}

  private static final Comparator<Object> TO_STRING =
      new Comparator<Object>() {
        @Override
        public int compare(Object o1, Object o2) {
          return o1.toString().compareTo(o2.toString());
        }
      };

  public void testSupertypeComparator() {
    SortedSet<Integer> set =
        new ImmutableSortedSet.Builder<Integer>(TO_STRING).add(3, 12, 101, 44).build();