Android Context with SQLite testing

I'm trying to test my SQLite Database but I seem to be a little bit lost between all the different contexts.

my test class extends AndroidTestCase

here is my code :

//Context context = new Activity();

//IsolatedContext context = getMockContext();

//Context context = new MockContext();

//Context context = getInstrumentation().getContext();

  Context context = getContext();

  helper = new MySQLiteHelper(context);
  assertNotNull(helper);

  SQLiteDatabase db = helper.getWritableDatabase();
  assertNotNull(db); <---- it fails here !

as you can see I tried with many different contexts that i saw people use and work with. I really don't understand why it doesn't work in my case.