public Iterator<Integer> iterator() {
            return newDoubler(2, 32);
          }
        };
    assertThat(doubled).containsExactly(2, 4, 8, 16, 32).inOrder();
  }

  public void testSampleCode() {
    Iterable<Integer> actual =
        new Iterable<Integer>() {
          @Override
          public Iterator<Integer> iterator() {
            Iterator<Integer> powersOfTwo =