Feature/integration tests

[soraiayugulis]

Summary

Adds comprehensive integration and end-to-end tests covering the full authorization pipeline, concurrent transaction handling, and all REST API endpoints via Spring context.

Changes

E2E Tests

• AuthorizationFlowE2ETest — complete flow: register card → add balance → register merchant → authorize
  • Successful authorization with balance deduction
  • MEAL → FOOD fallback end-to-end
  • Denial flow with INSUFFICIENT_BALANCE
  • Daily limit enforcement across multiple transactions

Concurrent Tests

• ConcurrentTransactionE2ETest — 10-thread concurrent authorization
  • Verifies no balance inconsistencies after concurrent transactions
  • Confirms sequential processing per card (5 threads, all approved)

API Integration Tests

• ApiIntegrationTest — @SpringBootTest with @AutoConfigureMockMvc
  • Tests all 8 endpoints in order via real HTTP calls
  • Verifies request/response serialization
  • Covers: POST /cards, POST /balance, GET /balance, POST /merchants, POST /transactions, GET /transactions, PUT /status, GET /cards/{id}

Configuration

• AppConfig — Spring @Configuration wiring all repositories, validators, checkers, and services as beans

Tests

• 114 total tests — all passing
• 30 domain unit tests
• 35 authorization service tests
• 15 repository tests
• 24 controller tests
• 4 fraud detection tests
• 4 E2E flow tests
• 2 concurrent tests
• 8 API integration tests

Success Criteria ✅

• All domain models with proper validation
• Authorization service with MEAL fallback
• Daily transaction limit enforced
• All REST API endpoints functional
• Fraud detection decoupled and functional
• All unit tests pass
• All integration tests pass
• All end-to-end tests pass
• Hexagonal architecture maintained