def test_tagWithoutLocation(self):
        """
        If a L{FlattenerError} is created with a L{Tag} instance without source
        location information, only the tagName is included in the string
        representation of the exception.
        """
        self.assertEqual(
            str(FlattenerError(RuntimeError("reason"), [Tag('span')], [])),
            "Exception while flattening:\n"
            "  Tag <span>\n"
            "RuntimeError: reason\n")

        If a L{FlattenerError} is created with a L{Tag} instance without source
        location information, only the tagName is included in the string
        representation of the exception.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_flatten.py