Is it possible to invoke mocked object's method in constructor?

Question

I have, for example, these classes with Spring Boot. I try to do a REST API without a database and wieh files as data. The data files are like this:

{ "persons": [ { "firstName":"John", "lastName":"Boyd", "address":"1509 Culver St", "city":"Culver", "zip":"97451", "phone":"841-874-6512", "email":"jaboyd@email.com" }, { "firstName":"Jacob", "lastName":"Boyd", "address":"1509 Culver St", "city":"Culver", "zip":"97451", "phone":"841-874-6513", "email":"drk@email.com" } ] }

@Repository
public class PersonRepository {

    private List<Person> persons;
    private DataLoaderService loaderService;
  
    @Autowired
    public PersonRepository(DataLoaderService loaderService){
        persons = loaderService.convertJsonToPojo("Persons",Person.class);
    }
    
    public List<Person> getAll(){
        return persons;
    }

}

@Service
public class DataLoaderService {

    private JsonFileService jsonFileService;
    private ObjectMapper mapper

    @Autowired
    public DataLoaderService(JsonFileService jsonFileService,ObjectMapper mapper){
        this.jsonFileService = jsonFileService;
        this.mapper = mapper;
    }

    public <T> List<T> convertJsonToPojo(String nodeName, Class <T> classOfT){
         
    }

}

So, I have a file. How can I read to transform to a list of Pojo?

When I want to mock the test method getAll(), my list size is 0. The mock doesn't give me values because I think the problem is that I initialized the value in the constructor. Here is my test:

@ExtendWith(MockitoExtension.class)
public class PersonRepositoryTest {
    
    PersonRepository repository;
    
    @Mock
    private DataLoaderService loaderService;
    
    @BeforeEach
    public void setUp() {
        repository = new PersonRepository(loaderService);
    }

    @Test
    public void getAllPersonnesInConstructor() {
        List<Person> mockedList = Arrays.asList(                
                new Person("Paul","Moes","1", "7777", "adresse tour", "Chicago", "pauln@gmail.com"),
                new Person("Eleson","Moc","2", "77777", "ddkdkd", "New York", "eleson@gmail.com")
                );
        doReturn(mockedList).when(loaderService).convertJsonToPojo("persons",Person.class);
        
        List<Person> persons = repository.getAll();

        assertEquals(2,persons.size(),"Expected list size is 2");
        assertEquals(persons,mockedList);
    }

}

If i use @Spy, I have an error.

When I use method getAll() without initializing the variable persons in the constructor but in the method getAll, it is OK, like this:

public List<Person> getAll() {
        this.persons = this.dataLoaderService.convertJsonToPojo("persons", Person.class);
        log.debug("persons getALL repository" + persons);
        return this.persons;
}

What can I do to test it?

Test a method which initializes a value in the constructor.

score 0 · Answer 1 · answered Feb 28 '23 at 20:56

You have two mistakes in your test:

You mock convertJsonToPojo("persons", Person.class), whereas PersonRepository does convertJsonToPojo("Persons", Person.class). Note "persons" vs. "Persons".
When PersonRepository invokes the convertJsonToPojo method on your mock, you didn't stub (doReturn etc.) anything so far. This is why you get the default answer, i.e., a list of size 0.

To make it work, modify your test as follows:

@ExtendWith(MockitoExtension.class)
class PersonRepositoryTest {

    PersonRepository classUnderTest;

    @Mock
    DataLoaderService dataLoaderServiceMock;

    @Test
    void getAllPersonnesInConstructor() {
        List<Person> pojos = List.of(
                new Person("Paul", "Moes", "1", "7777", "adresse tour", "Chicago", "pauln@gmail.com"),
                new Person("Eleson", "Moc", "2", "77777", "ddkdkd", "New York", "eleson@gmail.com")
        );
        when(dataLoaderServiceMock.convertJsonToPojo("Persons", Person.class)).thenReturn(pojos);
        classUnderTest = new PersonRepository(dataLoaderServiceMock);

        List<Person> persons = classUnderTest.getAll();

        assertEquals(persons, persons);
    }

}

Now stubbing happens before the actual invocation of convertJsonToPojo.

Side notes:

There is no need for doReturn, you can use when. See also: https://stackoverflow.com/a/20360269/3429133
There is also no need for two assertEquals. Checking for equality of the list includes the list's size.

Is it possible to invoke mocked object's method in constructor?

1 Answers1