}

  public void testMapWithIndex_linkedHashSetSource() {
    testMapWithIndex(elems -> new LinkedHashSet<>(elems).stream());
  }

  public void testMapWithIndex_unsizedSource() {
    testMapWithIndex(
        elems ->
            Stream.<@Nullable Object>of((Object) null)
                .flatMap(unused -> ImmutableList.copyOf(elems).stream()));
  }