Spring Boot Test Slices: @WebMvcTest and @DataJpaTest

What Are Test Slices?

@WebMvcTest: Controller Layer Only

@WebMvcTest(UserController.class)
class UserControllerTest {
    @Autowired MockMvc mockMvc;
    @MockBean UserService userService;
    @Test
    void get_user_returns_200() throws Exception {
        given(userService.findById(1L)).willReturn(new UserDto(1L, "Alice"));
        mockMvc.perform(get("/api/users/1"))
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.name").value("Alice"));
    }
}

MockMvc Request Building

mockMvc.perform(post("/api/users")
        .contentType(MediaType.APPLICATION_JSON)
        .content("""{"name":"Bob","email":"bob@example.com"}"""))
    .andExpect(status().isCreated())
    .andExpect(header().exists("Location"));

Testing Validation in @WebMvcTest

mockMvc.perform(post("/api/users")
        .contentType(MediaType.APPLICATION_JSON)
        .content("""{"name":"","email":"bad"}"""))
    .andExpect(status().isBadRequest())
    .andExpect(jsonPath("$.errors.name").exists());

@DataJpaTest: Repository Layer Only

@DataJpaTest
class UserRepositoryTest {
    @Autowired UserRepository repo;
    @Autowired TestEntityManager em;
    @Test
    void find_by_email() {
        em.persist(new User("Alice", "alice@example.com"));
        em.flush();
        Optional<User> found = repo.findByEmail("alice@example.com");
        assertTrue(found.isPresent());
    }
}

TestEntityManager

User saved = em.persistAndFlush(new User("Bob", "bob@example.com"));
assertNotNull(saved.getId());
em.clear(); // detach all to force a real DB read
User fromDb = repo.findById(saved.getId()).orElseThrow();
assertEquals("Bob", fromDb.getName());

@DataJpaTest Rollback

@DataJpaTest  // each @Test is rolled back automatically
class OrderRepositoryTest {
    @Test @Transactional
    void count_orders_is_zero_by_default() {
        assertEquals(0, orderRepo.count());
    }
}

Replacing H2 with Real DB in @DataJpaTest

@DataJpaTest
@AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE)
class ProductRepositoryTest {
    // Uses the configured PostgreSQL, not H2
}

@JsonTest: JSON Serialization Only

@JsonTest
class UserDtoJsonTest {
    @Autowired JacksonTester<UserDto> json;
    @Test
    void serializes_correctly() throws Exception {
        UserDto dto = new UserDto(1L, "Alice", "alice@example.com");
        assertThat(json.write(dto)).hasJsonPathStringValue("$.email");
    }
}

@RestClientTest: REST Client Layer

@RestClientTest(WeatherClient.class)
class WeatherClientTest {
    @Autowired WeatherClient client;
    @Autowired MockRestServiceServer server;
    @Test
    void fetches_weather() {
        server.expect(requestTo("/api/weather")).andRespond(withSuccess("""{"temp":22}""", APPLICATION_JSON));
        Weather w = client.getWeather("Istanbul");
        assertEquals(22, w.getTemp());
    }
}

Combining Slices with @Import

@WebMvcTest(UserController.class)
@Import(SecurityConfig.class)  // load security for auth tests
class SecuredControllerTest { ... }

Quick Check

Recap