Spring Testing Skill

Master testing Spring Boot applications with MockMvc, TestContainers, test slices, and comprehensive testing strategies.

Overview

This skill covers the complete testing pyramid for Spring Boot applications from unit tests to integration tests.

Parameters

Name	Type	Required	Default	Validation
test_type	enum	✗	unit	unit | integration | e2e
slice	enum	✗	-	web | data | json
mock_strategy	enum	✗	mockito	mockito | mockbean | wiremock

Topics Covered

Core (Must Know)

• Test Slices: @WebMvcTest, @DataJpaTest, @JsonTest
• MockMvc: Controller testing without full server
• Mockito: Mocking dependencies

Intermediate

• TestContainers: Real database testing with Docker
• WireMock: External service mocking
• Security Testing: @WithMockUser

Advanced

• Contract Testing: Spring Cloud Contract
• Performance Testing: Response time assertions
• Custom Test Slices: Building reusable test configurations

Code Examples

WebMvcTest

@WebMvcTest(UserController.class)
class UserControllerTest {

    @Autowired
    private MockMvc mockMvc;

    @MockBean
    private UserService userService;

    @Test
    void shouldReturnUser() throws Exception {
        when(userService.findById(1L)).thenReturn(new UserResponse(1L, "John"));

        mockMvc.perform(get("/api/users/{id}", 1L))
            .andExpect(status().isOk())
            .andExpect(jsonPath("$.id").value(1))
            .andExpect(jsonPath("$.name").value("John"));
    }

    @Test
    void shouldReturn400WhenInvalid() throws Exception {
        mockMvc.perform(post("/api/users")
                .contentType(MediaType.APPLICATION_JSON)
                .content("{\"name\":\"\"}"))
            .andExpect(status().isBadRequest())
            .andExpect(jsonPath("$.errors.name").exists());
    }

    @Test
    @WithMockUser(roles = "ADMIN")
    void shouldAllowAdminAccess() throws Exception {
        mockMvc.perform(get("/api/admin/users"))
            .andExpect(status().isOk());
    }
}

DataJpaTest with TestContainers

@DataJpaTest
@AutoConfigureTestDatabase(replace = Replace.NONE)
@Testcontainers
class UserRepositoryTest {

    @Container
    @ServiceConnection
    static PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:15");

    @Autowired
    private UserRepository userRepository;

    @Autowired
    private TestEntityManager entityManager;

    @Test
    void shouldFindByEmail() {
        User user = new User("john@test.com", "John");
        entityManager.persistAndFlush(user);

        Optional<User> found = userRepository.findByEmail("john@test.com");

        assertThat(found).isPresent()
            .hasValueSatisfying(u -> assertThat(u.getName()).isEqualTo("John"));
    }
}

Integration Test

@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
@Testcontainers
class OrderIntegrationTest {

    @Container
    @ServiceConnection
    static PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:15");

    @Autowired
    private TestRestTemplate restTemplate;

    @Autowired
    private OrderRepository orderRepository;

    @BeforeEach
    void setUp() {
        orderRepository.deleteAll();
    }

    @Test
    void shouldCreateOrder() {
        CreateOrderRequest request = new CreateOrderRequest("item1", 2);

        ResponseEntity<OrderResponse> response = restTemplate
            .postForEntity("/api/orders", request, OrderResponse.class);

        assertThat(response.getStatusCode()).isEqualTo(HttpStatus.CREATED);
        assertThat(response.getBody().id()).isNotNull();
        assertThat(orderRepository.findAll()).hasSize(1);
    }
}

WireMock for External Services

@SpringBootTest
@WireMockTest(httpPort = 8089)
class PaymentServiceTest {

    @Autowired
    private PaymentService paymentService;

    @Test
    void shouldProcessPayment() {
        stubFor(post("/payments")
            .willReturn(okJson("{\"transactionId\":\"TXN-123\",\"status\":\"SUCCESS\"}")));

        PaymentResult result = paymentService.charge(new BigDecimal("99.99"));

        assertThat(result.transactionId()).isEqualTo("TXN-123");
        assertThat(result.status()).isEqualTo("SUCCESS");
    }
}

Troubleshooting

Failure Modes

Issue	Diagnosis	Fix
Context not loading	Missing config	Add @TestConfiguration
MockBean not working	Wrong package	Check component scan
TestContainers timeout	Docker not running	Start Docker daemon

Debug Checklist

□ Check test annotations (@SpringBootTest, @WebMvcTest)
□ Verify MockBean setup
□ Confirm TestContainers are starting
□ Check application-test.yml is loaded
□ Enable debug logging for tests

Test Configuration

# application-test.yml
spring:
  jpa:
    show-sql: true
logging:
  level:
    org.springframework.test: DEBUG
    org.testcontainers: DEBUG

Usage

Skill("spring-testing")

Version History

Version	Date	Changes
2.0.0	2024-12-30	TestContainers 1.19+, WireMock 3.x patterns
1.0.0	2024-01-01	Initial release