Unit test your application

You should start by reading the Testing chapter in the Android documentation.

You may run your tests on a real environment, such as an emulator or a device. However, if you need fast running tests, you should definitely have a look at Robolectric an out-of-container test frameworks that runs within JUnit. It is absolutely needed if you use a continuous test runner, such as infinitest.

For instrumentation / integration tests, have a look at Robotium.