def setUp(self):
        """
        Create an L{_IdentityTransferDecoder} with callbacks hooked up so that
        calls to them can be inspected.
        """
        self.data = []
        self.finish = []
        self.contentLength = 10
        self.decoder = _IdentityTransferDecoder(
            self.contentLength, self.data.append, self.finish.append)

        Create an L{_IdentityTransferDecoder} with callbacks hooked up so that
        calls to them can be inspected.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_http.py