assertEquals(unfiltered.pollLast(), filtered.pollLast());
        assertEquals(unfiltered, filtered);
      }
    }

    public void testNavigation() {
      for (List<Integer> contents : SAMPLE_INPUTS) {
        NavigableSet<Integer> filtered = filter(createUnfiltered(contents), EVEN);
        NavigableSet<Integer> unfiltered = createUnfiltered(filtered);