Mockito for Unit Testing

1. Introduction

Mockito is a popular mocking framework for Java that allows you to create mock objects for unit testing. It enables the isolation of the class under test by simulating its dependencies.

2. Key Concepts

3. Setup

        // Maven Dependency for Mockito
        <dependency>
            <groupId>org.mockito</groupId>
            <artifactId>mockito-core</artifactId>
            <version>3.12.4</version>
            <scope>test</scope>
        </dependency>
        

4. Basic Mocking

Mocking a class with Mockito is straightforward. Here's an example:

        import static org.mockito.Mockito.*;

        public class UserServiceTest {
            @Test
            public void testGetUser() {
                UserRepository mockRepo = mock(UserRepository.class);
                User user = new User("John");
                when(mockRepo.findUser("John")).thenReturn(user);

                UserService userService = new UserService(mockRepo);
                User result = userService.getUser("John");

                assertEquals("John", result.getName());
            }
        }
        

5. Advanced Features

Mockito offers advanced functionalities such as argument matchers, verification, and exceptions:

        // Using argument matchers
        when(mockRepo.findUser(anyString())).thenReturn(user);

        // Verifying interactions
        verify(mockRepo).findUser("John");

        // Stubbing to throw exceptions
        when(mockRepo.findUser("Invalid")).thenThrow(new UserNotFoundException());
        

6. Best Practices

• Keep tests focused on one behavior.
• Use meaningful names for mocks and tests.
• Limit the number of interactions in your tests.
• Use @Mock and @InjectMocks annotations for cleaner tests.

7. FAQ