---
name: api-contract-testing-d12944381add
description: >
  Verify API contracts between services to ensure compatibility and prevent
  breaking changes. Use for contract testing, Pact, API contract validation,
  schema validation, and consumer-driven contracts.
---

# API Contract Testing

## Table of Contents

- [Overview](#overview)
- [When to Use](#when-to-use)
- [Quick Start](#quick-start)
- [Reference Guides](#reference-guides)
- [Best Practices](#best-practices)

## Overview

Contract testing verifies that APIs honor their contracts between consumers and providers. It ensures that service changes don't break dependent consumers without requiring full integration tests. Contract tests validate request/response formats, data types, and API behavior independently.

## When to Use

- Testing microservices communication
- Preventing breaking API changes
- Validating API versioning
- Testing consumer-provider contracts
- Ensuring backward compatibility
- Validating OpenAPI/Swagger specifications
- Testing third-party API integrations
- Catching contract violations in CI

## Quick Start

Minimal working example:

```typescript
// tests/pact/user-service.pact.test.ts
import { PactV3, MatchersV3 } from "@pact-foundation/pact";
import { UserService } from "../../src/services/UserService";

const { like, eachLike, iso8601DateTimeWithMillis } = MatchersV3;

const provider = new PactV3({
  consumer: "OrderService",
  provider: "UserService",
  port: 1234,
  dir: "./pacts",
});

describe("User Service Contract", () => {
  const userService = new UserService("http://localhost:1234");

  describe("GET /users/:id", () => {
    test("returns user when found", async () => {
      await provider
        .given("user with ID 123 exists")
        .uponReceiving("a request for user 123")
        .withRequest({
          method: "GET",
          path: "/users/123",
          headers: {
// ... (see reference guides for full implementation)
```

## Reference Guides

Detailed implementations in the `references/` directory:

| Guide | Contents |
|---|---|
| [Pact for Consumer-Driven Contracts](references/pact-for-consumer-driven-contracts.md) | Pact for Consumer-Driven Contracts |
| [OpenAPI Schema Validation](references/openapi-schema-validation.md) | OpenAPI Schema Validation |
| [JSON Schema Validation](references/json-schema-validation.md) | JSON Schema Validation |
| [REST Assured for Java](references/rest-assured-for-java.md) | REST Assured for Java |
| [Contract Testing with Postman](references/contract-testing-with-postman.md) | Contract Testing with Postman |
| [Pact Broker Integration](references/pact-broker-integration.md) | Pact Broker Integration |

## Best Practices

### ✅ DO

- Test contracts from consumer perspective
- Use matchers for flexible matching
- Validate schema structure, not specific values
- Version your contracts
- Test error responses
- Use Pact broker for contract sharing
- Run contract tests in CI
- Test backward compatibility

### ❌ DON'T

- Test business logic in contract tests
- Hard-code specific values in contracts
- Skip error scenarios
- Test UI in contract tests
- Ignore contract versioning
- Deploy without contract verification
- Test implementation details
- Mock contract tests


---
Source attribution: aj-geddes
Original project: https://github.com/aj-geddes/useful-ai-prompts/blob/3f5182cfd739fc113f4af5244a1cf342ad7f7911/skills/api-contract-testing/SKILL.md
License: MIT
License information: https://opensource.org/license/mit
Original upstream instructions; downloaded from Mega AI Hub.

## Upstream license notice

MIT License

Copyright (c) 2025 AJ Geddes

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.


# Mega AI Hub resource metadata

Creator / publisher: aj-geddes
Original project: https://github.com/aj-geddes/useful-ai-prompts/blob/3f5182cfd739fc113f4af5244a1cf342ad7f7911/skills/api-contract-testing/SKILL.md
Attribution basis: Source repository record

Fields of work: Development & Engineering, Product Management
Roles: Backend Developer, Data Engineer, DevOps / SRE, QA / Test Engineer, Technical Product Manager
Specialties: API, Testing
Tools: Pact, Postman
Country applicability: Country not specified
Classification basis: Source catalog labels
Instruction SHA-256: 4cbe578c4c5511525871868b2512460a528678358d5ee450f780db8bfac6d535