Spring BootIntermediate9 min read2026-03-01

Spring Boot Unit Testing with JUnit 5 & Mockito

Q: What is the difference between @Mock and @MockBean?

@Mock is a pure Mockito annotation that does not involve Spring. @MockBean registers the mock directly into the Spring ApplicationContext.

Write clean, robust unit and integration tests for Spring Boot controllers and services using Mockito and MockMvc.

Prerequisites

Spring Boot basics
JUnit 5 fundamentals

1. Service Unit Test with @ExtendWith(MockitoExtension.class)

Test service business logic in complete isolation without loading the heavyweight Spring context.

java

@ExtendWith(MockitoExtension.class)
class ArticleServiceTest {
    @Mock
    private ArticleRepository repository;

    @InjectMocks
    private ArticleService service;

    @Test
    void shouldReturnArticleWhenFound() {
        Article article = new Article("Test Title", "Content");
        when(repository.findById(1L)).thenReturn(Optional.of(article));

        Article result = service.getById(1L);
        assertThat(result.getTitle()).isEqualTo("Test Title");
    }
}

2. Controller Web Slice Test with @WebMvcTest

Test HTTP endpoints, JSON serialization, and status codes using MockMvc.

java

@WebMvcTest(ArticleController.class)
class ArticleControllerTest {
    @Autowired
    private MockMvc mockMvc;

    @MockBean
    private ArticleService service;

    @Test
    void shouldReturnOkStatus() throws Exception {
        mockMvc.perform(get("/api/v1/articles"))
            .andExpect(status().isOk());
    }
}

Best Practices & Architecture Advice

Prefer pure unit tests with Mockito for fast CI feedback (< 1 second).
Use @WebMvcTest for controller validation and status tests instead of full @SpringBootTest.

Common Mistakes to Watch Out For

•Using @SpringBootTest on every test class, causing slow test suites that take 10+ minutes to execute.

Frequently Asked Questions

What is the difference between @Mock and @MockBean?