def METHOD_NAME():
    """Build the charmcraft's user agent."""
    if any(key.startswith(prefix) for prefix in TESTING_ENV_PREFIXES for key in os.environ):
        testing = " (testing) "
    else:
        testing = " "
    os_platform = "{0.system}/{0.release} ({0.machine})".format(utils.get_os_platform())
    return "charmcraft/{}{}{} python/{}".format(
        __version__, testing, os_platform, platform.python_version()
    )