over-testing your underlying model is just good old fashioned information-hiding. Testing the UI on top I leave as a matter of taste.