* break the invariants. Sometimes we need to bubble an element up instead of trickling down. See
   * implementation.
   */
  public void testInvalidatingRemove() {
    MinMaxPriorityQueue<Integer> mmHeap = MinMaxPriorityQueue.create();
    mmHeap.addAll(
        Lists.newArrayList(1, 20, 1000, 2, 3, 30, 40, 10, 11, 12, 13, 300, 400, 500, 600));