Contract Test Design

When to Use This Skill

Use this skill when:

• Contract Test Design tasks - Working on consumer-driven contract testing strategies using Pact
• Planning or design - Need guidance on contract testing approaches
• Best practices - Want to follow established patterns and standards

Overview

Contract testing verifies that services communicate correctly by testing the contract (API agreement) between a consumer and provider. Consumer-driven contracts (CDC) ensure providers don't break their consumers.

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Contract Testing vs Other Test Types

Aspect	E2E Tests	Integration Tests	Contract Tests
Scope	Full system	Component + deps	Consumer-provider
Speed	Slow (minutes)	Medium (seconds)	Fast (ms)
Reliability	Often flaky	Moderate	Very stable
Deployment coupling	High	Medium	Low (async)
Failure localization	Poor	Moderate	Excellent
Maintenance	High	Medium	Low

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Consumer-Driven Contract Flow

┌─────────────────────────────────────────────────────────────┐
│                    CONSUMER SIDE                            │
│                                                             │
│  1. Consumer writes test   2. Test generates contract       │
│     ┌──────────────┐          ┌──────────────┐              │
│     │ Consumer     │          │   Contract   │              │
│     │ Test         │  ─────►  │   (JSON)     │              │
│     └──────────────┘          └──────────────┘              │
│                                      │                      │
└──────────────────────────────────────┼──────────────────────┘
                                       │
                                       ▼ Publish to Broker
                              ┌──────────────────┐
                              │  Contract Broker │
                              │  (Pact Broker)   │
                              └────────┬─────────┘
                                       │
┌──────────────────────────────────────┼──────────────────────┐
│                    PROVIDER SIDE     │                      │
│                                      ▼                      │
│  3. Provider verifies contract                              │
│     ┌──────────────┐          ┌──────────────┐              │
│     │  Provider    │  ◄─────  │   Contract   │              │
│     │  Verification│          │   (JSON)     │              │
│     └──────────────┘          └──────────────┘              │
│            │                                                │
│            ▼                                                │
│  4. Provider tests pass = Contract honored                  │
│                                                             │
└─────────────────────────────────────────────────────────────┘

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Quick Reference: Breaking Changes

Change Type	Breaking?	Action
Remove field	Yes	Block deployment
Change field type	Yes	Block deployment
Add required field	Yes	Block deployment
Add optional field	No	Allow
Add new endpoint	No	Allow

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Tooling Selection

Purpose	Tool	Rationale
Contract Framework	PactNet	.NET native, mature
Broker	Pact Broker	Standard, free tier
Async Contracts	Pact Message	Same ecosystem
Schema Validation	OpenAPI	Industry standard

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References

Reference	Content	When to Load
strategy-template.md	Contract testing strategy template, service maps, workflows	Planning contract testing strategy
pact-dotnet-implementation.md	Consumer tests, provider verification, provider states	Implementing Pact in .NET
message-contracts.md	Async message/event contract testing	Testing event-driven architectures
matchers-cicd.md	Pact matchers, breaking change detection, CI/CD pipelines	Matcher syntax, CI/CD integration

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Integration Points

Inputs from:

• API specifications → Contract definitions
• Service architecture → Consumer-provider map

• test-strategy-planning

  skill → Contract test scope

Outputs to:

• CI/CD pipeline → Contract verification gates
• API governance → Breaking change detection

• api-design-fundamentals

  skill → Contract-first design

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Test Scenarios

Scenario 1: Planning contract testing strategy

Query: "Help me design a contract testing strategy for our microservices"

Expected: Skill activates, provides strategy template, guides through service mapping

Scenario 2: Implementing Pact tests

Query: "Show me how to write Pact consumer tests in .NET"

Expected: Skill activates, loads pact-dotnet-implementation.md reference, provides code examples

Scenario 3: CI/CD integration

Query: "How do I integrate contract testing into our GitHub Actions pipeline?"

Expected: Skill activates, loads matchers-cicd.md reference, provides pipeline examples

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Last Updated: 2025-12-28

Version History

• v1.1.0 (2025-12-28): Refactored to progressive disclosure - extracted implementation to references/
• v1.0.0 (2025-12-26): Initial release