def rename_track(track, pattern):
supported_fields = track.supported_fields()
fields = {field: getattr(track, field) for field in supported_fields}
name = pattern.format(**fields) + extension(track.path)
destination = os.path.join(parent(track.path), name)
shutil.move(track.path, destination)
track.path = destination
def test_extension():
assert library.extension(path_file) == '.ext'