Mockito is unable to create instance using @InjectMocks because of Static class in constructor

Question

I have to unit test in some code(Not written by me), but I am stuck at one place. I am using Powermock and mockito. So the issue is @InjectMocks call default constructor before even testing a method, inside the default constructor, they have used a static class and a setter to set a field, and hence injecting mocks using @Inject is unable to create the instance. Is there any way to fix this with changing the API code?

    RunWith(PowerMockRunner.class)
    @PrepareForTest(UserGroup.class)
    public class SomeServiceImplTest {

    @Mock
    private SomeDAOImpl SomeDAOImpl;


    @Mock
    private UserGroup userGroup;


    @InjectMocks
    SomeServiceImpl someServiceImpl;


    @Test
    public void testSomeMethod(){
         String username = "UserToBeTest";
     //Some code

     //     
         verify(SomeDAOImpl).saveUserGroup(any(),any());
     }
}






public class SomeServiceImpl {

private SomeDAOImpl someDAOImpl;
private SomeIndex someIndex;
public void setSomeDAOImpl(SomeDAOImpl someDAOImpl) {
    this.someDAOImpl = someDAOImpl;
}

    public SomeServiceImpl (){
     someIndex; = AFinalClass.init();
     setSomeDAOImpl(new SomeDAOImpl())  
   }
}

I want to prevent SomeServiceImpl() to getting called. Please let me know if there is any way to fix this. Can I mock constructor - But the SomeServiceImpl() gets called before testSomeMethod().

Answer 1

The normal solution around static method calls is to introduce a Factory.

Instead of

public class Example {
    private void foo() {
        Instant now = Instant.now();
    }
}

use

public class Example {

    private final Supplier<Instant> instantSupplier;

    public Example(Supplier<Instant> instantSupplier) {
        this.instantSupplier = instantSupplier;
    }

    public void foo() {
        Instant now = instantSupplier.get();
        System.out.println(now);
    }
}

Now you can mock the creation of the Instant.

@RunWith(MockitoJUnitRunner.class)
public class ExampleTest {

    @Mock
    Supplier<Instant> instantSupplier;

    @Test
    public void test() {
        Instant myNow = Instant.parse("2007-12-03T10:15:30.00Z");
        when(instantSupplier.get()).thenReturn(myNow);

        new Example(instantSupplier).foo();
    }

}

Output:

2007-12-03T10:15:30Z