@Test public void ptrbuffer07() {

    PtrBuffer pb = make(4,5);
    contains(pb, 2, 4, 6, 8);
    pb.shiftUp(3);
    pb.set(3, 1);
    contains(pb, 2, 4, 6, 1, 8);
    pb.shiftDown(3);
    contains(pb, 2, 4, 6, 8);
}