How to use the spotdl.youtube_tools.download_song function in spotdl

def test_m4a(self, monkeypatch, filename_fixture):
        expect_download = True
        monkeypatch.setattr(
            "pafy.backend_shared.BaseStream.download", self.blank_audio_generator
        )
        monkeypatch.setattr(
            "pafy.backend_youtube_dl.YtdlStream.download", self.blank_audio_generator
        )
        download = youtube_tools.download_song(
            filename_fixture + ".m4a", pytest.content_fixture
        )
        assert download == expect_download

def test_m4a(self):
        expect_download = True
        download = youtube_tools.download_song(file_name + ".m4a", content)
        assert download == expect_download

def test_other(self, content_fixture, filename_fixture, monkeypatch):
        expect_download = False
        monkeypatch.setattr("pafy.backend_shared.BaseStream.download", lambda x: None)
        download = youtube_tools.download_song(
            filename_fixture + ".fake_extension", content_fixture
        )
        assert download == expect_download

def test_webm(self, monkeypatch, filename_fixture):
        expect_download = True
        monkeypatch.setattr(
            "pafy.backend_shared.BaseStream.download", self.blank_audio_generator
        )
        monkeypatch.setattr(
            "pafy.backend_youtube_dl.YtdlStream.download", self.blank_audio_generator
        )
        download = youtube_tools.download_song(
            filename_fixture + ".webm", pytest.content_fixture
        )
        assert download == expect_download

def test_webm(self, content_fixture, filename_fixture, monkeypatch):
        # content_fixture does not have any .webm audiostream
        expect_download = False
        monkeypatch.setattr("pafy.backend_shared.BaseStream.download", lambda x: None)
        download = youtube_tools.download_song(
            filename_fixture + ".webm", content_fixture
        )
        assert download == expect_download

def test_webm(self, content_fixture, filename_fixture, monkeypatch):
        # content_fixture does not have any .webm audiostream
        expect_download = False
        monkeypatch.setattr("pafy.backend_shared.BaseStream.download", lambda x: None)
        download = youtube_tools.download_song(
            filename_fixture + ".webm", content_fixture
        )
        assert download == expect_download

def _download_single(self, songname):
        # deal with file formats containing slashes to non-existent directories
        songpath = os.path.join(const.args.folder, os.path.dirname(songname))
        os.makedirs(songpath, exist_ok=True)
        input_song = songname + const.args.input_ext
        output_song = songname + const.args.output_ext
        if youtube_tools.download_song(input_song, self.content):
            print("")
            try:
                convert.song(
                    input_song,
                    output_song,
                    const.args.folder,
                    avconv=const.args.avconv,
                    trim_silence=const.args.trim_silence,
                    delete_original=not const.args.no_remove_original,
                )
            except FileNotFoundError:
                encoder = "avconv" if const.args.avconv else "ffmpeg"
                log.warning("Could not find {0}, skip encoding".format(encoder))
                output_song = self.unconverted_filename(songname)

            if not const.args.no_metadata and self.meta_tags is not None: