def test_openForReading(self):
        """
        Check that openForReading returns an object providing C{ftp.IReadFile}.
        """
        self.createFile('file.txt')
        d = self.shell.openForReading(('file.txt',))
        def cb(res):
            self.assertTrue(ftp.IReadFile.providedBy(res))
        d.addCallback(cb)
        return d

        Check that openForReading returns an object providing C{ftp.IReadFile}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/test/test_ftp.py