org.mockito
Annotation Type InjectMocks

@Documented
@Target(value=FIELD)
@Retention(value=RUNTIME)
public @interface InjectMocks

• Allows shorthand mock and spy injection.
• Minimizes repetitive mock and spy injection.

Mockito will try to inject mocks only either by constructor injection, setter injection, or property injection in order and as described below. If any of the following strategy fail, then Mockito won't report failure; i.e. you will have to provide dependencies yourself.

1. Constructor injection; the biggest constructor is chosen, then arguments are resolved with mocks declared in the test only.

   Note: If arguments can not be found, then null is passed. If non-mockable types are wanted, then constructor injection won't happen. In these cases, you will have to satisfy dependencies yourself.

2. Property setter injection; mocks will first be resolved by type, then (using name if there is several property of the same type).

   Note: If @InjectMocks instance wasn't initialized before and have a no-arg constructor, then it will be initialized with this constructor.

3. Field injection; mocks will first be resolved by type, then (using name if there is several property of the same type).

   Note: If @InjectMocks instance wasn't initialized before and have a no-arg constructor, then it will be initialized with this constructor.

Example:

   public class ArticleManagerTest extends SampleBaseTestCase {

       @Mock private ArticleCalculator calculator;
       @Mock private ArticleDatabase database;
       @Spy private UserProvider userProvider = new ConsumerUserProvider();

       @InjectMocks private ArticleManager manager;

       @Test public void shouldDoSomething() {
           manager.initiateArticle();
           verify(database).addListener(any(ArticleListener.class));
       }
   }

   public class SampleBaseTestCase {

       @Before public void initMocks() {
           MockitoAnnotations.initMocks(this);
       }
   }
 

In the above example the field ArticleManager annotated with @InjectMocks can have a parameterized constructor only or a no-arg constructor only, or both. All these constructors can be package protected, protected or private, however Mockito cannot instantiate inner classes, local classes, abstract classes and of course interfaces.

The same stands for setters or fields, they can be declared with private visibility, Mockito will see them through reflection. However fields that are static or final will be ignored.

So on the field that needs injection, for example constructor injection will happen here :

   public class ArticleManager {
       ArticleManager(ArticleCalculator calculator, ArticleDatabase database) {
           // parameterized constructor
       }
   }
 

Property setter injection will happen here :

   public class ArticleManager {
       ArticleManager() {
           // no-arg constructor
       }

       void setDatabase(ArticleDatabase database) {
           // setter
       }
   }
 

Field injection will be used here :

   public class ArticleManager {
       private ArticleDatabase database;
       private ArticleCalculator calculator;
   }
 

And finally, no injection will happen on the type in this case:

   public class ArticleManager {
       private ArticleDatabase database;
       private ArticleCalculator calculator;

       ArticleManager(ArticleObserver observer, boolean flag) {
           // observer is not declared in the test above.
           // flag is not mockable anyway
       }
   }
 

Again, note that @InjectMocks will only inject mocks/spies created using the @Spy or @Mock annotation.

MockitoAnnotations.initMocks(this) method has to called to initialize annotated objects. A MockitoJUnitRunner can also be used to initialize mocks instead of the @Before approach.

In above example, initMocks() is called in @Before (JUnit4) method of test's base class. For JUnit3 initMocks() can go to setup() method of a base class. You can also put initMocks() in your JUnit runner (@RunWith) or use built-in runners: MockitoJUnitRunner