CountingSupplier<TreeSet<Integer>> factory = new SortedSetSupplier();
    Map<Color, Collection<Integer>> map = Maps.newEnumMap(Color.class);
    SortedSetMultimap<Color, Integer> multimap = Multimaps.newSortedSetMultimap(map, factory);
    // newSortedSetMultimap calls the factory once to determine the comparator.
    assertEquals(1, factory.count);
    multimap.putAll(Color.BLUE, asList(3, 1, 4));
    assertEquals(2, factory.count);