Mockito always returns null as a result of calling an EJB

Question

I'm trying to call the second method of this class, and always get null . Note that it returns new User() however in the test class I always get null :

@Stateless
public class UserDAO2 {

    public Connection getConnFromPool(int i) {
        return null;
    }

    public User readByUserid(String s) {
        System.out.println("In DAO 2");
        Connection c = getConnFromPool(1);
        return new User();
    }
}

And the test class:

@RunWith(MockitoJUnitRunner.class)
public class UserBeanUnitTest {

    @InjectMocks
    private UserDAO2 dao2;

    @Before
    public void setup() {
        dao2 = Mockito.mock(UserDAO2.class);
        MockitoAnnotations.initMocks(this);
    }


    @Test
    public void testBean() {

        Mockito.when(dao2.getConnFromPool(1)).thenReturn(null);

        User expectedUser = new User();
        expectedUser.setSk(1);
        expectedUser.setFirstName("David");
        expectedUser.setLastName("Gahan");
        expectedUser.setUserid("user1");

        User user = dao2.readByUserid("user1"); // <-- this method always returns null

        assertThat(user).isEqualTo(expectedUser); // <-- test fails as expectedUser != null

    }

}

Also, note that System.out.println is never printed. How to fix this to actually make a call to dao.readByUserid() ?

Answer 1

If you need to test the method of some class, and inside of it the other method of the same class is called which you want to mock, then you need to use @Spy :

@RunWith(MockitoJUnitRunner.class)
public class UserDAO2Test {

    @InjectMocks
    @Spy
    private UserDAO2 dao;

    @Test
    public void testBean() {

        Mockito.doReturn(null).when(dao).getConnFromPool(1);

        User expectedUser = new User();
        expectedUser.setSk(1);
        expectedUser.setFirstName("David");
        expectedUser.setLastName("Gahan");
        expectedUser.setUserid("user1");

        User user = dao.readByUserid("user1");

        assertThat(user).isEqualTo(expectedUser);
    }
}

Note that I slightly modified the line with mocking getConnFromPool because it's required when you use that technique.

See docs for spying.