Injecting beans in a JUnit/Mockito test returns zero

I have a JavaEE application with Stateless EJBs that I use for business logic (EjbBusiness) and database access (EjbDAO). I need to run a unit test on EjbBusiness, but the DAO method always returns zero.

In the example below I have both classes and the unit test. I mock the EjbDAO method that connects to the database, to return a testing SQL connection:

@Stateless
public class EjbDAO {
	
	
	public Connection getConnFromPool() {
		Connection conn = null; // in production this would return a connection
		return conn;
	}
	
	
	public int add2(int i) {
		Connection conn = getConnFromPool();
        System.out.println("in EjbDAO: " + i);
		return i + 2;
	}

}


@Stateless
public class EjbBusiness {

	
	@Inject
	private EjbDAO dao;
	
	
	public int add2(int i) {
		 int j = dao.add2(i);
         System.out.println("in EjbBusiness: " + j);
		 return j;
            
	}
	
}

Since I mock one of the methods of EjbDAO, I annotate it with @Spy in UnitTest:

@RunWith(MockitoJUnitRunner.class)
public class UnitTest {

	@InjectMocks
	private EjbBusiness biz;
	
	@InjectMocks
	@Spy
	private EjbDAO dao;
	
	@Before
	public void setup() {
		dao = Mockito.mock(EjbDAO.class);
		biz = Mockito.mock(EjbBusiness.class);
	    MockitoAnnotations.initMocks(this);
	}
	
	
	@Test
	public void testBean() {
		
        // this would return the testing connection
		Mockito.doReturn(null).when(dao).getConnFromPool();

		int i = biz.add2(3);

		assertThat(5).isEqualTo(i);
	}
}

Problem is that the assertion doesn't work, as biz.add2(3) returns zero instead of 5. Also, the System.out.println in both beans is not printed. How to declare/mock the beans for the test to work?

Use @InjectMocks only when you calling actual method otherwise don't use it. And also don't use @InjectMocks and Mockito.mock() or @Mock together.

In your code you are using @InjectMocks on dao object and you are also creatign mock for that. And use Mockito.mock() when you want to stub the method calls instead of calling actual methods.

System.out.println() is not working in your code because you created mocks for objects biz and dao. Actual methods (i.e add2() because of this you are getting 0 as output) not executed when you call with mock objects.

For more info on when to use @InjectMocks refer
this

@RunWith(MockitoJUnitRunner.class)
public class UnitTest {

	@InjectMocks
    private EjbBusiness biz;

	@Mock
    private EjbDAO dao;

    @Before
    public void setup() {
        MockitoAnnotations.initMocks(this);
    }


    @Test
    public void testBean() {

        // this would return the testing connection
    	Mockito.doReturn(null).when(dao).getConnFromPool();
    	Mockito.doCallRealMethod().when(dao).add2(Mockito.anyInt());

        int i = biz.add2(3);

        assertThat(i).isEqualTo(5);
    }
}

You should not use one unit test to test both classes.
You should have two test classes to test them.

For Example,

@RunWith(MockitoJUnitRunner.class)
public class EjbBusinessTest {

    @InjectMocks
    private EjbBusiness biz;

    @Mock
    private EjbDAO dao;


    @Test
    public void testAdd2() {

        // this would return the testing connection
        Mockito.doReturn(null).when(dao).getConnFromPool();
        Mockito.doReturn(5).when(dao).add2();

        int i = biz.add2(3);

        assertThat(5).isEqualTo(i);
    }
}

In the above class we are testing only the method EjbBusinessTest.add2 and we don't care what happens or if the method EjbDAO.add2 is working properly. In this all we should care is whether the method under test is working properly, hence we mock everything external to that method.

Following a similar approach for EjbDAO.add2 as well, The test case should look like something given below. I have also made the method EjbDAO.getConnection private so that that should also be included in the test. This choice should be made by you if you need to make it private or public. If you decide to keep it public then you should use @Spy on EjbDAO and mock the EjbDAO.getConnection method.

@RunWith(MockitoJUnitRunner.class)
public class EjbDAOTest {

    //instantiate this object the way you want. Mock the external objects used inside this like the library used to get connection inside EjbDAO.getConnection() Method  
    @InjectMocks
    private EjbDAO dao;


    @Test
    public void testAdd2() {

        // I would suggest you to make the getConnection method private.
        // do not mock the getConnection here, instead mock how you are getting the connection inside the  getConnection method. 
        int i = dao.add2(3);

        assertThat(5).isEqualTo(i);
    }
}

Hope it helps.