@Test
public void filter() {

  Object object1 = new Object();
  Object object2 = new Object();
  Object object3 = new Object();
  List<Object> list1 = new ArrayList<Object>();
  list1.add(object1);
  list1.add(object2);
  List<Object> list2 = new ArrayList<Object>();
  list2.add(object2);
  list2.add(object3);
  doReturn(list1).doReturn(list2).when(filter).filter(anyList());
  List<Object> actualObjects = diffFilter.filter(list1);
  assertEquals(object1, actualObjects.get(0));
}