def setUp(self):
        """
        Set up a POP3 server with virtual domain support.
        """
        self.factory = internet.protocol.Factory()
        self.factory.domains = {}
        self.factory.domains[b'baz.com'] = DummyDomain()
        self.factory.domains[b'baz.com'].addUser(b'hello')
        self.factory.domains[b'baz.com'].addMessage(b'hello', self.message)

        Set up a POP3 server with virtual domain support.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_pop3.py