common-tdd
Implements a strict Red-Green-Refactor loop to ensure zero production code is written without a prior failing test. Use when: creating new features, fixing bugs, or expanding test coverage. (triggers: **/*.test.ts, **/*.spec.ts, **/*_test.go, **/*Test.java, **/*_test.dart, **/*_spec.rb, tdd, unit test, write test, red green refactor, failing test, test coverage)
Best use case
common-tdd is best used when you need a repeatable AI agent workflow instead of a one-off prompt.
Implements a strict Red-Green-Refactor loop to ensure zero production code is written without a prior failing test. Use when: creating new features, fixing bugs, or expanding test coverage. (triggers: **/*.test.ts, **/*.spec.ts, **/*_test.go, **/*Test.java, **/*_test.dart, **/*_spec.rb, tdd, unit test, write test, red green refactor, failing test, test coverage)
Teams using common-tdd should expect a more consistent output, faster repeated execution, less prompt rewriting.
When to use this skill
- You want a reusable workflow that can be run more than once with consistent structure.
When not to use this skill
- You only need a quick one-off answer and do not need a reusable workflow.
- You cannot install or maintain the underlying files, dependencies, or repository context.
Installation
Claude Code / Cursor / Codex
Manual Installation
- Download SKILL.md from GitHub
- Place it in
.claude/skills/common-tdd/SKILL.mdinside your project - Restart your AI agent — it will auto-discover the skill
How common-tdd Compares
| Feature / Agent | common-tdd | Standard Approach |
|---|---|---|
| Platform Support | Not specified | Limited / Varies |
| Context Awareness | High | Baseline |
| Installation Complexity | Unknown | N/A |
Frequently Asked Questions
What does this skill do?
Implements a strict Red-Green-Refactor loop to ensure zero production code is written without a prior failing test. Use when: creating new features, fixing bugs, or expanding test coverage. (triggers: **/*.test.ts, **/*.spec.ts, **/*_test.go, **/*Test.java, **/*_test.dart, **/*_spec.rb, tdd, unit test, write test, red green refactor, failing test, test coverage)
Where can I find the source code?
You can find the source code on GitHub using the link provided at the top of the page.
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SKILL.md Source
# Test-Driven Development (TDD) Standard ## **Priority: P0 — The Iron Law** > **NO PRODUCTION CODE WITHOUT A FAILING TEST FIRST.** > Code written before the test MUST be deleted. Start over. ## **Step 1: The RGR Loop (Red-Green-Refactor)** 1. **RED**: Write a minimal failing test. **Verify failure** (Expected error, not typo). 2. **GREEN**: Write simplest code to pass. **Verify pass**. 3. **REFACTOR**: Clean up code while staying green. ## **AAA Structure (Mandatory)** Every test must follow Arrange-Act-Assert: - **Arrange**: Set up inputs, stubs, mocks, and expected values. - **Act**: Call the single unit under test. - **Assert**: Verify output and side effects. One logical assertion per test. **(See [AAA Example](references/aaa_example.md) for code structure)**. ## **Step 3: Verification & Thresholds** - **Minimum Coverage**: 80% (Stat/Func/Line), 75% (Branch). - **Mocks**: - Always mock: HTTP, Time/Date, Filesystem. - Never mock: Fast internal services (<200ms), pure domain logic. - See [Test Runner Reference](references/test_runners.md) for environment-specific commands. ## **Step 4: Principles & Mocks** - **Watch it Fail**: Prove the test works before writing code. - **Minimalism**: Don't add features/options beyond current test (YAGNI). - **Isolation**: Mock external APIs (HTTP) and Time. - **Realism**: Prefer real DBs (test containers) and fast internal services (<200ms). ## **Verification Checklist** - [ ] Every new function/method has a failing test first? - [ ] Failure message was expected? - [ ] Minimal code implemented passed? - [ ] AAA structure followed? - [ ] Coverage thresholds met? ## **Expert References** - [AAA Example](references/aaa_example.md) - [AAA Methodology](references/aaa_methodology.md) - [Test Runners](references/test_runners.md) - [TDD Patterns](references/tdd_patterns.md) - [Testing Anti-Patterns](references/testing_anti_patterns.md) ## Anti-Patterns - **No test-after**: Writing tests post-implementation defeats TDD. Delete and restart. - **No assertion-free tests**: A test without an assert is not a test. - **No testing implementation**: Test behavior and contracts, not internal calls.
