lesson6.md

Lesson 6: Mockito Annotations

Overview

We will use annotations provided by Mockito to get rid of the redundant code and make our tests more readable.

Demonstrated Concepts

@Mock

The @Mock annotation is used to create a mock without calling the Mockito.mock method.

We can create the mocks outside the test method using the @Mock annotation as follows:

@Mock
StudentDao studentDaoMock;

By using the @Mock annotation, we will create the mock once instead of creating it in every test.

@InjectMocks

The @InjectMocks annotation automatically injects a mock object into the object being tested.

We can do the dependency injection outside the test method and use the @InjectMocks annotation as follows:

@InjectMocks
StudentService studentService;

The tests become shorter when we remove the create and inject mock steps from the test method. We can further shorten the method by making the total variable inline. For comparison, a test written with and without annotations is shown below:

• Test written without annotations

  @Test
  void testFindTotal() {
      StudentDao studentDaoMock = mock(StudentDao.class);
      when(studentDaoMock.getMarks()).thenReturn(new int[] {15, 20, 5});
      
      StudentService studentService = new StudentService(studentDaoMock);
      int total = studentService.findTotal();
      assertEquals(40, total);
  }

• Test written with annotations

  @Mock
  StudentDao studentDaoMock;
  
  @InjectMocks
  StudentService studentService;
  
  @Test
  void testFindTotal() {
      when(studentDaoMock.getMarks()).thenReturn(new int[] {15, 20, 5});
      assertEquals(40, studentService.findTotal());
  }

@ExtendWith

When the @Mock annotation is used, by default, JUnit does not evaluate it. We need to use the @ExtendWith annotation and pass MockitoExtension.class as an argument to integrate Mockito with the JUnit 5 extension model.

MockitoExtension enables the evaluation of the @Mock annotations to initialize mocks, which was previously done using the Mockito.mock method.

Using the Mockito extension, mocks are initialized before each test method and validation is performed after each test method to check if the mock was used in the method.

@ExtendWith(MockitoExtension.class)