def test_strWithNegativeCode(self):
        """
        If the response code supplied to L{SMTPClientError} is negative, it
        is excluded from the string representation.
        """
        err = smtp.SMTPClientError(-1, b"foo bar")
        self.assertEqual(str(err), "foo bar")

        If the response code supplied to L{SMTPClientError} is negative, it
        is excluded from the string representation.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_smtp.py