assertThat(filtered.descendingSet())
            .containsExactlyElementsIn(unfiltered.descendingSet())
            .inOrder();
      }
    }

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