@Override
  public Collection<V> values() {
    List<V> values = Lists.newArrayList();

    for (Map<StructLike, V> partitionMap : partitionMaps.values()) {
      values.addAll(partitionMap.values());
    }

    return Collections.unmodifiableCollection(values);
  }
@Test
  public void testValues() {
    PartitionMap<Integer> map = PartitionMap.create(SPECS);
    map.put(BY_DATA_SPEC.specId(), Row.of("aaa"), 1);
    map.put(BY_DATA_CATEGORY_BUCKET_SPEC.specId(), Row.of("aaa", 2), 2);
    map.put(BY_DATA_SPEC.specId(), Row.of("bbb"), 3);
    assertThat(map.values()).containsAll(ImmutableList.of(1, 2, 3));
  }