Api contract testing

Skill ulpi-io/plugin-marketplace/plugins/aj-geddes/skills/api-contract-testing

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Install

npx -y skills add ulpi-io/plugin-marketplace --skill api-contract-testing

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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.

SKILL.md

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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:

// 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	Pact for Consumer-Driven Contracts
OpenAPI Schema Validation	OpenAPI Schema Validation
JSON Schema Validation	JSON Schema Validation
REST Assured for Java	REST Assured for Java
Contract Testing with Postman	Contract Testing with Postman
Pact Broker Integration	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