Update:
Some 10 years later perhaps the best way to test a private method, or any inaccessible member, is via @Jailbreak from the Manifold framework.
@Jailbreak Foo foo = new Foo();
// Direct, *type-safe* access to *all* foo's members
foo.privateMethod(x, y, z);
foo.privateField = value;
This way your code remains type-safe and readable. No design compromises, no overexposing methods and fields for the sake of tests.
If you have somewhat of a legacy Java application, and you're not allowed to change the visibility of your methods, the best way to test private methods is to use reflection.
Internally we're using helpers to get/set private and private static variables as well as invoke private and private static methods. The following patterns will let you do pretty much anything related to the private methods and fields. Of course, you can't change private static final variables through reflection.
Method method = TargetClass.getDeclaredMethod(methodName, argClasses);
method.setAccessible(true);
return method.invoke(targetObject, argObjects);
And for fields:
Field field = TargetClass.getDeclaredField(fieldName);
field.setAccessible(true);
field.set(object, value);
Notes:
1. TargetClass.getDeclaredMethod(methodName, argClasses) lets you look into private methods. The same thing applies for
getDeclaredField.
2. The setAccessible(true) is required to play around with privates.
Best Answer
I think you can completely rely on Robolectric for running your tests in JVM. You get to use JUnit4 for testing your POJOs and Robolectric provides you the support for testing the Android components.
I am also a beginner in TDD for Android Development. I find Robolectric really useful for test driving my code.
This video will tell you almost everything it provides you for unit testing the Android code.
UPDATE: With the Android studio support and the new Android ecosystem, now unit testing can be done as a first class practice. Refer http://developer.android.com/training/testing/unit-testing/local-unit-tests.html for more details.
There are couple of good approaches to test drive the android code. The most effective ones I have found so far is using MVVM(model-view-viewmodel) or MVP(model-view-presenter) approach, where the business logic as well as presentation logic is decoupled from the view and can be easily be unit tested.