public void testAddMutator() {
    setUpTest();
    c.setMutator(
        new CompositeCollection.CollectionMutator() {
          public boolean add(CompositeCollection composite, Collection[] collections, Object obj) {
            for (int i = 0; i < collections.length; i++) {
              collections[i].add(obj);
            }
            return true;
          }

          public boolean addAll(
              CompositeCollection composite, Collection[] collections, Collection coll) {
            for (int i = 0; i < collections.length; i++) {
              collections[i].addAll(coll);
            }
            return true;
          }

          public boolean remove(
              CompositeCollection composite, Collection[] collections, Object obj) {
            return false;
          }
        });

    c.addComposited(one);
    c.add("foo");
    assertTrue(c.contains("foo"));
    assertTrue(one.contains("foo"));
  }