How to use the pytube.extract.js_url function in pytube

def test_js_url(cipher_signature):
    expected = 'https://youtube.com/yts/jsbin/player-vflOdyxa4/en_US/base.js'
    result = extract.js_url(cipher_signature.watch_html)
    assert expected == result

"""
        self.watch_html = request.get(url=self.watch_url)
        if '

"""
        self.watch_html = request.get(url=self.watch_url)
        if '

self.vid_descr = extract.get_vid_descr(self.watch_html)
        # https://github.com/nficano/pytube/issues/165
        stream_maps = ['url_encoded_fmt_stream_map']
        if 'adaptive_fmts' in self.player_config_args:
            stream_maps.append('adaptive_fmts')

        # unscramble the progressive and adaptive stream manifests.
        for fmt in stream_maps:
            if not self.age_restricted and fmt in self.vid_info:
                mixins.apply_descrambler(self.vid_info, fmt)
            mixins.apply_descrambler(self.player_config_args, fmt)

            try:
                mixins.apply_signature(self.player_config_args, fmt, self.js)
            except TypeError:
                self.js_url = extract.js_url(
                    self.embed_html, self.age_restricted,
                )
                self.js = request.get(self.js_url)
                mixins.apply_signature(self.player_config_args, fmt, self.js)

            # build instances of :class:`Stream `
            self.initialize_stream_objects(fmt)

        # load the player_response object (contains subtitle information)
        apply_mixin(self.player_config_args, 'player_response', json.loads)

        self.initialize_caption_objects()
        logger.info('init finished successfully')

self.vid_descr = extract.get_vid_descr(self.watch_html)
        # https://github.com/nficano/pytube/issues/165
        stream_maps = ['url_encoded_fmt_stream_map']
        if 'adaptive_fmts' in self.player_config_args:
            stream_maps.append('adaptive_fmts')

        # unscramble the progressive and adaptive stream manifests.
        for fmt in stream_maps:
            if not self.age_restricted and fmt in self.vid_info:
                mixins.apply_descrambler(self.vid_info, fmt)
            mixins.apply_descrambler(self.player_config_args, fmt)

            try:
                mixins.apply_signature(self.player_config_args, fmt, self.js)
            except TypeError:
                self.js_url = extract.js_url(
                    self.embed_html, self.age_restricted,
                )
                self.js = request.get(self.js_url)
                mixins.apply_signature(self.player_config_args, fmt, self.js)

            # build instances of :class:`Stream `
            self.initialize_stream_objects(fmt)

        # load the player_response object (contains subtitle information)
        apply_mixin(self.player_config_args, 'player_response', json.loads)

        self.initialize_caption_objects()
        logger.info('init finished successfully')

"""
		self.watch_html = request.get(url=self.watch_url)
		if '