assertThat(builder.build()).containsExactly("a", "b").inOrder();
    builder.add("c", "d");
    assertThat(builder.build()).containsExactly("a", "b", "c", "d").inOrder();
  }

  public void testBuilderWithDuplicateElements() {
    ImmutableSet<String> set =
        this.<String>builder()
            .add("a")
            .add("a", "a")
            .add("a", "a", "a")
            .add("a", "a", "a", "a")