contract-testing-builder

Use PactV3 from @pact-foundation/pact to define consumer interactions with given states, requests, and expected responses, then execute tests against the mock server. On the provider side, use the Verifier class with stateHandlers to seed test data and verify published pacts.

Consumer-driven contract testing lets API consumers define the exact requests and responses they depend on, which providers must then satisfy. This catches breaking changes early, enables independent development, and avoids needing a shared integration environment.

Pact captures actual consumer expectations as executable contracts verified against the provider, while OpenAPI validates requests and responses against a static specification using middleware like express-openapi-validator. Pact suits consumer-driven workflows; OpenAPI suits spec-first documentation and validation.

Run the Pact Verifier against your live provider with providerBaseUrl pointing to the running app, pactUrls or a broker for contracts, and stateHandlers that seed or clean database records for each provider state before verification.

Breaking changes include removing required response fields, changing field types, and removing enum values. Adding optional fields is safe, and deprecations should follow a documented notice period such as six months.

Run consumer pact tests on every push, publish generated pact files to a Pact Broker tagged with the commit SHA, then trigger provider verification jobs that fetch contracts from the broker using broker URL and token secrets.