There are some cases where you really need to test parts of the application in isolation with little connection to the underlying system. In Android, the system is the Activity framework. In such cases, we have to select a base class that is high enough in the test hierarchy to remove some of the dependencies but not high enough for us to be responsible for some of the basic infrastructure of instantiating Context, for example.

In such cases, the candidate base class is AndroidTestCase because this allows the use of Context and Resources without thinking about Activities:

public class AccessPrivateDataTest extends AndroidTestCase {

   public void testAccessAnotherAppsPrivateDataIsNotPossible()  {
        String filesDirectory = getContext().getFilesDir().getPath();
        String privateFilePath = filesDirectory + 
"/data/com.android.cts.appwithdata/private_file.txt";
        try {
            new FileInputStream(privateFilePath);
            fail("Was able to access another...