.addEqualityGroup("notASet")
          .testEquals();
      assertEquals(toHashSets(powerSet1).hashCode(), powerSet1.hashCode());
    }
  }

  public void testPowerSetEquals_independentOfOrder() {
    ImmutableSet<Integer> elements = ImmutableSet.of(1, 2, 3, 4);
    Set<Set<Integer>> forward = powerSet(elements);
    Set<Set<Integer>> reverse = powerSet(ImmutableSet.copyOf(elements.asList().reverse()));