Contract tests assert that inter-application messages conform to a shared understanding that is documented and verifiable. By testing against this shared understanding (a contract), it is possible to validate the compatibility of inter-connected systems before they are ever deployed to an integrated environment. This helps to enable more consistent stability of the integrated environments, and helps reduce the impact to other teams that are dependent on integrated environments, by enabling developers to detect breaking changes while working on their local machines and as an automated quality gate before deploying any changes.
