@Override
  public void clear() {
    partitionMaps.clear();
  }
@Test
  public void testClear() {
    PartitionMap<String> map = PartitionMap.create(SPECS);
    map.put(UNPARTITIONED_SPEC.specId(), null, "v1");
    map.put(BY_DATA_SPEC.specId(), Row.of("aaa"), "v2");
    assertThat(map).hasSize(2);
    map.clear();
    assertThat(map).isEmpty();
  }