def test_existingRemoteDirectory(self):
        """
        Test that a C{mkdir} on an existing directory fails with the
        appropriate error, and doesn't log an useless error server side.
        """
        def _check(results):
            self.assertEqual(results[0], b'')
            self.assertEqual(results[1],
                              b'remote error 11: mkdir failed')

        d = self.runScript('mkdir testMakeDirectory',
                           'mkdir testMakeDirectory')
        d.addCallback(_check)
        return d

        Test that a C{mkdir} on an existing directory fails with the
        appropriate error, and doesn't log an useless error server side.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/conch/test/test_cftp.py