@Override
  public int size() {
    return partitionMaps.values().stream().mapToInt(Map::size).sum();
  }
@Test
  public void testSize() {
    PartitionMap<String> map = PartitionMap.create(SPECS);
    map.put(UNPARTITIONED_SPEC.specId(), null, "v1");
    map.put(BY_DATA_SPEC.specId(), Row.of("aaa"), "v2");
    map.put(BY_DATA_SPEC.specId(), Row.of("bbb"), "v3");
    map.put(BY_DATA_CATEGORY_BUCKET_SPEC.specId(), Row.of("ccc", 2), "v4");
    assertThat(map).isNotEmpty();
    assertThat(map).hasSize(4);
  }