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/instancio.md
+++ b/skills/spring-boot-testing/references/instancio.md
@@ -0,0 +1,230 @@
+# Instancio
+
+Generate complex test objects automatically. Use when entities/DTOs have 3+ properties.
+
+## When to Use
+
+- Objects with **3 or more properties**
+- Setting up test data for repositories
+- Creating DTOs for controller tests
+- Avoiding repetitive builder/setter calls
+
+## Dependency
+
+```xml
+<dependency>
+  <groupId>org.instancio</groupId>
+  <artifactId>instancio-junit</artifactId>
+  <version>5.5.1</version>
+  <scope>test</scope>
+</dependency>
+```
+
+## Basic Usage
+
+### Simple Object
+
+```java
+final var order = Instancio.create(Order.class);
+// All fields populated with random data
+```
+
+### List of Objects
+
+```java
+final var orders = Instancio.ofList(Order.class).size(5).create();
+// 5 orders with random data
+```
+
+## Customizing Values
+
+### Set Specific Fields
+
+```java
+final var order = Instancio.of(Order.class)
+  .set(field(Order::getStatus), "PENDING")
+  .set(field(Order::getTotal), new BigDecimal("99.99"))
+  .create();
+```
+
+### Supply Generated Values
+
+```java
+final var order = Instancio.of(Order.class)
+  .supply(field(Order::getEmail), () -> "user" + UUID.randomUUID() + "@test.com")
+  .create();
+```
+
+### Ignore Fields
+
+```java
+final var order = Instancio.of(Order.class)
+  .ignore(field(Order::getId)) // Let DB generate
+  .create();
+```
+
+## Complex Objects
+
+### Nested Objects
+
+```java
+final var order = Instancio.of(Order.class)
+  .set(field(Order::getCustomer), Instancio.create(Customer.class))
+  .set(field(Order::getItems), Instancio.ofList(OrderItem.class).size(3).create())
+  .create();
+```
+
+### All Fields Random
+
+```java
+// When you need fully random but valid data
+final var randomOrder = Instancio.create(Order.class);
+// Customer, items, addresses - all populated
+```
+
+## Spring Boot Integration
+
+### Repository Test Setup
+
+```java
+@DataJpaTest
+@AutoConfigureTestDatabase
+@Testcontainers
+class OrderRepositoryTest {
+  
+  @Container
+  @ServiceConnection
+  static PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:18");
+  
+  @Autowired
+  private OrderRepository orderRepository;
+  
+  @Test
+  void shouldFindOrdersByStatus() {
+    // Given: Create 10 random orders with PENDING status
+    final var orders = Instancio.ofList(Order.class)
+      .size(10)
+      .set(field(Order::getStatus), "PENDING")
+      .create();
+    
+    orderRepository.saveAll(orders);
+    
+    // When
+    final var found = orderRepository.findByStatus("PENDING");
+    
+    // Then
+    assertThat(found).hasSize(10);
+  }
+}
+```
+
+### Controller Test Setup
+
+```java
+@WebMvcTest(OrderController.class)
+class OrderControllerTest {
+  
+  @Autowired
+  private MockMvcTester mvc;
+  
+  @MockitoBean
+  private OrderService orderService;
+  
+  @Test
+  void shouldReturnOrder() {
+    // Given: Random order with specific ID
+    Order order = Instancio.of(Order.class)
+      .set(field(Order::getId), 1L)
+      .create();
+    
+    given(orderService.findById(1L)).willReturn(order);
+    
+    // When/Then
+    assertThat(mvc.get().uri("/orders/1"))
+      .hasStatus(HttpStatus.OK)
+      .bodyJson()
+      .convertTo(OrderResponse.class)
+      .satisfies(response -> {
+        assertThat(response.getId()).isEqualTo(1L);
+      });
+  }
+}
+```
+
+## Patterns
+
+### Builder Pattern Alternative
+
+```java
+// Instead of:
+Order order = Order.builder()
+  .id(1L)
+  .status("PENDING")
+  .customer(Customer.builder().name("John").build())
+  .items(List.of(
+    OrderItem.builder().product("A").price(10).build(),
+    OrderItem.builder().product("B").price(20).build()
+  ))
+  .build();
+
+// Use:
+Order order = Instancio.of(Order.class)
+  .set(field(Order::getId), 1L)
+  .set(field(Order::getStatus), "PENDING")
+  .create();
+// Customer and items auto-generated
+```
+
+### Seeded Data
+
+```java
+// Consistent "random" data for reproducible tests
+Order order = Instancio.of(Order.class)
+  .withSeed(12345L)
+  .create();
+// Same data every test run with seed 12345
+```
+
+## Common Patterns
+
+### Email Generation
+
+```java
+String email = Instancio.gen().net().email();
+```
+
+### Date Generation
+
+```java
+LocalDateTime createdAt = Instancio.gen().temporal()
+  .localDateTime()
+  .past()
+  .create();
+```
+
+### String Patterns
+
+```java
+String phone = Instancio.gen().text().pattern("+1-###-###-####");
+```
+
+## Comparison
+
+| Approach | Lines of Code | Maintainability |
+| -------- | ------------- | --------------- |
+| Manual setters | 10-20 | Low |
+| Builder pattern | 5-10 | Medium |
+| **Instancio** | 2-5 | **High** |
+
+## Best Practices
+
+1. **Use for 3+ property objects** - Not worth it for simple objects
+2. **Set only what's relevant** - Let Instancio fill the rest
+3. **Use with Testcontainers** - Great for database seeding
+4. **Set IDs explicitly** - When testing specific scenarios
+5. **Ignore auto-generated fields** - Like createdAt, updatedAt
+
+## Links
+
+- [Instancio Documentation](https://www.instancio.org/)
+- [JUnit 5 Extension](https://www.instancio.org/user-guide/#junit-integration)