new EqualsTester()
            .addEqualityGroup(expected, filter(createUnfiltered(contents), EVEN))
            .testEquals();
      }
    }
  }

  public abstract static class AbstractFilteredSortedSetTest<C extends SortedSet<Integer>>
      extends AbstractFilteredSetTest<C> {
    public void testFirst() {
      for (List<Integer> contents : SAMPLE_INPUTS) {