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

WarSame :

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.

DevMike01 :

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);
    }