assertTrue(c.equals(of("a", "b", "c")));
    assertFalse(c.equals(of("a", "b", "d")));
  }

  abstract <E extends Comparable<E>> ImmutableSet.Builder<E> builder();

  public void testBuilderWithNonDuplicateElements() {
    ImmutableSet<String> set =
        this.<String>builder()
            .add("a")
            .add("b", "c")
            .add("d", "e", "f")
            .add("g", "h", "i", "j")