### Question:
MasterTableViewModel { public Integer getAge(){ if (contact.getBirthday() == null) { return null; } else { return (int) ChronoUnit.YEARS.between(contact.getBirthday(), LocalDate.now(CentralClock.getClock())); } } MasterTableViewModel(Contact contact); String getId(); String getFirstname(); String getLastname(); Integer getAge(); String getTitle(); String getEmailAddress(); String getCity(); String getStreet(); String getPostalCode();  }### Answer:
@Test public void testCalculationOfAge() { ZonedDateTime now = ZonedDateTime .of(LocalDate.of(2010, Month.JANUARY, 1), LocalTime.of(0, 0), ZoneId.systemDefault()); CentralClock.setFixedClock(now); Contact contact = new Contact(); contact.setBirthday(LocalDate.of(1987, Month.DECEMBER, 13)); MasterTableViewModel tableViewModel = new MasterTableViewModel(contact); assertThat(tableViewModel.getAge()).isEqualTo(22); }