def test_initializer(self):
        """
        The header values passed to L{Headers.__init__} can be retrieved via
        L{Headers.getRawHeaders}. If a L{bytes} argument is given, it returns
        L{bytes} values, and if a L{unicode} argument is given, it returns
        L{unicode} values. Both are the same header value, just encoded or
        decoded.
        """
        h = Headers({u'Foo': [u'bar']})
        self.assertEqual(h.getRawHeaders(b'foo'), [b'bar'])
        self.assertEqual(h.getRawHeaders(u'foo'), [u'bar'])

        The header values passed to L{Headers.__init__} can be retrieved via
        L{Headers.getRawHeaders}. If a L{bytes} argument is given, it returns
        L{bytes} values, and if a L{unicode} argument is given, it returns
        L{unicode} values. Both are the same header value, just encoded or
        decoded.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/web/test/test_http_headers.py