assertThat(Optional.presentInstances(optionals)).containsExactly("a", "c").inOrder();
  }

  @SuppressWarnings("DuplicateAssertion") // We intentionally iterate multiple times.
  public void testPresentInstances_callingIteratorTwice() {
    List<Optional<String>> optionals =
        ImmutableList.of(Optional.of("a"), Optional.<String>absent(), Optional.of("c"));
    Iterable<String> onlyPresent = Optional.presentInstances(optionals);