assertEquals(3, (int) mmHeap.poll());
    assertThat(mmHeap.peekLast()).isNull();
    assertThat(mmHeap.peek()).isNull();
    assertThat(mmHeap.poll()).isNull();
  }

  public void testRemove() {
    MinMaxPriorityQueue<Integer> mmHeap = MinMaxPriorityQueue.create();
    mmHeap.addAll(Lists.newArrayList(1, 2, 3, 4, 47, 1, 5, 3, 0));
    assertTrue("Heap is not intact initially", mmHeap.isIntact());

    } else {
      assertThrows(UnsupportedOperationException.class, () -> map.putAll(mapToPut));
    }
    assertEquals(initialSize, map.size());
    assertInvariants(map);
  }

  public void testRemove() {
    Map<K, V> map;
    try {
      map = makePopulatedMap();
    } catch (UnsupportedOperationException e) {
      return;
    }
    K keyToRemove = map.keySet().iterator().next();