def test_anonymousWriteDenied(self):
        """
        When an anonymous user attempts to edit the server-side filesystem, they
        will receive a 550 error with a descriptive message.

        @return: L{Deferred} of command response
        """
        d = self._anonymousLogin()
        return self.assertCommandFailed(
              'MKD newdir',
              ['550 Anonymous users are forbidden to change the filesystem'],
              chainDeferred=d)

        When an anonymous user attempts to edit the server-side filesystem, they
        will receive a 550 error with a descriptive message.

        @return: L{Deferred} of command response
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_ftp.py