/test-first

name: test-first
description: Drive one feature through a strict TDD Red-Green-Refactor cycle with checklists for each phase. Use when implementing new functionality test-first, or when the user runs /test-first.
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: 'test@example.com', 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**

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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**

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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

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Follow TDD strictly. No shortcuts.