def test_callable(self):
        """
        Tests must be callable in order to be used with Python's unittest.py.
        """
        self.assertTrue(callable(self.test),
                        "%r is not callable." % (self.test,))

        Tests must be callable in order to be used with Python's unittest.py.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/trial/test/test_pyunitcompat.py