def test_contentLength(self):
        """
        The C{'CONTENT_LENGTH'} key of the C{environ} C{dict} passed to the
        application contains the value of the I{Content-Length} request header
        (RFC 3875, section 4.1.2).
        """
        missing = self.render('GET', '1.1', [], [''])
        missing.addCallback(self.environKeyEqual('CONTENT_LENGTH', ''))

        present = self.render(
            'GET', '1.1', [], [''], None, [('content-length', '1234')])
        present.addCallback(self.environKeyEqual('CONTENT_LENGTH', '1234'))

        return gatherResults([missing, present])

        The C{'CONTENT_LENGTH'} key of the C{environ} C{dict} passed to the
        application contains the value of the I{Content-Length} request header
        (RFC 3875, section 4.1.2).
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_wsgi.py