test-first

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

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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()
})

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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.