Pact contract tests: verify service messages without burning the house down

Pact tests HTTP and message integrations by asserting that inter-application messages conform to a shared understanding in a contract. Without contract testing, teams often rely on costly, brittle integration tests; Pact’s analogy is testing a smoke alarm with its button rather than setting the house on fire. Contract testing checks each application in isolation so sends and receives match the contract—HTTP request/response pairs or queue messages. A common Pact pattern is verifying that test doubles behave like the real collaborator. It applies wherever two services communicate, and scales especially well in microservice environments with many integrations.

API and platform teams can catch breaking request or payload changes in CI before deploy, instead of discovering them only in shared environments.

Contracts here are executable agreements about message shape and meaning—shared semantics between producers and consumers that stay testable as systems evolve.