def test_headersCleanups(self):
        """
        The headers given at initialization should be modified:
        B{proxy-connection} should be removed if present, and B{connection}
        should be added.
        """
        client = ProxyClient(b'GET', b'/foo', b'HTTP/1.0',
            {b"accept": b"text/html", b"proxy-connection": b"foo"}, b'', None)
        self.assertEqual(client.headers,
            {b"accept": b"text/html", b"connection": b"close"})

        The headers given at initialization should be modified:
        B{proxy-connection} should be removed if present, and B{connection}
        should be added.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_proxy.py