@Test
public void bothEmpty() throws Exception {

    MergerBiFunction<Integer> merger = new MergerBiFunction<Integer>(new Comparator<Integer>() {
        @Override
        public int compare(Integer o1, Integer o2) {
            return o1.compareTo(o2);
        }
    });
    List<Integer> list = merger.apply(Collections.<Integer>emptyList(), Collections.<Integer>emptyList());
    assertEquals(Collections.<Integer>emptyList(), list);
}