});

    assertThrows(NullPointerException.class, () -> powerSet(singleton(null)));
  }

  public void testPowerSetEqualsAndHashCode_verifyAgainstHashSet() {
    ImmutableList<Integer> allElements =
        ImmutableList.of(
            4233352, 3284593, 3794208, 3849533, 4013967, 2902658, 1886275, 2131109, 985872,
            1843868);