How to use the phonemizer.backend.FestivalBackend function in phonemizer

def _test(text, separator=separator.Separator(
        word=' ', syllable='|', phone='-')):
    backend = FestivalBackend('en-us')
    return backend._phonemize_aux(text, separator, True)

# language_switch option only valid for espeak
    if language_switch != 'keep-flags' and backend != 'espeak':
        raise RuntimeError(
            'the "language_switch" option is available for espeak backend '
            'only, but you are using {} backend'.format(backend))

    # python2 needs additional utf8 encoding
    if sys.version_info[0] == 2:  # pragma: nocover
        logger.warning(
            'Your are using python2 but unsupported by the phonemizer, '
            'please update to python3')

    # instanciate the requested backend for the given language (raises
    # a RuntimeError if the language is not supported).
    backends = {b.name(): b for b in (
        EspeakBackend, FestivalBackend, SegmentsBackend)}

    if backend == 'espeak':
        phonemizer = backends[backend](
            language,
            with_stress=with_stress,
            use_sampa=use_sampa,
            language_switch=language_switch,
            logger=logger)
    else:
        phonemizer = backends[backend](language, logger=logger)

    # phonemize the input text with the backend
    return phonemizer.phonemize(
        text, separator=separator, strip=strip, njobs=njobs)

# version of the phonemizer
    version = (
        'phonemizer-' + pkg_resources.get_distribution('phonemizer').version)

    # for each backend, check if it is available or not. If so get its version
    available = []
    unavailable = []

    if EspeakBackend.is_available():
        available.append(
            'espeak-' + ('ng-' if EspeakBackend.is_espeak_ng() else '')
            + EspeakBackend.version())
    else:  # pragma: nocover
        unavailable.append('espeak')

    if FestivalBackend.is_available():
        available.append('festival-' + FestivalBackend.version())
    else:  # pragma: nocover
        unavailable.append('festival')

    if SegmentsBackend.is_available():
        available.append('segments-' + SegmentsBackend.version())
    else:  # pragma: nocover
        unavailable.append('segments')

    # resumes the backends status in the final version string
    if available:
        version += '\navailable backends: ' + ', '.join(available)
    if unavailable:  # pragma: nocover
        version += '\nuninstalled backends: ' + ', '.join(unavailable)

    return version