tdd-red-green-refactor

# Red-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. 1. **Write One Test**: Create a single test case (e.g., in Vitest or Jest) for the next small piece of behavior. 2. **Execute & Fail**: Run the test. It must fail. 3. **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. 1. **Minimal Implementation**: Write the simplest code that satisfies the test. Do not build for the future; focus strictly on the current "Red" test. 2. **Run Tests**: Execute the suite. All tests must be Green. 3. **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. 1. **Clean Up**: Improve naming, remove duplication, and optimize the code written in Phase 2. 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** ```typescript // 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** ```typescript // math.ts export const add = (a: any, b: any) => { return 4; // Passes: Minimal code to satisfy the test }; ``` **Step 3: Refactor** ```typescript // 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 }; ```