red-green-refactor

name	red-green-refactor
description	Guides the red-green-refactor TDD workflow: write a failing test first, implement the minimum code to make it pass, then refactor while keeping tests green. Use when a user asks to practice TDD, write tests first, follow red-green-refactor, do test-driven development, write failing tests before code, or phrases like 'make the test pass', 'test coverage', or 'unit tests before implementation'.
version	1.0.0
triggers	["tdd","test driven","write tests first","red green refactor","failing test"]
tags	["tdd","testing","quality","methodology"]
difficulty	intermediate
estimatedTime	15
relatedSkills	["testing/test-patterns","testing/anti-patterns"]

Red-Green-Refactor Methodology

You are following the RED-GREEN-REFACTOR cycle for test-driven development. Every new feature, bug fix, or behavior change starts with a failing test.

The Cycle

1. RED Phase — Write a Failing Test

1. Understand the requirement — what specific behavior must exist?
2. Write one test asserting that behavior
3. Run the test — it MUST fail (red)
4. Verify the failure reason — not a syntax error, but a missing implementation

The test should be focused on ONE behavior, named descriptively, and use clear assertions.

Executable example (Jest):

// calculateTotal.test.js
const { calculateTotal } = require('./calculateTotal');

describe('calculateTotal', () => {
  it('should apply 10% discount when total exceeds 100', () => {
    const items = [{ price: 60 }, { price: 60 }]; // total = 120
    expect(calculateTotal(items)).toBe(108); // 120 * 0.90
  });
});

Running this now produces: Cannot find module './calculateTotal' — correct RED state.

---

2. GREEN Phase — Make the Test Pass

Write the minimum code needed to pass the test. Don't add anything extra.

// calculateTotal.js
function calculateTotal(items) {
  const total = items.reduce((sum, item) => sum + item., );
   total >  ? total *  : total;
}
. = { calculateTotal };