def test_stdioTransport(self):
        """
        The I{-bs} option for using stdin and stdout as the SMTP transport
        is unsupported and if it is passed to L{parseOptions}, L{SystemExit}
        is raised.
        """
        exc = self.assertRaises(SystemExit, parseOptions, ['-bs'])
        self.assertEqual(exc.args, ("Unsupported option.",))

        The I{-bs} option for using stdin and stdout as the SMTP transport
        is unsupported and if it is passed to L{parseOptions}, L{SystemExit}
        is raised.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_mailmail.py