Tdd Red Green Refactor Agent Skill
> Enforces a disciplined Red-Green-Refactor (TDD) workflow in TypeScript/Node.js. Use this whenever creating new features, fixing bugs, or migrating logic to ensure high-quality, verifiable implementations.
Install
one command, takes just this skill from the repositorynpx skills add https://github.com/google-labs-code/design.md --skill tdd-red-green-refactorThe instruction itself
10 sections, as written by the authorRed-Green-Refactor (TDD) Skill: TypeScript Edition
This skill implements a structural framework for AI-assisted programming to ensure every line of code is verifiable, typed, and purposeful.
The Three-Phase Cycle
Phase 1: Red (Establish Failure)
You must prove the feature does not exist and that your test is valid.
- Write One Test: Create a single test case (e.g., in Vitest or Jest) for the next small piece of behavior.
- Execute & Fail: Run the test. It must fail.
- Verify: Ensure the failure is related to the missing logic (e.g.,
ReferenceError: add is not defined) and not a configuration error.
Phase 2: Green (Minimal Pass)
Make the test pass as quickly and simply as possible.
- Minimal Implementation: Write the simplest code that satisfies the test. Do not build for the future; focus strictly on the current "Red" test.
- Run Tests: Execute the suite. All tests must be Green.
- Evidence: The transition from Red to Green is the "Proof of Work" for the developer.
Phase 3: Refactor (Clean Up)
Improve the code structure while maintaining the "Green" state.
- Clean Up: Improve naming, remove duplication, and optimize the code written in Phase 2.
- Safety Net: Rerun the tests after every change. If they turn Red, revert the change immediately.
Core Operational Rules
1. No "Horizontal Splurging"
You are strictly forbidden from writing a large "splurge" of multiple tests at once. You must follow a strictly incremental loop:
- Write 1 Test -> See it Fail -> Write 1 Fix -> See it Pass.
- Repeat this loop for every sub-feature.
2. Impose Backpressure
Use automated assertions and strong typing (TypeScript) as backpressure to prevent the AI from "guessing" the solution or "playing in the mud" with low-quality code.
3. Verification of Integrity
Never modify an existing test to make a failing implementation pass. If a test must change, it must be because the requirement changed, not because the code is difficult to write.
Example Workflow (TypeScript + Vitest)
Step 1: Red
// math.test.ts
import { describe, it, expect } from 'vitest';
import { add } from './math';
describe('add', () => {
it('should sum two numbers', () => {
expect(add(2, 2)).toBe(4); // Fails: ReferenceError: add is not defined
});
});
Step 2: Green
// math.ts
export const add = (a: any, b: any) => {
return 4; // Passes: Minimal code to satisfy the test
};
Step 3: Refactor
// math.ts
/**
* Sums two numbers with explicit type safety.
*/
export const add = (a: number, b: number): number => {
return a + b; // Passes: Proper implementation with safety net
};
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How to use it
Take google-labs-code/tdd-red-green-refactor from the repository into ~/.claude/skills for personal
use, or into .claude/skills inside a project.
The agent identifies a skill by the name field in its header. Two skills with the
same name cannot sit side by side — one of them will be ignored.