NullPointerException.class,
        () ->
            Iterators.concat(
                iterateOver(1, 2), null, iterateOver(3), iterateOver(4), iterateOver(5)));
  }

  public void testConcatNested_appendToEnd() {
    int nestingDepth = 128;
    Iterator<Integer> iterator = iterateOver();
    for (int i = 0; i < nestingDepth; i++) {
      iterator = Iterators.concat(iterator, iterateOver(1));
    }

        NullPointerException.class,
        () ->
            Iterators.concat(
                iterateOver(1, 2), null, iterateOver(3), iterateOver(4), iterateOver(5)));
  }

  public void testConcatNested_appendToEnd() {
    int nestingDepth = 128;
    Iterator<Integer> iterator = iterateOver();
    for (int i = 0; i < nestingDepth; i++) {
      iterator = Iterators.concat(iterator, iterateOver(1));
    }