Ignoring not void method inside testing method in Mockito

Question

In class Account I have a method public Account reserveA() which I want to test, inside reserveA is called a method public Bank DAO.createB(). Is there a way to call reserveA() in test method but ignore call DAO.createB()? Non of these methods are void. I tried:

doNothing().when(Account).reserveA(param1, param2);

but it's not the proper way.

Answer 1

doNothing() is reserved only for void methods. If your method returns something, then you are required to do as well (or throw exception). Depending on complexity of your Account.reserveString(), you may need to mock some more than just this one method call if result is used somewhere else.

Trying to use doNothing() on non-void method results in error:

org.mockito.exceptions.base.MockitoException: 
Only void methods can doNothing()!
Example of correct use of doNothing():
    doNothing().
    doThrow(new RuntimeException())
    .when(mock).someVoidMethod();
Above means:
someVoidMethod() does nothing the 1st time but throws an exception the 2nd time is called

Consider such classes:

@Component
public class BankDao {
    public BankDao() {}

    public void createVoid() {
        System.out.println("sth - 1");
    }

    public String createString(){
        return "sth - 2";
    }
}

@Service
public class Account {
    @Autowired
    private final BankDao DAO;

    public Account(BankDao dao) {
        this.DAO = dao;
    }
    public void reserveVoid() {
        System.out.println("before");
        DAO.createVoid();
        System.out.println("after");
    }
    public void reserveString() {
        System.out.println(DAO.createString());
    }
}

For which Test class is made:

@RunWith(MockitoJUnitRunner.class)
public class AccountTest {
    @Mock
    private BankDao bankDao;

    @InjectMocks
    private Account account;

    @Test
    public void reserveVoid_mockBankDaoAndDontUseRealMethod() {
        doNothing().when(bankDao).createVoid();
        account.reserveVoid();
    }

    @Test
    public void reserveString_mockBankDaoAndDontUseRealMethod() {
        when(bankDao.createString()).thenReturn("nothing");
        account.reserveString();
    }
}

Running such a test will produce:

nothing
before
after

If you change @Mock to @Spy and remove lines with doNothing() and when(), then you'll be calling original methods. Result would be:

sth - 2
before
sth - 1
after