public static TrackPair of(Track track1, Track track2) {
        return new TrackPair(track1, track2);
    }
@Test
    public void testOf() {

        Track<NopHit> track1 = Track.of(newArrayList(P1, P2, P3));
        Track<NopHit> track2 = Track.of(newArrayList(P4, P5, P6));

        TrackPair pair = TrackPair.of(track1, track2);
        assertEquals(pair.track1(), track1);
        assertEquals(pair.track2(), track2);
    }