def test_argument(self):
        """
        Test that corce correctly raises NotImplementedError.
        """
        arg = formmethod.Argument("name")
        self.assertRaises(NotImplementedError, arg.coerce, "")

        Test that corce correctly raises NotImplementedError.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_formmethod.py