def test_exactAmountReceived(self):
        """
        If L{_IdentityTransferDecoder.dataReceived} is called with a byte string
        with length equal to the content length passed to
        L{_IdentityTransferDecoder}'s initializer, the data callback is invoked
        with that string and the finish callback is invoked with a zero-length
        string.
        """
        self.decoder.dataReceived(b'x' * self.contentLength)
        self.assertEqual(self.data, [b'x' * self.contentLength])
        self.assertEqual(self.finish, [b''])

        If L{_IdentityTransferDecoder.dataReceived} is called with a byte string
        with length equal to the content length passed to
        L{_IdentityTransferDecoder}'s initializer, the data callback is invoked
        with that string and the finish callback is invoked with a zero-length
        string.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_http.py