def test_difference_update_with_no_arguments(self):
        python_set = set([1, 2, 3])
        python_set.difference_update()

        ts = TraitSet([1, 2, 3])
        ts.difference_update()

        self.assertEqual(ts, python_set)
 def test_difference_update_varargs(self):
     ts = TraitSet([1, 2, 3], notifiers=[self.notification_handler])
     ts.difference_update([2], [3])
     self.assertEqual(self.removed, {2, 3})