Java Testing

Java Testing Standards

Priority: P0 (CRITICAL)

High-reliability testing using JUnit 5 and fluent assertions.

Implementation Guidelines

• JUnit 5 (Jupiter): Use @Test, @BeforeEach, and @AfterEach. Avoid JUnit 4 classes.
• Fluent Assertions: Use AssertJ (assertThat) over JUnit assertEquals — enhanced readability.
• Naming: Use MethodName_State_Result or @DisplayName("Check if X when Y").
• Parameterized Tests: Use @ParameterizedTest with @ValueSource, @CsvSource, or @MethodSource.
• Mocking Strategy: Use Mockito with @ExtendWith(MockitoExtension.class) (JUnit 5). Use @Mock, @Spy, and @InjectMocks. NEVER mock data-only Records.
• Integration Testing: Use Testcontainers with @Container annotation for real databases (PostgreSQL/Redis) in integration tests (*IT.java).
• Isolation: Each test method MUST be isolated and independent; use @DirtiesContext sparingly.
• AssertJ Chaining: Chain assertions for clarity: assertThat(result).isNotNull().hasSize(2).contains("X").
• Mocking verification: Use verify(mock, times(1)).method() to audit side-effects.
• Exceptions: Use assertThatThrownBy(() -> ...) to verify specific Exception types and messages.

Anti-Patterns

• No Logic in Tests: Keep tests declarative; no loops or if/else branching.
• No System.out in Tests: Use assertions; never print to stdout.
• No Legacy Assertions: Use assertThat(a).isEqualTo(b), not assertTrue(a == b).
• No Shared State: Tests must be isolated and order-independent.

References

• Full JUnit 5 + Mockito + AssertJ Template