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Contract Testing

Testing & Quality
contract-testing

Contract Testing is an Agent Skill for testing & quality published in the thedaviddias/Front-End-Checklist repository on GitHub: a SKILL.md instruction file an AI agent can load to do this task.

Use when setting up integration testing for a frontend-backend API boundary, evaluating whether two services are safe to deploy independently, or replacing slow end-to-end tests with contract tests.

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How to use this skill

Bring this guide into your coding agent with a prompt tailored to the tool you use.

  1. Open your project in Codex.
  2. Copy and paste the prompt below.
  3. Review files and risks before approving any action.
Prompt to paste
Inspect the Agent Skill at https://github.com/thedaviddias/Front-End-Checklist/blob/HEAD/skills/contract-testing/SKILL.md and all supporting files. Report provenance, permissions, scripts, dependencies, and security risks. Propose an exact installation into .agents/skills/contract-testing, but wait for my approval before writing files or running scripts.

Copying this prompt does not install or run the skill. Review third-party files before use.

Implement consumer-driven contract testing for API boundaries

Integration tests that require both services running at the same time are slow, brittle, and hard to maintain. Consumer-driven contract testing decouples the consumer and provider test suites — each team can run their tests independently, yet the broker guarantees that the published contract is always verified against the live provider. This catches API mismatches days earlier than end-to-end tests, with far less infrastructure overhead.

Quick Reference

  • The consumer writes tests that describe what it expects from the API (the "contract")
  • The contract is published to a Pact Broker and verified against the real provider
  • Provider changes that break the contract fail CI before they are deployed
  • This replaces fragile end-to-end tests that require both services to be running simultaneously

Check

Check whether the frontend has consumer-driven contract tests that define and verify the API contract with the backend.

Fix

Add Pact consumer tests for the frontend API client, publish the contracts to a broker, and add provider verification to the backend CI pipeline.

Explain

Explain how consumer-driven contract testing works, what the Pact workflow looks like end-to-end, and how it compares to mocking and end-to-end testing.

Code Review

Review the Pact consumer tests. Flag interactions that are too permissive (any-type matchers on fields the consumer actually uses), missing status code assertions, and interactions for endpoints the consumer no longer calls.

For full implementation details, code examples, and framework-specific guidance, see references/rule.md.

Rule page: https://frontendchecklist.io/en/rules/testing/contract-testing