Test-Driven Development (TDD)

When to use this skill

• Starting a new complex feature.
• Fixing a bug (write test to reproduce first).
• Refactoring critical paths.

1. The Cycle (Red-Green-Refactor)

1. Red: Write a failing test that defines the desired behavior.
2. Green: Write the minimum code to pass the test.
3. Refactor: Clean up the code while keeping tests green.

2. Tools & Config

• PHP: Use Pest or PHPUnit.
  • php artisan test (Laravel).
• JS/TS: Use Jest or Vitest.
  • npm test.

3. Best Practices

• Arrangement: Arrange-Act-Assert structure in every test.
• Naming: it_should_validate_email or test_email_validation.
• Speed: Unit tests must run in milliseconds. Mock external services (Stripe, DB) if they are slow.