def test_authListing(self):
        """
        L{pop3.POP3} responds to an I{AUTH} command with a list of supported
        authentication types based on its factory's C{challengers}.
        """
        p = DummyPOP3()
        p.factory = internet.protocol.Factory()
        p.factory.challengers = {b'Auth1': None, b'secondAuth': None,
                                 b'authLast': None}
        client = LineSendingProtocol([
            b"AUTH",
            b"QUIT",
        ])

        d = loopback.loopbackAsync(p, client)
        return d.addCallback(self._cbTestAuthListing, client)

        L{pop3.POP3} responds to an I{AUTH} command with a list of supported
        authentication types based on its factory's C{challengers}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_pop3.py