@Test public void ptrbuffer05() {

    PtrBuffer pb = make(4,5);
    contains(pb, 2, 4, 6, 8);
    pb.shiftUp(2);
    pb.set(2, 0);
    contains(pb, 2, 4, 0, 6, 8);
    pb.shiftDown(2);
    contains(pb, 2, 4, 6, 8);
}