Mockito Inject real objects into private Autowired fields

Question

I m using Mockito s  Mock and  InjectMocks annotations to inject dependencies into private fields which are annotated with Spring s  Autowired    RunWith MockitoJUnitRunner class  public class DemoTest        Mock     private SomeService service        InjectMocks     private Demo demo                     and  public class Demo         Autowired     private SomeService service                     Now I would like to also inject real objects into private  Autowired fields  without setters   Is this possible or is the mechanism limited to injecting Mocks only

User · Answer

Mockito is not a DI framework and even DI frameworks encourage constructor injections over field injections.
So you just declare a constructor to set dependencies of the class under test :

@Mock
private SomeService serviceMock;

private Demo demo;

/* ... */
@BeforeEach
public void beforeEach(){
   demo = new Demo(serviceMock);
}

Using Mockito spy for the general case is a terrible advise. It makes the test class brittle, not straight and error prone : What is really mocked ? What is really tested ?
@InjectMocks and @Spy also hurts the overall design since it encourages bloated classes and mixed responsibilities in the classes.
Please read the spy() javadoc before using that blindly (emphasis is not mine) :

Creates a spy of the real object. The spy calls real methods unless they are stubbed. Real spies should be used carefully and occasionally, for example when dealing with legacy code.

As usual you are going to read the partial mock warning: Object oriented programming tackles complexity by dividing the complexity into separate, specific, SRPy objects. How does partial mock fit into this paradigm? Well, it just doesn't... Partial mock usually means that the complexity has been moved to a different method on the same object. In most cases, this is not the way you want to design your application.

However, there are rare cases when partial mocks come handy: dealing with code you cannot change easily (3rd party interfaces, interim refactoring of legacy code etc.) However, I wouldn't use partial mocks for new, test-driven & well-designed code.

User · Answer

Use  Spy annotation   RunWith MockitoJUnitRunner class  public class DemoTest        Spy     private SomeService service   new RealServiceImpl          InjectMocks     private Demo demo                     Mockito will consider all fields having  Mock or  Spy annotation as potential candidates to be injected into the instance annotated with  InjectMocks annotation  In the above case  RealServiceImpl  instance will get injected into the  demo   For more details refer  Mockito-home   Spy   Mock

User · Answer

In Addition to  Dev Blanked answer  if you want to use an existing bean that was created by Spring the code can be modified to    RunWith MockitoJUnitRunner class  public class DemoTest         Inject     private ApplicationContext ctx        Spy     private SomeService service        InjectMocks     private Demo demo        Before     public void setUp            service   ctx getBean SomeService class                            This way you don t need to change your code  add another constructor  just to make the tests work

User · Answer

I know this is an old question  but we were faced with the same problem when trying to inject Strings  So we invented a JUnit5 Mockito extension that does exactly what you want  https   github com exabrial mockito-object-injection  EDIT    InjectionMap  private Map lt String  Object gt  injectionMap   new HashMap lt  gt        BeforeEach  public void beforeEach   throws Exception     injectionMap put  securityEnabled   Boolean TRUE         AfterEach  public void afterEach   throws Exception     injectionMap clear

User · Answer

In Spring there is a dedicated utility called ReflectionTestUtils for this purpose  Take the specific instance and inject into the the field     Spy     Mock      InjectMock Foo foo    BeforeEach void  before       ReflectionTestUtils setField foo  bar   new BarImpl        bar  is private field

[java] Mockito: Inject real objects into private @Autowired fields

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