Adding a Mock Object to a List-CodePudding

Currently I am trying create 10 mock objects of the same class for a test using Mockito in Java;

@Mock Bird bird1;

@Mock Bird bird2;

...

@Mock Bird bird10;

and I try to put these mock objects in a list since I will need to access them in a for loop to write their when-thenReturns and some other stuff like assigning all of these birds a name. However, when I try to do this it gives me a NullPointerException. It kind of makes sense that it gives that error, however I desperately try to find a way around for this and access these 10 mocks from some kind of a list or iterable. Is that possible?

Edit: Since @dawood-ibn-karem @pedro-luiz @tgdavies has asked for some more code, let me give it.

protected ArrayList<Bird> birds = new ArrayList<>();

  @Test
  public void testBirds() {
    // Arrange
    birdsListSetter();

    for (int i = 0; i < 10; i  ) {
      String voice= VoiceFixture.newRandomChirp();
      when(birds.get(i).getChirp()).thenReturn(voice);            
      }
    }
    // there some other stuff after this but the error occurs up here
  }

  public void birdsListSetter() {
    birds.add(bird1);
    birds.add(bird2);
    birds.add(bird3);
    birds.add(bird4);
    birds.add(bird5);
    birds.add(bird6);
    birds.add(bird7);
    birds.add(bird8);
    birds.add(bird9);
    birds.add(bird10);
  }

When I run the test, it fails at the first when-thenReturn saying that

NullPointerException: Cannot invoke "Bird.getChirp()" because the return value of "java.util.ArrayList.get(int)" is null

CodePudding user response：

I was basically thinking that adding @Mock was enough for initializing, but apparently I was wrong. Editing the code as

@Mock Bird bird1=mock(Bird.class)

fixed my problem. Thanks to kind helpers!

CodePudding user response：

Even though @saarantras answered that he solved his problem, I wanted to point it out that

@Mock Bird bird1=mock(Bird.class)

Is not the recommended usage @Mock and Mockito.mock().

@Mock

@Mock Bird bird1

Mockito.mock()

Bird bird1=mock(Bird.class)

Mockito.mock() method and @Mock annotation are doing slightly the same, which is defining a mock object in unit tests. However, there are some differences.

I'm not going into those differences, but you can have a look at

Mockito.mock() vs @Mock vs @MockBean

One thing that makes that NullPointerException happen is forgetting to add

@ExtendWith(MockitoExtension.class)
public class BirdTest {

@Mock Bird bird1;
@Mock Bird bird2;
@Mock Bird bird3;
@Mock Bird bird4;
@Mock Bird bird5;
@Mock Bird bird6;
@Mock Bird bird7;
@Mock Bird bird8;
@Mock Bird bird9;
@Mock Bird bird10;

At you test class level, wich isn't required when using Mockito.mock()