@Override
  protected SortedMap<String, String> makeEmptyMap() {
    return transformValues(Maps.<String, String>newTreeMap(), Functions.<String>identity());
  }

  @Override
  protected SortedMap<String, String> makePopulatedMap() {
    SortedMap<String, Integer> underlying = Maps.newTreeMap();
    underlying.put("a", 1);
    underlying.put("b", 2);
    underlying.put("c", 3);

  public void testSameComparator() {
    assertTrue(SortedIterables.hasSameComparator(Ordering.natural(), Sets.newTreeSet()));
    assertTrue(SortedIterables.hasSameComparator(Ordering.natural(), Maps.newTreeMap().keySet()));
    assertTrue(
        SortedIterables.hasSameComparator(
            Ordering.natural().reverse(), Sets.newTreeSet(Ordering.natural().reverse())));
  }

  public void testComparator() {

    Supplier<TreeMap<Integer, Character>> factory =
        new Supplier<TreeMap<Integer, Character>>() {
          @Override
          public TreeMap<Integer, Character> get() {
            return Maps.newTreeMap();
          }
        };
    Map<String, Map<Integer, Character>> backingMap = new LinkedHashMap<>();
    Table<String, Integer, Character> table = newCustomTable(backingMap, factory);
    populate(table, data);