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

    verifySetValue(target, B);
  }