8.1 Testing Strategy & Test Slices

← Back to Chapter 8: Testing, Deployment & Production-Ready Spring Boot

A balanced testing pyramid combines fast unit tests, focused test slices, and end-to-end integration tests.

---

1. The Spring Boot Testing Pyramid

                / \
               /   \      End-to-End (@SpringBootTest)
              /     \     - Slowest, spins up full ApplicationContext
             /-------\
            /         \   Test Slices (@WebMvcTest, @DataJpaTest)
           /           \  - Medium speed, loads only 1 architectural tier
          /-------------\
         /               \ Pure Unit Tests (JUnit 5 + Mockito)
        /                 \- Fastest (milliseconds), NO Spring context
       /-------------------\

---

2. Spring Test Slices

Instead of bootstrapping hundreds of services and repositories, Test Slices instantiate only components relevant to the layer under test:

Test Slice Annotation	What It Loads	Typical Collaborators Mocked
@WebMvcTest(UserController.class)	@Controller, @RestControllerAdvice, Filter, MockMvc	Service dependencies (@MockBean)
@DataJpaTest	@Entity, JpaRepository, embedded DB, SQL logging	Web layer, Services (completely excluded)
@JsonTest	Jackson serializers and deserializers	Validates JSON formatting and dates

Controller Slice Test with MockMvc:

@WebMvcTest(UserController.class)
class UserControllerTest {

    @Autowired
    private MockMvc mockMvc;

    @MockBean
    private UserService userService;

    @Test
    void shouldReturnUserWhenFound() throws Exception {
        UserDTO mockUser = new UserDTO(1L, "Sarwvidya", "sarvy@codewithsarvy.dev");
        Mockito.when(userService.findById(1L)).thenReturn(mockUser);

        mockMvc.perform(get("/api/v1/users/1")
                .accept(MediaType.APPLICATION_JSON))
                .andExpect(status().isOk())
                .andExpect(jsonPath("$.id").value(1))
                .andExpect(jsonPath("$.fullName").value("Sarwvidya"))
                .andExpect(jsonPath("$.email").value("sarvy@codewithsarvy.dev"));
    }
}

---

3. Full Integration Testing with @SpringBootTest

@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
@AutoConfigureMockMvc
class UserIntegrationTest {

    @Autowired
    private MockMvc mockMvc;

    @Autowired
    private UserRepository userRepository;

    @Test
    void endToEndUserRegistration() throws Exception {
        String payload = """
            {
                "email": "test@codewithsarvy.dev",
                "fullName": "Test User",
                "password": "Password123!"
            }
        """;

        mockMvc.perform(post("/api/v1/users")
                .contentType(MediaType.APPLICATION_JSON)
                .content(payload))
                .andExpect(status().isCreated());

        assertTrue(userRepository.findByEmail("test@codewithsarvy.dev").isPresent());
    }
}