def METHOD_NAME(self):
    pl_lib = self.library.playlists
    pl = pl_lib.create("playlist1")
    pl.extend(NUMERIC_SONGS)
    playlists = pl_lib.playlists_featuring(NUMERIC_SONGS[0])
    assert set(playlists) == {pl}
    # Now add a second one, check that instance tracking works
    pl2 = pl_lib.create("playlist2")
    pl2.append(NUMERIC_SONGS[0])
    playlists = pl_lib.playlists_featuring(NUMERIC_SONGS[0])
    assert set(playlists) == {pl, pl2}, "didn't register playlist2"
    assert set(pl_lib.playlists_featuring(NUMERIC_SONGS[1])) == {pl}