def test_serializeSameDeferredTwice(self):
        """
        Test that the same deferred can be flattened twice.
        """
        d = succeed('three')
        return gatherResults([
            self.assertFlattensTo(d, b'three'),
            self.assertFlattensTo(d, b'three'),
        ])

        Test that the same deferred can be flattened twice.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_flatten.py