Api Contract Testing

This handles contract testing between microservices so you catch breaking API changes before deployment. It covers Pact for consumer-driven contracts with proper matchers and provider verification, OpenAPI validation middleware, and shows both happy path and error scenarios. The TypeScript examples are solid and include state handlers for test setup. What's nice is the focus on structure over specific values, which is the whole point of contract testing. You'll want this when you have services talking to each other and need confidence that changes won't break consumers. The best practices section actually earns its keep by steering you away from common mistakes like testing business logic in contracts.