@Test public void ptrbuffer04() {

    PtrBuffer pb = make(4,5);
    contains(pb, 2, 4, 6, 8);
    pb.shiftDown(0);
    contains(pb, 4, 6, 8);
    pb.shiftUp(0);
    pb.set(0,1);
    contains(pb, 1, 4, 6, 8);
}