Testing Pyramid

Structure

Unit Tests         — fast domain logic checks without a Spring context
Slice Tests        — focused web or persistence infrastructure checks
Integration Tests  — cross-boundary behavior with real dependencies

Unit Tests — Services

Choose the mix by risk, not a fixed percentage. Use real database/Redis tests for concurrency, serialization and transaction semantics that mocks cannot establish. Preserve the project's JUnit/AssertJ and mocking conventions; changing assertion libraries is not a correctness fix.

@ExtendWith(MockitoExtension.class)
class OrderServiceTest {