Related Skills
common-observability
Enforce structured JSON logging, OpenTelemetry distributed tracing, and RED metrics across backend services. Use when adding request correlation, setting up tracing spans, defining SLO burn-rate alerts, or instrumenting middleware. (triggers: **/*.service.ts, **/*.handler.ts, **/*.middleware.ts, **/*.interceptor.ts, **/*.go, **/*.java, **/*.kt, **/*.py, logging, tracing, metrics, opentelemetry, observability, slo)
common-mobile-ux-core
Enforce universal mobile UX principles for touch-first interfaces including touch targets, safe areas, and mobile-specific interaction patterns. Use when building mobile screens, handling touch interactions, or validating safe area compliance. (triggers: **/*_page.dart, **/*_screen.dart, **/*_view.dart, **/*.swift, **/*Activity.kt, **/*Screen.tsx, mobile, responsive, SafeArea, touch, gesture, viewport)
common-mobile-animation
Apply motion design principles for mobile apps covering timing curves, transitions, gestures, and performance-conscious animations. Use when implementing screen transitions, gesture-driven interactions, shared-element animations, or optimizing animation frame rates on iOS, Android, or Flutter. (triggers: **/*_page.dart, **/*_screen.dart, **/*.swift, **/*Activity.kt, **/*Screen.tsx, Animation, AnimationController, Animated, MotionLayout, transition, gesture)
common-error-handling
Cross-cutting standards for error design, response shapes, error codes, and boundary placement across API, domain, and infrastructure layers. Use when defining error hierarchies, wrapping exceptions, building standardized error responses, or placing error boundaries in layered architectures. (triggers: **/*.service.ts, **/*.handler.ts, **/*.controller.ts, **/*.go, **/*.java, **/*.kt, **/*.py, error handling, exception, try catch, error boundary, error response, error code, throw)
common-architecture-diagramming
Standards for creating clear, audience-appropriate C4 and UML architecture diagrams with Mermaid. Use when producing system context diagrams, container views, sequence diagrams, or updating ARCHITECTURE.md files. (triggers: ARCHITECTURE.md, **/*.mermaid, **/*.drawio, diagram, architecture, c4, system design, mermaid)
common-architecture-audit
Audit structural debt, logic leakage, and monolithic components across Web, Mobile, and Backend codebases. Use when reviewing architecture, assessing tech debt, detecting logic in wrong layers, or identifying God classes. (triggers: package.json, pubspec.yaml, go.mod, pom.xml, nest-cli.json, architecture audit, code review, tech debt, logic leakage, refactor)
common-api-design
Apply REST API conventions — HTTP semantics, status codes, versioning, pagination, and OpenAPI standards for any framework. Use when designing endpoints, choosing HTTP methods, implementing pagination, or writing OpenAPI specs. (triggers: **/*.controller.ts, **/*.router.ts, **/*.routes.ts, **/routes/**, **/controllers/**, **/handlers/**, rest api, endpoint, http method, status code, versioning, pagination, openapi, api design, api contract)
common-accessibility
Enforce WCAG 2.2 AA compliance with semantic HTML, ARIA roles, keyboard navigation, and color contrast standards for web UIs. Use when building interactive components, adding form labels, fixing focus traps, or auditing a11y compliance. (triggers: **/*.tsx, **/*.jsx, **/*.html, **/*.vue, **/*.component.html, accessibility, a11y, wcag, aria, screen reader, focus, alt text)
common-workflow-writing
Rules for writing concise, token-efficient workflow and skill files. Prevents over-building that requires costly optimization passes. Use when creating or editing workflow files, SKILL.md files, or new skill definitions. (triggers: .agent/workflows/*.md, SKILL.md, create workflow, write workflow, new skill, new workflow)
common-ui-design
Design distinctive, production-grade frontend UI with bold aesthetic choices. Use when building web components, pages, interfaces, dashboards, or applications in any framework (React, Next.js, Angular, Vue, HTML/CSS). (triggers: build a page, create a component, design a dashboard, landing page, UI for, build a layout, make it look good, improve the design, build UI, create interface, design screen)
common-system-design
Enforce separation of concerns, dependency inversion, and resilience patterns across layered and distributed architectures. Use when designing new features, evaluating module boundaries, selecting architectural patterns, or resolving scalability bottlenecks. (triggers: architecture, design, system, scalability, microservice, module boundary, coupling)
common-store-changelog
Generate user-facing release notes for the Apple App Store and Google Play Store by collecting git history, triaging user-impacting changes, and drafting store-compliant changelogs. Enforces character limits (App Store ≤4000, Google Play ≤500), tone, and bullet format. Use when generating release notes, app store changelog, play store release, what's new, or version release notes for any mobile app. (triggers: generate changelog, app store notes, play store release, what's new, release notes, version notes, store release)