int getStrength(long previousDuration, long currentDuration, int strength) {
    if (isPreviousDurationCloserToGoal(previousDuration, currentDuration)) {
      return strength - 1;
    } else {
      return strength;
    }
  }
@Test
  void getStrengthShouldReturn4IfStrengthIs4() {
    // given
    int currentStrength = 4;

    // when
    int actual = bcCryptWorkFactorService.getStrength(0, 0, currentStrength);

    // then
    assertThat(actual).isEqualTo(4);
  }