How can I mock methods of @InjectMocks class?

Main Class

@Component
public class MyHandler {

  @AutoWired
  private MyDependency myDependency;

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

  public int anotherMethod() {...}
}

Test Class

@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);
  }
}

Solution:

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)