public static boolean equalContentsIgnoreOrder(Collection<?> c1, Collection<?> c2) {
        return c1.size() == c2.size() && c1.containsAll(c2);
    }
@Test
    public void testEqualContentsIgnoreOrder() {
        List<Integer> l2Copy = new ArrayList<>();
        l2Copy.addAll(l2);
        shuffle();
        assertTrue(CollectionUtil.equalContentsIgnoreOrder(l2, l2Copy));
        assertFalse(CollectionUtil.equalContentsIgnoreOrder(l1, l2));
    }