name: test-first
description: Test-Driven Development (TDD Red-Green-Refactor)
user-invocable: true

Test-Driven Development

Implement TDD for: $ARGUMENTS

Quick Steps

1. Write a failing test
2. Run test, confirm failure
3. Write minimal code to pass
4. Refactor while keeping tests green
5. Repeat

Red Phase - Write Failing Test

Test Design Principles

• Test one specific behavior
• Test name describes expected result
• Test should fail (feature doesn't exist yet)

Must Test

• [ ] Normal case
• [ ] Edge cases
• [ ] Error cases
• [ ] Invalid input

Example

// auth/login.test.ts
it('should return JWT token for valid credentials', async () => {
  const res = await request(app)
    .post('/auth/login')
    .send({ email: '[email protected]', password: 'password123' })

  expect(res.status).toBe(200)
  expect(res.body.token).toBeDefined()
})

Green Phase - Minimal Implementation

Implementation Principles

• Write ONLY enough code to pass the test
• Don't optimize yet
• Don't worry about elegance
• Just make it work

Refactor Phase - Clean Up

Refactoring Checklist

• [ ] Is there code duplication?
• [ ] Are variable names clear?
• [ ] Are functions too long?
• [ ] Is the logic too complex?

Refactoring Rules

• Keep tests passing
• Change one thing at a time
• Run tests frequently

Test Quality Checklist

• [ ] Unit tests cover core logic
• [ ] Integration tests cover interactions
• [ ] Test names clearly describe intent
• [ ] Tests are independent and repeatable
• [ ] Tests run fast (unit tests < 100ms)
• [ ] Edge cases are covered

Follow TDD strictly. No shortcuts.