@Mock, @Spy, @Captor and @InjectMocks

http://www.baeldung.com/mockito-annotations

1. Overview

In this tutorial, we’ll cover all the annotations in the Mockito library–@Mock, @Spy, @Captorand @InjectMocks.

2. Enable Mockito Annotations

First – let’s see how to enable the use of annotations with Mockito tests.

In order for these annotations to be enabled, we’ll need to annotate the JUnit test with a runner–MockitoJUnitRunneras in the following example:

@RunWith(MockitoJUnitRunner.class)public class MockitoAnnotationTest {    ...}

Alternatively we can enable these annotations programmaticallyas well, by invokingMockitoAnnotations.initMocks()as in the following example:

@Beforepublic void init() {    MockitoAnnotations.initMocks(this);}

3. @MockAnnotation

The most used widely used annotation in Mockito is @Mock. We can use @Mockto create and inject mocked instances without having to call Mockito.mockmanually.

In the following example – we’ll create a mocked ArrayListwith the manual way without using@Mockannotation:

@Testpublic void whenNotUseMockAnnotation_thenCorrect() {  List mockList = Mockito.mock(ArrayList.class);    mockList.add("one");  Mockito.verify(mockList).add("one");  assertEquals(0, mockList.size());  Mockito.when(mockList.size()).thenReturn(100);  assertEquals(100, mockList.size());}

And now we’ll do the same but we’ll inject the mock using the @Mockannotation:

@MockList<String> mockedList;@Testpublic void whenUseMockAnnotation_thenMockIsInjected() {  mockedList.add("one");  Mockito.verify(mockedList).add("one");  assertEquals(0, mockedList.size());  Mockito.when(mockedList.size()).thenReturn(100);  assertEquals(100, mockedList.size());}

Note how – in both examples, we’re interacting with the mock and verifying some of these interactions – just to make sure that the mock is behaving correctly.

4. @SpyAnnotation

Now – let’s see how to use @Spyannotation to spy on an existing instance.

In the following example – we create a spy of a Listwith the old way without using@Spyannotation:

@Testpublic void whenNotUseSpyAnnotation_thenCorrect() {  List<String> spyList = Mockito.spy(new ArrayList<String>());    spyList.add("one");  spyList.add("two");  Mockito.verify(spyList).add("one");  Mockito.verify(spyList).add("two");  assertEquals(2, spyList.size());  Mockito.doReturn(100).when(spyList).size();  assertEquals(100, spyList.size());}

Let’s now do the same – spy on the list – but do so using the @Spyannotation:

@SpyList<String> spiedList = new ArrayList<String>();@Testpublic void whenUseSpyAnnotation_thenSpyIsInjected() {  spiedList.add("one");  spiedList.add("two");  Mockito.verify(spiedList).add("one");  Mockito.verify(spiedList).add("two");  assertEquals(2, spiedList.size());  Mockito.doReturn(100).when(spiedList).size();  assertEquals(100, spiedList.size());}

Note how, as before – we’re interacting with the spy here to make sure that it behaves correctly. In this example we:

• Used the realmethod spiedList.add()to add elements to thespiedList.
• Stubbedthe method spiedList.size()to return 100instead of2using Mockito.doReturn().

5. @CaptorAnnotation

Next – let’s see how to use the @Captorannotation to create an ArgumentCaptorinstance.

In the following example – we create an ArgumentCaptorwith the old way without using@Captorannotation:

@Testpublic void whenNotUseCaptorAnnotation_thenCorrect() {  List mockList = Mockito.mock(List.class);  ArgumentCaptor<String> arg = ArgumentCaptor.forClass(String.class);  mockList.add("one");  Mockito.verify(mockList).add(arg.capture());  assertEquals("one", arg.getValue());}

Let’s now make use of @Captor for the same purpose – to create anArgumentCaptorinstance:

@MockList mockedList;@Captor ArgumentCaptor argCaptor;@Testpublic void whenUseCaptorAnnotation_thenTheSam() {    mockedList.add("one");    Mockito.verify(mockedList).add(argCaptor.capture());    assertEquals("one", argCaptor.getValue());}

Notice how the test becomes simpler and more readable when we take out the configuration logic.

6. @InjectMocksAnnotation

Now – let’s discuss how to use @InjectMocksannotation – to inject mock fields into the tested object automatically.

In the following example – we use @InjectMocksto inject the mock wordMapinto the MyDictionary dic:

@MockMap<String, String> wordMap;@InjectMocksMyDictionary dic = new MyDictionary();@Testpublic void whenUseInjectMocksAnnotation_thenCorrect() {    Mockito.when(wordMap.get("aWord")).thenReturn("aMeaning");    assertEquals("aMeaning", dic.getMeaning("aWord"));}

And here is the class MyDictionary:

public class MyDictionary {  Map<String, String> wordMap;  public MyDictionary() {    wordMap = new HashMap<String, String>();  }  public void add(final String word, final String meaning) {    wordMap.put(word, meaning);  }  public String getMeaning(final String word) {    return wordMap.get(word);  }}

7. Notes

Finally – here is some notes about Mockito annotations:

• Use annotation to minimize repetitive mock creation code
• Use annotation to make the test more readable
• Use @InjectMocksto inject both @Spyand @Mockinstances

8. Conclusion

In this quick tutorial, we learned the basics of annotations in the Mockito library.

The implementation of all these examples and code snippets can be found in my Mockito github project – this is an Eclipse based project, so it should be easy to import and run as it is.

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