Contract tests validate that each service’s outputs conform to the expectations of its consumers. As described above, consumer-driven contract testing (Pact) and statistical contract testing (Great Expectations) detect silent breaking changes that integration testing may miss.

In the CI/CD pipeline, contract tests run for every service change. A contract test failure blocks deployment. The tests validate data schemas (types, field names, required fields), value ranges and distributions (statistical contract testing), response latency and throughput, error handling and fallback behaviour, and format compliance for any regulatory data flows such as logging output destined for the audit layer.

The contract test suite is version-controlled alongside the services and referenced in the AISDP as part of the quality management documentation. For microservice architectures, contract tests are the primary mechanism for ensuring that changes to one service do not silently degrade the behaviour of dependent services. The test results are retained as Module 5 evidence, and any contract violations are logged with the resolution actions taken.

Key outputs

• Consumer-driven contracts (Pact) per service interface
• Statistical contracts (Great Expectations) per data interface
• CI pipeline integration with deployment blocking on failure
• Module 5 AISDP evidence