def test_serverPortIsNativeString(self):
        """
        The C{'SERVER_PORT'} key of the C{environ} C{dict} passed to the
        application is always a native string.
        """
        request, result = self.prepareRequest()
        request.requestReceived()
        result.addCallback(self.environKeyEqual('SERVER_PORT', '80'))
        self.assertIsInstance(self.successResultOf(result), str)

        The C{'SERVER_PORT'} key of the C{environ} C{dict} passed to the
        application is always a native string.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_wsgi.py