feat: add spring-boot-testing skill for Spring Boot 4.0 (#1085)

- Introduced MockMvcTester for AssertJ-style assertions in Spring MVC testing. - Added @RestClientTest for testing REST clients with MockRestServiceServer. - Implemented RestTestClient as a modern alternative to TestRestTemplate. - Documented migration steps from Spring Boot 3.x to 4.0, including dependency and annotation changes. - Created an overview of test slices to guide testing strategies. - Included Testcontainers setup for JDBC testing with PostgreSQL and MySQL. - Enhanced @WebMvcTest documentation with examples for various HTTP methods and validation.
2026-03-21 00:25:13 +00:00 · 2026-03-20 04:54:37 +05:30
parent ee71c0689c
commit e4fc57f204
16 changed files with 3171 additions and 0 deletions
--- a/skills/spring-boot-testing/references/test-slices-overview.md
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+# Test Slices Overview
+
+Quick reference for selecting the right Spring Boot test slice.
+
+## Decision Matrix
+
+| Annotation | Use When | Loads | Speed |
+| ---------- | -------- | ----- | ----- |
+| **None** (plain JUnit) | Testing pure business logic | Nothing | Fastest |
+| `@WebMvcTest` | Controller + HTTP layer | Controllers, MVC, Jackson | Fast |
+| `@DataJpaTest` | Repository queries | Repositories, JPA, DataSource | Fast |
+| `@RestClientTest` | REST client code | RestTemplate/RestClient, Jackson | Fast |
+| `@JsonTest` | JSON serialization | ObjectMapper only | Fastest slice |
+| `@WebFluxTest` | Reactive controllers | Controllers, WebFlux | Fast |
+| `@DataJdbcTest` | JDBC repositories | Repositories, JDBC | Fast |
+| `@DataMongoTest` | MongoDB repositories | Repositories, MongoDB | Fast |
+| `@DataRedisTest` | Redis repositories | Repositories, Redis | Fast |
+| `@SpringBootTest` | Full integration | Entire application | Slow |
+
+## Selection Guide
+
+### Use NO Annotation (Plain Unit Test)
+
+```java
+class PriceCalculatorTest {
+  private PriceCalculator calculator = new PriceCalculator();
+  
+  @Test
+  void shouldApplyDiscount() {
+    var result = calculator.applyDiscount(100, 0.1);
+    assertThat(result).isEqualTo(new BigDecimal("90.00"));
+  }
+}
+```
+
+**When**: Pure business logic, no dependencies or simple dependencies mockable via constructor injection.
+
+### Use @WebMvcTest
+
+```java
+@WebMvcTest(OrderController.class)
+class OrderControllerTest {
+  @Autowired private MockMvcTester mvc;
+  @MockitoBean private OrderService orderService;
+}
+```
+
+**When**: Testing request mapping, validation, JSON mapping, security, filters.
+
+**What you get**: MockMvc, ObjectMapper, Spring Security (if present), exception handlers.
+
+### Use @DataJpaTest
+
+```java
+@DataJpaTest
+@AutoConfigureTestDatabase(replace = AutoConfigureTestDatabase.Replace.NONE)
+@Testcontainers
+class OrderRepositoryTest {
+  @Container
+  static PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:18");
+}
+```
+
+**When**: Testing custom JPA queries, entity mappings, transaction behavior, cascade operations.
+
+**What you get**: Repository beans, EntityManager, TestEntityManager, transaction support.
+
+### Use @RestClientTest
+
+```java
+@RestClientTest(WeatherService.class)
+class WeatherServiceTest {
+  @Autowired private WeatherService weatherService;
+  @Autowired private MockRestServiceServer server;
+}
+```
+
+**When**: Testing REST clients that call external APIs.
+
+**What you get**: MockRestServiceServer to stub HTTP responses.
+
+### Use @JsonTest
+
+```java
+@JsonTest
+class OrderJsonTest {
+  @Autowired private JacksonTester<Order> json;
+}
+```
+
+**When**: Testing custom serializers/deserializers, complex JSON mapping.
+
+### Use @SpringBootTest
+
+```java
+@SpringBootTest(webEnvironment = WebEnvironment.RANDOM_PORT)
+@AutoConfigureRestTestClient
+class OrderIntegrationTest {
+  @Autowired private RestTestClient restClient;
+}
+```
+
+**When**: Testing full request flow, security filters, database interactions together.
+
+**What you get**: Full application context, embedded server (optional), real beans.
+
+## Common Mistakes
+
+1. **Using @SpringBootTest for everything** - Slows down your test suite unnecessarily
+2. **@WebMvcTest without mocking services** - Causes context loading failures
+3. **@DataJpaTest with @MockBean** - Defeats the purpose (you want real repositories)
+4. **Multiple slices in one test** - Each slice is a separate test class
+
+## Java 25 Features in Tests
+
+### Records for Test Data
+
+```java
+record OrderRequest(String product, int quantity) {}
+record OrderResponse(Long id, String status, BigDecimal total) {}
+```
+
+### Pattern Matching in Tests
+
+```java
+@Test
+void shouldHandleDifferentOrderTypes() {
+  var order = orderService.create(new OrderRequest("Product", 2));
+  
+  switch (order) {
+    case PhysicalOrder po -> assertThat(po.getShippingAddress()).isNotNull();
+    case DigitalOrder do_ -> assertThat(do_.getDownloadLink()).isNotNull();
+    default -> throw new IllegalStateException("Unknown order type");
+  }
+}
+```
+
+### Text Blocks for JSON
+
+```java
+@Test
+void shouldParseComplexJson() {
+  var json = """
+    {
+      "id": 1,
+      "status": "PENDING",
+      "items": [
+        {"product": "Laptop", "price": 999.99},
+        {"product": "Mouse", "price": 29.99}
+      ]
+    }
+    """;
+  
+  assertThat(mvc.post().uri("/orders")
+    .contentType(APPLICATION_JSON)
+    .content(json))
+    .hasStatus(CREATED);
+}
+```
+
+### Sequenced Collections
+
+```java
+@Test
+void shouldReturnOrdersInSequence() {
+  var orders = orderRepository.findAll();
+  
+  assertThat(orders.getFirst().getStatus()).isEqualTo("NEW");
+  assertThat(orders.getLast().getStatus()).isEqualTo("COMPLETED");
+  assertThat(orders.reversed().getFirst().getStatus()).isEqualTo("COMPLETED");
+}
+```
+
+## Dependencies by Slice
+
+```xml
+<!-- WebMvcTest -->
+<dependency>
+  <groupId>org.springframework.boot</groupId>
+  <artifactId>spring-boot-starter-webmvc-test</artifactId>
+  <scope>test</scope>
+</dependency>
+
+<!-- DataJpaTest -->
+<dependency>
+  <groupId>org.springframework.boot</groupId>
+  <artifactId>spring-boot-starter-data-jpa</artifactId>
+</dependency>
+
+<!-- RestClientTest -->
+<dependency>
+  <groupId>org.springframework.boot</groupId>
+  <artifactId>spring-boot-starter-restclient-test</artifactId>
+  <scope>test</scope>
+</dependency>
+
+<!-- Testcontainers -->
+<dependency>
+  <groupId>org.springframework.boot</groupId>
+  <artifactId>spring-boot-testcontainers</artifactId>
+  <scope>test</scope>
+</dependency>
+```