assertEquals(1, (int) mmHeap.pollLast());
    assertThat(mmHeap.peek()).isNull();
    assertThat(mmHeap.peekLast()).isNull();
    assertThat(mmHeap.pollLast()).isNull();
  }

  public void testSmallMinHeap() {
    MinMaxPriorityQueue<Integer> mmHeap = MinMaxPriorityQueue.create();
    mmHeap.add(1);
    mmHeap.add(3);
    mmHeap.add(2);
    assertEquals(1, (int) mmHeap.peek());