}

  public void testPowerSetIteration_manual() {
    ImmutableSet<Integer> elements = ImmutableSet.of(1, 2, 3);
    Set<Set<Integer>> powerSet = powerSet(elements);
    // The API doesn't promise this iteration order, but it's convenient here.
    Iterator<Set<Integer>> i = powerSet.iterator();
    assertEquals(ImmutableSet.of(), i.next());
    assertEquals(ImmutableSet.of(1), i.next());