### Question:
Labels extends ImmutableKeyValuePairs<String, String> { public Builder toBuilder() { Builder builder = new Builder(); builder.data.addAll(data()); return builder; }  abstract void forEach(LabelConsumer consumer); static Labels empty(); static Labels of(String key, String value); static Labels of(String key1, String value1, String key2, String value2); static Labels of(
      String key1, String value1, String key2, String value2, String key3, String value3); static Labels of(
      String key1,
      String value1,
      String key2,
      String value2,
      String key3,
      String value3,
      String key4,
      String value4); static Labels of(
      String key1,
      String value1,
      String key2,
      String value2,
      String key3,
      String value3,
      String key4,
      String value4,
      String key5,
      String value5); static Labels of(String[] keyValueLabelPairs); Builder toBuilder(); static Builder newBuilder();  }### Answer:
@Test void toBuilder() { Labels initial = Labels.of("one", "a"); Labels second = initial.toBuilder().setLabel("two", "b").build(); assertThat(initial.size()).isEqualTo(1); assertThat(second.size()).isEqualTo(2); assertThat(initial).isEqualTo(Labels.of("one", "a")); assertThat(second).isEqualTo(Labels.of("one", "a", "two", "b")); }