def test_startTLS(self):
        """
        L{IMAP4Client.startTLS} triggers TLS negotiation and returns a
        L{Deferred} which fires after the client's transport is using
        encryption.
        """
        disconnected = self.startTLSAndAssertSession()
        self.connected.addCallback(self._cbStopClient)
        self.connected.addErrback(self._ebGeneral)
        return disconnected

        L{IMAP4Client.startTLS} triggers TLS negotiation and returns a
        L{Deferred} which fires after the client's transport is using
        encryption.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_imap.py