Mockito - NullpointerException when stubbing Metho

Question

So I started writing tests for our Java-Spring-project.

What I use is JUnit and Mockito. It's said, that when I use the when()...thenReturn() option I can mock services, without simulating them or so. So what I want to do is, to set:

when(classIwantToTest.object.get().methodWhichReturnsAList(input))thenReturn(ListcreatedInsideTheTestClass)  

But no matter which when-clause I do, I always get a NullpointerException, which of course makes sense, because input is null.

Also when I try to mock another method from an object:

when(object.method()).thenReturn(true)

There I also get a Nullpointer, because the method needs a variable, which isn't set.

But I want to use when()..thenReturn() to get around creating this variable and so on. I just want to make sure, that if any class calls this method, then no matter what, just return true or the list above.

Is it a basically misunderstanding from my side, or is there something else wrong?

Code:

public class classIWantToTest implements classIWantToTestFacade{
        @Autowired
        private SomeService myService;

        @Override
        public Optional<OutputData> getInformations(final InputData inputData) {
            final Optional<OutputData> data = myService.getListWithData(inputData);
            if (data.isPresent()) {
                final List<ItemData> allData = data.get().getItemDatas();
                    //do something with the data and allData
                return data;
            }

            return Optional.absent();
        }   
}

And here is my test class:

public class Test {

    private InputData inputdata;

    private ClassUnderTest classUnderTest;

    final List<ItemData> allData = new ArrayList<ItemData>();

    @Mock
    private DeliveryItemData item1;

    @Mock
    private DeliveryItemData item2;



    @Mock
    private SomeService myService;


    @Before
    public void setUp() throws Exception {
        classUnderTest = new ClassUnderTest();
        myService = mock(myService.class); 
        classUnderTest.setService(myService);
        item1 = mock(DeliveryItemData.class);
        item2 = mock(DeliveryItemData.class);

    }


    @Test
    public void test_sort() {
        createData();
        when(myService.getListWithData(inputdata).get().getItemDatas());

        when(item1.hasSomething()).thenReturn(true);
        when(item2.hasSomething()).thenReturn(false);

    }

    public void createData() {
        item1.setSomeValue("val");
        item2.setSomeOtherValue("test");

        item2.setSomeValue("val");
        item2.setSomeOtherValue("value");

        allData.add(item1);
        allData.add(item2);


}

Answer 1

For future readers, another cause for NPE when using mocks is forgetting to initialize the mocks like so:

@Mock
SomeMock someMock;

@InjectMocks
SomeService someService;

@Before
public void setup(){
    MockitoAnnotations.initMocks(this); //without this you will get NPE
}

@Test
public void someTest(){
    Mockito.when(someMock.someMethod()).thenReturn("some result");
   // ...
}

Answer 2

faced the same issue, the solution that worked for me:

Instead of mocking the service interface, I used @InjectMocks to mock the service implementation:

@InjectMocks
private exampleServiceImpl exampleServiceMock;

instead of :

@Mock
private exampleService exampleServiceMock;

Answer 3

I had this issue and my problem was that I was calling my method with any() instead of anyInt(). So I had:

doAnswer(...).with(myMockObject).thisFuncTakesAnInt(any())

and I had to change it to:

doAnswer(...).with(myMockObject).thisFuncTakesAnInt(anyInt())

I have no idea why that produced a NullPointerException. Maybe this will help the next poor soul.

Answer 4

I had the same problem and my issue was simply that I had not annotated the class properly using @RunWith. In your example, make sure that you have:

@RunWith(MockitoJUnitRunner.class)
public class Test {
...

Once I did that, the NullPointerExceptions disappeared.

Answer 5

In my case, I missed add first

PowerMockito.spy(ClassWhichNeedToBeStaticMocked.class);

so this can be helpful to somebody who see such error

java.lang.NullPointerException
    at org.powermock.api.mockito.internal.expectation.PowerMockitoStubberImpl.addAnswersForStubbing(PowerMockitoStubberImpl.java:67)
    at org.powermock.api.mockito.internal.expectation.PowerMockitoStubberImpl.when(PowerMockitoStubberImpl.java:42)
    at org.powermock.api.mockito.internal.expectation.PowerMockitoStubberImpl.when(PowerMockitoStubberImpl.java:112)