def _verify_failure(client, user_agent, url='/'):
    """ Performs a unvalid request and returns associated data.

    :param client: Target client to use for request.
    :param user_agent: Target user agent to use for request.
    :param url: Target unvalid url to request.
    :returns: Request associated response data.
    """
    response = client.get(url, headers={'User-Agent': user_agent})
    assert response.status_code == 404
    return response.data