*
   * <p>Results are undefined if {@code set1} and {@code set2} are sets based on different
   * equivalence relations, for example if {@code set1} is a {@link HashSet} and {@code set2} is a
   * {@link TreeSet} or the {@link Map#keySet} of an {@code IdentityHashMap}.
   */
  public static <E extends @Nullable Object> SetView<E> difference(Set<E> set1, Set<?> set2) {
    checkNotNull(set1, "set1");
    checkNotNull(set2, "set2");

    Set<Integer> set2 = newHashSet(2, 3);
    Set<Integer> difference = difference(set1, set2);
    assertThat(difference).containsExactly(1);
    set1.add(0);
    assertThat(difference).containsExactly(0, 1);
    set2.remove(2);
    assertThat(difference).containsExactly(0, 1, 2);
  }

  public void testSymmetricDifference_isView() {
    Set<Integer> set1 = newHashSet(1, 2);
    Set<Integer> set2 = newHashSet(2, 3);

    assertTrue(set.containsAll(Sets.newTreeSet(asList("a", "b", "f"))));
    assertFalse(set.containsAll(Sets.newTreeSet(asList("d"))));
    assertFalse(set.containsAll(Sets.newTreeSet(asList("z"))));
    assertFalse(set.containsAll(Sets.newTreeSet(asList("b", "d"))));
    assertFalse(set.containsAll(Sets.newTreeSet(asList("f", "d", "a"))));
  }

    BiPredicate<ImmutableSet<TypeWithDuplicates>, ImmutableSet<TypeWithDuplicates>> equivalence =
        (set1, set2) -> {
          if (!set1.equals(set2)) {
            return false;
          }
          for (int i = 0; i < set1.size(); i++) {
            if (!set1.asList().get(i).fullEquals(set2.asList().get(i))) {
              return false;
            }
          }
          return true;
        };

   *
   *   private static final class FooFactoryForTest {
   *     public static Foo create(String a, String b, int c, boolean d) {
   *       return Foo.builder()
   *           .setA(a)
   *           .setB(b)
   *           .setC(c)
   *           .setD(d)
   *           .build();
   *     }
   *   }
   *
   *   public void testEquals() {
   *     new ClassSanityTester()

   *
   *   private static final class FooFactoryForTest {
   *     public static Foo create(String a, String b, int c, boolean d) {
   *       return Foo.builder()
   *           .setA(a)
   *           .setB(b)
   *           .setC(c)
   *           .setD(d)
   *           .build();
   *     }
   *   }
   *
   *   public void testEquals() {
   *     new ClassSanityTester()

	// Retention configuration, needed to be passed along with lifecycle if set.
	Retention lock.Retention `msg:"-"`

	// Replication configuration
	Replication replicationConfig `msg:"-"`

	// StopDiskAtLimit will stop listing on each disk when limit number off objects has been returned.
	StopDiskAtLimit bool

	// pool and set of where the cache is located.
	pool, set int
}

func init() {
	gob.Register(listPathOptions{})

	for {
		select {
		case <-ctx.Done():
			return
		case <-timer.C:
			var wg sync.WaitGroup
			for _, set := range s.sets {
				wg.Add(1)
				go func(set *erasureObjects) {
					defer wg.Done()
					if set == nil {
						return
					}
					set.cleanupDeletedObjects(ctx)
				}(set)
			}
			wg.Wait()

			// Reset for the next interval
			timer.Reset(globalAPIConfig.getDeleteCleanupInterval())

        long seq1 = registration.getNextSequenceNumber();
        long seq2 = registration.getNextSequenceNumber();
        long seq3 = registration.getNextSequenceNumber();

        assertEquals(1, seq1);
        assertEquals(2, seq2);
        assertEquals(3, seq3);
        assertTrue(seq2 > seq1);
        assertTrue(seq3 > seq2);
    }

    @Test
    void testHeartbeatUpdate() throws InterruptedException {

	workerSize, err := env.GetInt(envRebalanceWorkers, len(pool.sets))
	if err != nil {
		rebalanceLogIf(ctx, fmt.Errorf("invalid workers value err: %v, defaulting to %d", err, len(pool.sets)))
		workerSize = len(pool.sets)
	}

	// Each decom worker needs one List() goroutine/worker
	// add that many extra workers.
	workerSize += len(pool.sets)

	wk, err := workers.New(workerSize)
	if err != nil {
		return err