def test_environIsDict(self):
        """
        L{WSGIResource} calls the application object with an C{environ}
        parameter which is exactly of type C{dict}.
        """
        d = self.render('GET', '1.1', [], [''])
        def cbRendered(result):
            environ, startResponse = result
            self.assertIdentical(type(environ), dict)
            # Environment keys are always native strings.
            for name in environ:
                self.assertIsInstance(name, str)
        d.addCallback(cbRendered)
        return d

        L{WSGIResource} calls the application object with an C{environ}
        parameter which is exactly of type C{dict}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_wsgi.py