test(guest): add backend unit tests for guest checkout to fix CI
The guest checkout PR (#17) added new backend code without any unit
tests, causing the jacocoTestCoverageVerification CI step to fail
(coverage dropped below 70% line / 60% branch thresholds).
OrderServiceTest — 10 new tests covering:
- createGuestOrder: correct fields, plate normalization, email
normalization (lowercase+trim), null email handling
- getOrderByGuestToken: successful lookup, not-found, security check
(refuses to serve user-owned orders via guest token)
- confirmGuestPayment: success path (status→PROCESSING, notification),
non-pending order throws, unknown token throws
GuestOrderControllerTest — new file, 8 tests covering:
- POST /api/guest-orders: create without auth (201), validation
(bad plate, blank email, invalid email, blank letter text)
- GET /api/guest-orders/{token}: lookup (200), not-found (404)
- POST /api/guest-orders/{token}/pay: confirm (200), conflict (409),
not-found (404)
All tests follow existing patterns (MockitoExtension for service,
SpringBootTest+MockMvc for controller). Cannot run backend tests
locally (no JDK in agent sandbox) — CI will verify.
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