public void testImmutableCopy_empty() {
    assertThat(union(emptySet(), emptySet()).immutableCopy()).isEmpty();
    assertThat(intersection(newHashSet(1, 2), newHashSet(3, 4)).immutableCopy()).isEmpty();
    assertThat(difference(newHashSet(1, 2), newHashSet(1, 2)).immutableCopy()).isEmpty();
    assertThat(symmetricDifference(newHashSet(1, 2), newHashSet(1, 2)).immutableCopy()).isEmpty();
  }

  public void testImmutableCopy() {

                  : new MutatedOnQueryList<>(
                      transform(infiniteSetsFromStartIndex, ImmutableList::copyOf));
          Set<String> immutableCopy;
          try {
            immutableCopy = copyOf(input);
          } catch (RuntimeException e) {
            throw new RuntimeException(
                Strings.lenientFormat(

   * stable. There is usually no reason to retain a reference of type {@code SetView}; typically,
   * you either use it as a plain {@link Set}, or immediately invoke {@link #immutableCopy} or
   * {@link #copyInto} and forget the {@code SetView} itself.
   *
   * @since 2.0
   */
  public abstract static class SetView<E extends @Nullable Object> extends AbstractSet<E> {