protected Iterator<Integer> newTargetIterator() {
        return Iterators.concat(iterateOver(1));
      }
    }.test();
  }

  @GwtIncompatible // slow (~5s)
  public void testConcatEmptyAndSingletonAndEmptyYieldsSingleton() {
    new SingletonIteratorTester() {
      @Override
      protected Iterator<Integer> newTargetIterator() {
        return Iterators.concat(iterateOver(), iterateOver(1), iterateOver());
      }