def test_unknownContentLength(self):
        """
        If L{_IdentityTransferDecoder} is constructed with L{None} for the
        content length, it passes all data delivered to it through to the data
        callback.
        """
        data = []
        finish = []
        decoder = _IdentityTransferDecoder(None, data.append, finish.append)
        decoder.dataReceived(b'x')
        self.assertEqual(data, [b'x'])
        decoder.dataReceived(b'y')
        self.assertEqual(data, [b'x', b'y'])
        self.assertEqual(finish, [])

        If L{_IdentityTransferDecoder} is constructed with L{None} for the
        content length, it passes all data delivered to it through to the data
        callback.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_http.py