def test_setLastModifiedTwiceNotCached(self):
        """
        When L{http.Request.setLastModified} is called multiple times, the
        highest supplied value is honored. If that value is higher than the
        if-modified-since date in the request header, the method returns None.
        """
        req = http.Request(DummyChannel(), False)
        req.requestHeaders.setRawHeaders(
            networkString('if-modified-since'),
                          [b'01 Jan 1970 00:00:01 GMT']
            )
        req.setLastModified(1000000)

        result = req.setLastModified(0)

        self.assertEqual(result, None)

        When L{http.Request.setLastModified} is called multiple times, the
        highest supplied value is honored. If that value is higher than the
        if-modified-since date in the request header, the method returns None.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_http.py