} else {
      assertThat(map.isEmpty()).isTrue();
    }
    assertCollectionSize(map.keySet(), size);
    assertCollectionSize(map.entrySet(), size);
    assertCollectionSize(map.values(), size);
  }

  @SuppressWarnings("IterablesSizeOfCollection") // we are testing our iterator implementation
  private void assertCollectionSize(Collection<?> collection, int size) {
    assertThat(collection.size()).isEqualTo(size);