Add test for new __ne__ method on Promise.

        # check that it behaves like a property when there's no instance

        self.assertIsInstance(A.value, cached_property)

    def test_lazy_equality(self):

        """

        Tests that == and != work correctly for Promises.

        """

        lazy_a = lazy(lambda: 4, int)

        lazy_b = lazy(lambda: 4, int)

        lazy_c = lazy(lambda: 5, int)

        self.assertEqual(lazy_a(), lazy_b())

        self.assertNotEqual(lazy_b(), lazy_c())