assertTrue("Iterator has reached end prematurely", it.hasNext());
    it.next();
    it.next();
    assertThrows(NoSuchElementException.class, () -> it.next());
  }

  public void testIteratorConcurrentModification() {
    MinMaxPriorityQueue<Integer> mmHeap = MinMaxPriorityQueue.create();
    mmHeap.addAll(Lists.newArrayList(1, 2, 3, 4));
    Iterator<Integer> it = mmHeap.iterator();