Java: Junit a class with Inject annotation

Question

@Singleton
public class RealWorkWindow implements WorkWindow {

    @Inject private Factory myFactory;

    public RealWorkWindow (
            LongSupplier longSupplier
    ) {
        defaultWindow = myFactory.create(() -> 1000L);
        workWindow = myFactory.create(longSupplier);
    } 
    ...

As you can see I am Injecting a factory class (injected via FactoryModuleBuilder)

Test code

@Test
public class RealWorkWindowTest {
    private RealWorkWindow testWindow;

    @BeforeMethod
    void setup() {
        MockitoAnnotations.initMocks(this);

        testWindow = spy(new RealWorkWindow(() -> 1L));
    }

Factory.py

public interface RealWorkWindowFactory {
    RealWorkWindowFactory create(LongSupplier longSupplier);
}

Module

install(new FactoryModuleBuilder()
                        .implement(WorkWindow.class, RealWorkWindow.class)
                        .build(RealWorkWindowFactory.class));

When I run the test RealWorkWindowTest the test fails with NPE that factory does not exists, which makes sense since I dont think injection runs.

How can I test with Injection in junit? or mock properly?

Similar to the problem describe in https://mhaligowski.github.io/blog/2014/05/30/mockito-with-both-constructor-and-field-injection.html

But the problem that I have is that mock is used IN constructor so it's still a null when instantiate the test object (because i have not called Mockito.init yet)

Answer 1

If you use a MockitoJUnitRunner, you can use @Mock to create a mock for the Factory and inject it.

@RunWith(MockitoJUnitRunner.class)
public class MyTest {

    @Mock
    private Factory myFactory;

    @InjectMocks
    private RealWorkWindow realWorkWindow;

    @Test
    public void testSomething() {
        when(myFactory.create(/* insert param here */)).thenReturn(/* insert return value here */);

        /* perform your test */
    }
}