def test_readTwice(self):
        """
        Calling L{_InputStream.read} a second time returns bytes starting from
        the position after the last byte returned by the previous read.
        """
        bytes = b"some bytes, hello"
        def read(input):
            input.read(3)
            return input.read()
        d = self._renderAndReturnReaderResult(read, bytes)
        d.addCallback(self.assertEqual, bytes[3:])
        return d

        Calling L{_InputStream.read} a second time returns bytes starting from
        the position after the last byte returned by the previous read.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_wsgi.py