def METHOD_NAME(self):
    # no tracks
    ts = TrackSet()
    nt.assert_equal(ts.last_frame(), 0)
    # one track
    t = Track(1)
    t.append(TrackState(1))
    t.append(TrackState(2))
    ts = TrackSet([t])
    nt.assert_equal(ts.last_frame(), 2)
    # two tracks
    t2 = Track(2)
    t2.append(TrackState(3))
    ts = TrackSet([t, t2])
    nt.assert_equal(ts.last_frame(), 3)