public RatingValue increment(Rating rating) {
    if (value.compareTo(rating) > 0) {
      value = rating;
    }
    this.set = true;
    return this;
  }
@Test
  public void multiple_calls_to_increment_increments_by_the_value_of_the_arg() {
    RatingValue target = new RatingValue()
      .increment(new RatingValue().increment(B))
      .increment(new RatingValue().increment(D));

    verifySetValue(target, D);
  }