contract-testing

name	contract-testing
description	Consumer-driven contract testing for microservices using Pact, schema validation, API versioning, and backward compatibility testing. Use when testing API contracts or coordinating distributed teams.
category	testing-methodologies
priority	high
tokenEstimate	900
agents	["qe-api-contract-validator","qe-test-generator","qe-security-scanner"]
implementation_status	optimized
optimization_version	1
last_optimized	"2025-12-02T00:00:00.000Z"
dependencies	[]
quick_reference_card	true
tags	["contract","pact","consumer-driven","api","microservices","schema-validation"]
trust_tier	3
validation	{"schema_path":"schemas/output.json","validator_path":"scripts/validate-config.json","eval_path":"evals/contract-testing.yaml"}

Contract Testing

<default_to_action> When testing API contracts or microservices:

1. DEFINE consumer expectations (what consumers actually need)
2. VERIFY provider fulfills contracts (Pact verification)
3. DETECT breaking changes before deployment (CI/CD integration)
4. VERSION APIs semantically (breaking = major bump)
5. MAINTAIN backward compatibility for supported versions

Quick Contract Testing Steps:

• Consumer: Define expected request/response pairs
• Provider: Verify against all consumer contracts
• CI/CD: Block deploys that break contracts
• Versioning: Document supported versions and deprecation

Critical Success Factors:

• Consumers own the contract (they define what they need)
• Provider must pass all consumer contracts before deploy
• Breaking changes require coordination, not surprise </default_to_action>

Quick Reference Card

When to Use

• Microservices communication
• Third-party API integrations
• Distributed team coordination
• Preventing breaking changes

Consumer-Driven Contract Flow

Consumer → Defines Expectations → Contract
                    ↓
Provider → Verifies Contract → Pass/Fail
                    ↓
CI/CD → Blocks Breaking Changes

Breaking vs Non-Breaking Changes

Change Type	Breaking?	Semver
Remove field	✅ Yes	Major
Rename field	✅ Yes	Major
Change type	✅ Yes	Major
Add optional field	❌ No	Minor
Add new endpoint	❌ No	Minor
Bug fix	❌ No	Patch

Tools

Tool	Best For
Pact	Consumer-driven contracts
OpenAPI/Swagger	API-first design
JSON Schema	Schema validation