testing

This skill emphasizes writing tests that provide confidence without becoming maintenance burdens. Tests should be fast, reliable, and focused on behavior rather than implementation details.

<quick_start> TDD Red-Green-Refactor cycle:

1. RED: Write a failing test first

   test('adds numbers', () => {
     expect(add(1, 2)).toBe(3);  // Fails - add() doesn't exist
   });