extends TestCase {
    abstract C createUnfiltered(Iterable<Integer> contents);

    abstract C filter(C elements, Predicate<? super Integer> predicate);

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