Integration Test Plan & QA Coverage Matrix

# Integration Test Plan & QA Coverage Matrix

## 1. Testing Pyramid & Target Budgets
- **Unit Tests (80%+ Branch Coverage):** Pure business logic, invariant rules, and domain entity methods. Execution time budget: < 30 seconds.
- **Integration Tests (95%+ API Contract Coverage):** Database repositories, caching layers, message broker outbox publishers, and third-party API adapters. Execution time budget: < 3 minutes.
- **End-to-End Tests (Critical User Journeys):** Browser-driven Playwright flows covering onboarding, authentication, checkout, and export.

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## 2. Service Boundary Testing Matrix

| Component Boundary | Test Strategy | Tooling / Harness | Gate Requirement |
| :--- | :--- | :--- | :--- |
| **HTTP / gRPC APIs** | Contract-First Testing | OpenAPI Spec + Prism Mocks | 100% schema conformance |
| **PostgreSQL Persistence** | Hermetic Testcontainers | Docker Compose + Testcontainers | Zero migration divergence |
| **Kafka Event Pipeline** | Embedded Broker Harness | EmbeddedKafka / Redpanda | Idempotent consumer replay |
| **Third-Party Gateways** | Deterministic HTTP Mocking | Mock Service Worker (MSW) | Network timeout & retry test |

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## 3. Failure Mode & Chaos Injection Tests
- [ ] Database connection pool exhaustion test (simulate 500 concurrent connections).
- [ ] Redis cache failure fallback test (ensure system gracefully falls back to database with rate limiting).
- [ ] Asynchronous webhook retry backoff validation (exponential backoff with jitter).