Contract Testing

Contract testing verifies the agreement between a consumer and a provider, the consumer states the request and expected response shape and the provider is verified to always return it, catching boundary breakages without full end-to-end, using a tool like Pact with a Pact Broker.

In microservices, independently deployed services drift apart at their interfaces, so contract testing captures each consumer's expectations and verifies the provider against them in CI, catching breaking changes before deployment instead of in a production outage.