@Test
  public void testCompareNullSdKey() {
    assertThat(MetaStoreServerUtils.StorageDescriptorKey.UNSET_KEY,
        is(new MetaStoreServerUtils.StorageDescriptorKey()));
  }
Two empty StorageDescriptorKey should be equal.
standalone-metastore/metastore-server/src/test/java/org/apache/hadoop/hive/metastore/utils/TestMetaStoreServerUtils.java