def METHOD_NAME(self):
    test = List([1, 2, 3])
    test += [4, 5, 6]
    self.assertIsInstance(test, List)
    self.assertEqual(test, [1, 2, 3, 4, 5, 6])
    test = test + [7, 8]
    self.assertIsInstance(test, List)
    self.assertEqual(test, [1, 2, 3, 4, 5, 6, 7, 8])