void () { List<Integer> a1 = new ArrayList<>(Arrays.asList(0, 1)); List<Integer> l = ContainerUtil.concat(a1, Arrays.asList(2, 3), ContainerUtil.emptyList()); assertEquals(4, l.size()); for (int i = 0; i < l.size(); i++) { int at = l.get(i); assertEquals(i, at); } try { a1.clear(); l.get(3); fail(); } catch (ConcurrentModificationException ignore) { } }