Mockito - mock builder returns a null object even when returns_self is used

Question

I have created a test for Notifications in Android and am struggling with making Mock objects. When I try to Mock the notificationBuilder following this post(which suggests wrapping Android notifications in a custom class) I get a null notificationBuilder , which then ruins my tests.

My minimal code showing this is:

@Before
public void setUp() {
    NotificationCompat.Builder notificationBuilder = Mockito.mock(NotificationCompat.Builder.class, Mockito.RETURNS_SELF);
}

where notificationBuilder is null. How can I get a Mock NotificationCompat.Builder as the return value? I thought this was what RETURNS_SELF was supposed to do.

With a null value I can't use my Builder as part of a when().then() for further testing.

Answer 1

The problem is that you are creating a mock which in the end is a local variable inside the @Before method.

When you later run your tests this variable is not accessible anymore, nor there is any notion of a global mock for a class (at least in vanilla Mockito).

So either use a global variable which you then initialize manually in the setUp method:

private NotificationCompat.Builder notificationBuilder;

@Before
public void setUp() {
   notificationBuilder = Mockito.mock(NotificationCompat.Builder.class);
}

or use Mockito annotations:

@Mock
private NotificationCompat.Builder notificationBuilder;

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

Answer 2

The Mockito.mock(...) is returning null because you aren't mocking anything. You need to declare a global variable with the @Mock annotation and initialize your mock object in the setUp() method(you can call this anything as long as it has the @Before annotation on it). Try the below code snippet.

    @Mock
    NotificationCompat.Builder notificationBuilder;

    @Before
    public void setUp(){
        notificationBuilder = Mockito.mock(NotificationCompat.Builder
                .class);

    }
   @Test
    public void testSharedPrefInjection(){

        assertNotNull(notificationBuilder);
    }