def test_identity(self):
        """
        Instances of a class which mixes in L{FancyEqMixin} but which
        defines no comparison attributes compare by identity.
        """
        class Empty(util.FancyEqMixin):
            pass

        self.assertFalse(Empty() == Empty())
        self.assertTrue(Empty() != Empty())
        empty = Empty()
        self.assertTrue(empty == empty)
        self.assertFalse(empty != empty)

        Instances of a class which mixes in L{FancyEqMixin} but which
        defines no comparison attributes compare by identity.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_util.py