def testSMTPGreetingNotExtended(self):
        """
        Test that the string "ESMTP" does not appear in the SMTP server's
        greeting since that string strongly suggests the presence of support
        for various SMTP extensions which are not supported by L{smtp.SMTP}.
        """
        s = smtp.SMTP()
        t = StringTransport()
        s.makeConnection(t)
        s.connectionLost(error.ConnectionDone())
        self.assertNotIn(b"ESMTP", t.value())

        Test that the string "ESMTP" does not appear in the SMTP server's
        greeting since that string strongly suggests the presence of support
        for various SMTP extensions which are not supported by L{smtp.SMTP}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_smtp.py