}
      // bubble it up the opposite heap
      if (otherHeap.bubbleUpAlternatingLevels(crossOver, toTrickle) < removeIndex) {
        return new MoveDesc<>(toTrickle, parent);
      } else {
        return null;
      }
    }

    /** Bubbles a value from {@code index} up the appropriate heap if required. */
    void bubbleUp(int index, E x) {
      int crossOver = crossOverUp(index, x);

  /**
   * Catches a bug where when constructing a service manager failed, later interactions with the
   * service could cause IllegalStateExceptions inside the partially constructed ServiceManager.
   * This ISE wouldn't actually bubble up but would get logged by ExecutionQueue. This obfuscated
   * the original error (which was not constructing ServiceManager correctly).
   */
  public void testPartiallyConstructedManager() {

    assertThat(result).containsExactly(1, 15, 13, 8, 14);
  }

  /**
   * This tests a special case of the removeAt() call. Moving an element sideways on the heap could
   * 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(