@Test public void ptrbuffer03() {

    PtrBuffer pb = make(4,5);
    contains(pb, 2, 4, 6, 8);
    pb.shiftUp(0);
    pb.set(0, 99);
    contains(pb, 99, 2, 4, 6, 8);
    pb.shiftDown(0);
    contains(pb, 2, 4, 6, 8);
}