set.add(new Derived("foo"));
    set.add(new Derived("bar"));
    assertThat(set).containsExactly(new Derived("bar"), new Derived("foo")).inOrder();
  }

  public void testNewTreeSetEmptyNonGeneric() {
    TreeSet<LegacyComparable> set = Sets.newTreeSet();
    assertTrue(set.isEmpty());
    set.add(new LegacyComparable("foo"));
    set.add(new LegacyComparable("bar"));
    assertThat(set)