return Iterators.concat(iterateOver(1), iterateOver(), iterateOver(), iterateOver(2));
      }
    }.test();
  }

  @GwtIncompatible // fairly slow (~50s)
  public void testConcatUnmodifiable() {
    new IteratorTester<Integer>(
        5, UNMODIFIABLE, asList(1, 2), IteratorTester.KnownOrder.KNOWN_ORDER) {
      @Override
      protected Iterator<Integer> newTargetIterator() {

        return Iterators.concat(iterateOver(1), iterateOver(), iterateOver(), iterateOver(2));
      }
    }.test();
  }

  @GwtIncompatible // fairly slow (~50s)
  public void testConcatUnmodifiable() {
    new IteratorTester<Integer>(
        5, UNMODIFIABLE, asList(1, 2), IteratorTester.KnownOrder.KNOWN_ORDER) {
      @Override
      protected Iterator<Integer> newTargetIterator() {