public WorkDuration multiply(int factor) {
    return WorkDuration.createFromMinutes(this.toMinutes() * factor, this.hoursInDay);
  }
@Test
  public void multiply() {
    // 5h * 2 = 1d 2h
    WorkDuration result = WorkDuration.createFromValueAndUnit(5, WorkDuration.UNIT.HOURS, HOURS_IN_DAY).multiply(2);
    assertThat(result.days()).isOne();
    assertThat(result.hours()).isEqualTo(2);
    assertThat(result.minutes()).isZero();
    assertThat(result.hoursInDay()).isEqualTo(HOURS_IN_DAY);
  }