SortedSet<Integer> set =
        new ImmutableSortedSet.Builder<Integer>(TO_STRING).add(3, 12, 101, 44).build();
    assertThat(set).containsExactly(101, 12, 3, 44).inOrder();
  }

  public void testSupertypeComparatorSubtypeElements() {
    SortedSet<Number> set =
        new ImmutableSortedSet.Builder<Number>(TO_STRING).add(3, 12, 101, 44).build();
    assertThat(set).containsExactly(101, 12, 3, 44).inOrder();
  }

  @Override