[FIXED] How to write unit test for void delete method using junit and mockito?

Issue

public void delete(Long id){
Optional<Car> optional = CarRepository.findById(id);
if(optional.isPresent()){
    Car car = optional.get();
    car.setActionStatus("DELETE");
    CarRepository.save(car);
}
else{
    throw new CustomException("custom message");
}}

I have to write a unit test for the above delete method, here we are not deleting the record instead we are just updating the setActionStatus to delete.

Solution

First, don't use static methods on your CarRepository, make an interface:

interface CarRepository {
  Car findById(long id);
  void save(Car car);
  ...
}

and pass an instance of this to the class you want to test:

class ClassToTest {
  public ClassToTest(CarRepository carRepository) { ... }
  ...
}

now in your test you can use a mock CarRepository:

...
@Test
void test() {
  // create the mocks we need and set up their behaviour
  CarRepository carRepository = mock(CarRepository.class);
  Car car = mock(Car.class);
  when(carRepository.findById(123)).thenReturn(car);

  // create the instance we will test and give it our mock
  ClassToTest classToTest = new ClassToTest(carRepository);
  classToTest.delete(123);

  // check that the expected methods were called
  verify(car).setActionStatus("DELETE");
  verify(carRepository).save(car);
}

Answered By - tgdavies
Answer Checked By - Timothy Miller (JavaFixing Admin)