*
   * <p>TODO(kevinb): move to the test class?
   */
  @VisibleForTesting
  boolean isIntact() {
    for (int i = 1; i < size; i++) {
      if (!heapForIndex(i).verifyIndex(i)) {
        return false;
      }
    }
    return true;
  }

  /**
   * Each instance of MinMaxPriorityQueue encapsulates two instances of Heap: a min-heap and a