How can I mock methods of @InjectMocks class?

Question

For example I have handler:

@Component
public class MyHandler {

  @AutoWired
  private MyDependency myDependency;

  public int someMethod() {
    ...
    return anotherMethod();
  }

  public int anotherMethod() {...}
}

to testing it I want to write something like this:

@RunWith(MockitoJUnitRunner.class}
class MyHandlerTest {

  @InjectMocks
  private MyHandler myHandler;

  @Mock
  private MyDependency myDependency;

  @Test
  public void testSomeMethod() {
    when(myHandler.anotherMethod()).thenReturn(1);
    assertEquals(myHandler.someMethod() == 1);
  }
}

But it actually calls anotherMethod() whenever I try to mock it. What should I do with myHandler to mock its methods?

If you want to test MyHandler, you shouldn't mock it's own methods (since you want to test your handler, not the mock). Is there a specific reason why you need to do so? — Nitek, Jun 11 '15 at 07:46

score 170 · Accepted Answer · edited Sep 10 '21 at 20:23

170

First of all the reason for mocking MyHandler methods can be the following: we already test anotherMethod() and it has complex logic, so why do we need to test it again (like a part of someMethod()) if we can just verify that it's calling?
We can do it through:

@RunWith(MockitoJUnitRunner.class)
class MyHandlerTest {

  @Spy  
  @InjectMocks  
  private MyHandler myHandler;  

  @Mock  
  private MyDependency myDependency;  

  @Test  
  public void testSomeMethod() {  
    doReturn(1).when(myHandler).anotherMethod();  
    assertEquals(myHandler.someMethod() == 1);  
    verify(myHandler, times(1)).anotherMethod();  
  }  
}

Note: in case of 'spying' object we need to use doReturn instead of thenReturn(little explanation is here)

edited Sep 10 '21 at 20:23

HydraHatRack

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answered Oct 05 '15 at 08:33

Vova Yatsyk

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2

It doesn't inject anything, if you use both Spy and InjectMocks annotations – ildar ishalin Sep 04 '18 at 08:19
@ildarishalin I just tried with junit 4.12 and mockito-core 2.15 and everything works – Vova Yatsyk Sep 06 '18 at 07:37
I am not sure `@Spy` and `@InjectMocks` should be used together -> https://stackoverflow.com/questions/38567326/is-it-discouraged-to-use-spy-and-injectmocks-on-the-same-field – Ghilteras Nov 13 '18 at 23:27
1

@ildarishalin maybe you got fooled by having called *both*, the mock method *and* the real method. To avoid this, you can use the "mockito old style" with doReturn()...when(). See also the gotcha under https://javadoc.io/static/org.mockito/mockito-core/3.3.1/org/mockito/Mockito.html#13 – Thomas Schütt Mar 10 '20 at 14:37
On the first line @RunWith(MockitoJUnitRunner.class} Please replace the last character '}' with ')' – Nauman Shah Oct 13 '20 at 12:21

score 10 · Answer 2 · edited Oct 15 '22 at 11:06

All answers above are really good and may be useful so make sure you study and understand these principes first before continue reading my post.

In my scenario none of advices above did work. I will post what helped me after a pretty long debugging.

If you want to call methods from tested class, the @Spy annotation is needed alongside @InjectMocks (or Mockito.spy(XXX) call or course)

The interesting part is, the order of these annotations does matter! The @Spy annotation must precede @InjectMocks annotation.

Will not work

...

@InjectMocks
@Spy
private TestedObject instance

...

Will work

...

@Spy
@InjectMocks
private TestedObject instance

...

score 4 · Answer 3 · answered Jun 11 '15 at 07:58

In your code, you are not testing MyHandler at all. You don't want to mock what you are testing, you want to call its actual methods. If MyHandler has dependencies, you mock them.

Something like this:

public interface MyDependency {
  public int otherMethod();
}

public class MyHandler {
  @AutoWired
  private MyDependency myDependency;

  public void someMethod() {
    myDependency.otherMethod();
  }
}

And in test:

private MyDependency mockDependency;
private MyHandler realHandler;

@Before
public void setup() {
   mockDependency = Mockito.mock(MyDependency.class);
   realHandler = new MyHandler();
   realhandler.setDependency(mockDependency); //but you might Springify this 
}

@Test
public void testSomeMethod() {

  //specify behaviour of mock
  when(mockDependency.otherMethod()).thenReturn(1);

  //really call the method under test
  realHandler.someMethod();
}

The point is to really call the method under test, but mock any dependencies they may have (e.g. calling method of other classes)

If those other classes are part of your application, then they'd have their own unit tests.

NOTE the above code could be shortened with more annotations, but I wanted to make it more explicit for the sake of explanation (and also I can't remember what the annotations are :) )

Creating an instance while using spring IOC. You are not benefiting from the spring IOC. Let suppose if I have to inject another service. I cannot do that. I have to create an instance. — Muhamamd Omar Muneer, Oct 18 '17 at 19:53
Be carefull with this kind of answer, there is plenty of scenario where we don't want to test the whole class but just a part. For exemple I have an inherited class from an external framework really difficult to inialize in a mock, with a very complex context. Initialize it is a pain but also not usefull to test just my function which use a very small part of this context. — amdev, Jul 16 '18 at 09:47

How can I mock methods of @InjectMocks class?

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