def test_responseWithNoMessage(self):
        """
        Responses with no message are still valid, i.e. three digits
        followed by a space is complete response.
        """
        ftpClient = ftp.FTPClientBasic()
        ftpClient.lineReceived(b'220 ')
        self.assertEqual(['220 '], ftpClient.greeting)

        Responses with no message are still valid, i.e. three digits
        followed by a space is complete response.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_ftp.py