contract-testing

# Contract Testing <default_to_action> When testing API contracts or microservices: 1. DEFINE consumer expectations (what consumers actually need) 2. VERIFY provider fulfills contracts (Pact verification) 3. DETECT breaking changes before deployment (CI/CD integration) 4. VERSION APIs semantically (breaking = major bump) 5. MAINTAIN backward compatibility for supported versions **Quick Contract Testing Steps:** - Consumer: Define expected request/response pairs - Provider: Verify against all consumer contracts - CI/CD: Block deploys that break contracts - Versioning: Document supported versions and deprecation **Critical Success Factors:** - Consumers own the contract (they define what they need) - Provider must pass all consumer contracts before deploy - Breaking changes require coordination, not surprise </default_to_action> ## Quick Reference Card ### When to Use - Microservices communication - Third-party API integrations - Distributed team coordination - Preventing breaking changes ### Consumer-Driven Contract Flow ``` Consumer → Defines Expectations → Contract ↓ Provider → Verifies Contract → Pass/Fail ↓ CI/CD → Blocks Breaking Changes ``` ### Breaking vs Non-Breaking Changes | Change Type | Breaking? | Semver | |-------------|-----------|--------| | Remove field | ✅ Yes | Major | | Rename field | ✅ Yes | Major | | Change type | ✅ Yes | Major | | Add optional field | ❌ No | Minor | | Add new endpoint | ❌ No | Minor | | Bug fix | ❌ No | Patch | ### Tools | Tool | Best For | |------|----------| | **Pact** | Consumer-driven contracts | | **OpenAPI/Swagger** | API-first design | | **JSON Schema** | Schema validation | | **GraphQL** | Schema-first contracts | --- ## Consumer Contract (Pact) ```javascript // Consumer defines what it needs const { Pact } = require('@pact-foundation/pact'); describe('Order API Consumer', () => { const provider = new Pact({ consumer: 'CheckoutUI', provider: 'OrderService' }); beforeAll(() => provider.setup()); afterAll(() => provider.finalize()); it('creates an order', async () => { await provider.addInteraction({ state: 'products exist', uponReceiving: 'a create order request', withRequest: { method: 'POST', path: '/orders', body: { productId: 'abc', quantity: 2 } }, willRespondWith: { status: 201, body: { orderId: like('order-123'), // Any string matching pattern total: like(19.99) // Any number } } }); const response = await orderClient.create({ productId: 'abc', quantity: 2 }); expect(response.orderId).toBeDefined(); }); }); ``` --- ## Provider Verification ```javascript // Provider verifies it fulfills all consumer contracts const { Verifier } = require('@pact-foundation/pact'); describe('Order Service Provider', () => { it('fulfills all consumer contracts', async () => { await new Verifier({ provider: 'OrderService', providerBaseUrl: 'http://localhost:3000', pactUrls: ['./pacts/checkoutui-orderservice.json'], stateHandlers: { 'products exist': async () => { await db.products.create({ id: 'abc', price: 9.99 }); } } }).verifyProvider(); }); }); ``` --- ## Breaking Change Detection ```typescript // Agent detects breaking changes await Task("Contract Validation", { currentContract: 'openapi-v2.yaml', previousContract: 'openapi-v1.yaml', detectBreaking: true, calculateSemver: true, generateMigrationGuide: true }, "qe-api-contract-validator"); // Output: // Breaking changes found: 2 // - Removed field: order.discount // - Type change: order.total (number → string) // Recommended version: 3.0.0 (major bump) ``` --- ## CI/CD Integration ```yaml name: Contract Tests on: [push] jobs: consumer-tests: steps: - run: npm run test:contract - name: Publish Pacts run: npx pact-broker publish ./pacts --broker-base-url $PACT_BROKER provider-verification: needs: consumer-tests steps: - name: Verify Provider run: npm run verify:contracts - name: Can I Deploy? run: npx pact-broker can-i-deploy --pacticipant OrderService --version $VERSION ``` --- ## Agent Coordination Hints ### Memory Namespace ``` aqe/contract-testing/ ├── contracts/* - Current contracts ├── breaking-changes/* - Detected breaking changes ├── versioning/* - Version compatibility matrix └── verification-results/* - Provider verification history ``` ### Fleet Coordination ```typescript const contractFleet = await FleetManager.coordinate({ strategy: 'contract-testing', agents: [ 'qe-api-contract-validator', // Validation, breaking detection 'qe-test-generator', // Generate contract tests 'qe-security-scanner' // API security ], topology: 'sequential' }); ``` --- ## Related Skills - [api-testing-patterns](../api-testing-patterns/) - API testing strategies - [shift-left-testing](../shift-left-testing/) - Early contract validation - [cicd-pipeline-qe-orchestrator](../cicd-pipeline-qe-orchestrator/) - Pipeline integration --- ## Remember **Consumers own the contract.** They define what they need; providers must fulfill it. Breaking changes require major version bumps and coordination. CI/CD blocks deploys that break contracts. Use Pact for consumer-driven, OpenAPI for API-first. **With Agents:** Agents validate contracts, detect breaking changes with semver recommendations, and generate migration guides. Use agents to maintain contract compliance at scale.