'Build a request and then process it using the ``DarkLangMiddleware``.
Args:
language_session_key (str): The language code to set in request.session[LANUGAGE_SESSION_KEY]
accept (str): The accept header to set in request.META[\'HTTP_ACCEPT_LANGUAGE\']'

def process_middleware_request(self, language_session_key=UNSET, accept=UNSET):

    session = {}
    set_if_set(session, LANGUAGE_SESSION_KEY, language_session_key)
    meta = {}
    set_if_set(meta, 'HTTP_ACCEPT_LANGUAGE', accept)
    request = Mock(spec=HttpRequest, session=session, META=meta, GET={}, method='GET', user=self.user)
    self.assertIsNone(DarkLangMiddleware().process_request(request))
    return request
