assertFalse(permutationSet.contains(newArrayList(1, 1, 2, 3)));
    assertFalse(permutationSet.contains(newArrayList(1, 2, 3, 4)));
    assertFalse(permutationSet.contains(null));
  }

  public void testPermutationSetEmpty() {
    Collection<List<Integer>> permutationSet =
        Collections2.permutations(Collections.<Integer>emptyList());

    assertEquals(1, permutationSet.size());