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1---
2paths:
3  - "**/*.java"
4---
5# Java Testing
6 
7> This file extends [common/testing.md](../common/testing.md) with Java-specific content.
8 
9## Test Framework
10 
11- **JUnit 5** (`@Test`, `@ParameterizedTest`, `@Nested`, `@DisplayName`)
12- **AssertJ** for fluent assertions (`assertThat(result).isEqualTo(expected)`)
13- **Mockito** for mocking dependencies
14- **Testcontainers** for integration tests requiring databases or services
15 
16## Test Organization
17 
18```
19src/test/java/com/example/app/
20  service/           # Unit tests for service layer
21  controller/        # Web layer / API tests
22  repository/        # Data access tests
23  integration/       # Cross-layer integration tests
24```
25 
26Mirror the `src/main/java` package structure in `src/test/java`.
27 
28## Unit Test Pattern
29 
30```java
31@ExtendWith(MockitoExtension.class)
32class OrderServiceTest {
33 
34    @Mock
35    private OrderRepository orderRepository;
36 
37    private OrderService orderService;
38 
39    @BeforeEach
40    void setUp() {
41        orderService = new OrderService(orderRepository);
42    }
43 
44    @Test
45    @DisplayName("findById returns order when exists")
46    void findById_existingOrder_returnsOrder() {
47        var order = new Order(1L, "Alice", BigDecimal.TEN);
48        when(orderRepository.findById(1L)).thenReturn(Optional.of(order));
49 
50        var result = orderService.findById(1L);
51 
52        assertThat(result.customerName()).isEqualTo("Alice");
53        verify(orderRepository).findById(1L);
54    }
55 
56    @Test
57    @DisplayName("findById throws when order not found")
58    void findById_missingOrder_throws() {
59        when(orderRepository.findById(99L)).thenReturn(Optional.empty());
60 
61        assertThatThrownBy(() -> orderService.findById(99L))
62            .isInstanceOf(OrderNotFoundException.class)
63            .hasMessageContaining("99");
64    }
65}
66```
67 
68## Parameterized Tests
69 
70```java
71@ParameterizedTest
72@CsvSource({
73    "100.00, 10, 90.00",
74    "50.00, 0, 50.00",
75    "200.00, 25, 150.00"
76})
77@DisplayName("discount applied correctly")
78void applyDiscount(BigDecimal price, int pct, BigDecimal expected) {
79    assertThat(PricingUtils.discount(price, pct)).isEqualByComparingTo(expected);
80}
81```
82 
83## Integration Tests
84 
85Use Testcontainers for real database integration:
86 
87```java
88@Testcontainers
89class OrderRepositoryIT {
90 
91    @Container
92    static PostgreSQLContainer<?> postgres = new PostgreSQLContainer<>("postgres:16");
93 
94    private OrderRepository repository;
95 
96    @BeforeEach
97    void setUp() {
98        var dataSource = new PGSimpleDataSource();
99        dataSource.setUrl(postgres.getJdbcUrl());
100        dataSource.setUser(postgres.getUsername());
101        dataSource.setPassword(postgres.getPassword());
102        repository = new JdbcOrderRepository(dataSource);
103    }
104 
105    @Test
106    void save_and_findById() {
107        var saved = repository.save(new Order(null, "Bob", BigDecimal.ONE));
108        var found = repository.findById(saved.getId());
109        assertThat(found).isPresent();
110    }
111}
112```
113 
114For Spring Boot integration tests, see skill: `springboot-tdd`.
115 
116## Test Naming
117 
118Use descriptive names with `@DisplayName`:
119- `methodName_scenario_expectedBehavior()` for method names
120- `@DisplayName("human-readable description")` for reports
121 
122## Coverage
123 
124- Target 80%+ line coverage
125- Use JaCoCo for coverage reporting
126- Focus on service and domain logic — skip trivial getters/config classes
127 
128## References
129 
130See skill: `springboot-tdd` for Spring Boot TDD patterns with MockMvc and Testcontainers.
131See skill: `java-coding-standards` for testing expectations.
132