def test_applicationProvidedContentType(self):
        """
        If I{Content-Type} is included in the headers passed to the
        I{start_response} callable, one I{Content-Type} header is included in
        the response.
        """
        return self._headersTest(
            [('content-type', 'monkeys are great')],
            [b'Content-Type: monkeys are great'])

        If I{Content-Type} is included in the headers passed to the
        I{start_response} callable, one I{Content-Type} header is included in
        the response.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_wsgi.py