testing-strategieslisted

# Testing Strategies ## When to use this skill - **New project**: define a testing strategy - **Quality issues**: bugs happen frequently - **Before refactoring**: build a safety net - **CI/CD setup**: automated tests ## Instructions ### Step 1: Understand the Test Pyramid ``` /\ /E2E\ ← few (slow, expensive) /______\ / \ /Integration\ ← medium /____________\ / \ / Unit Tests \ ← many (fast, inexpensive) /________________\ ``` **Ratio guide**: - Unit: 70% - Integration: 20% - E2E: 10% ### Step 2: Unit testing strategy **Given-When-Then pattern**: ```typescript describe('calculateDiscount', () => { it('should apply 10% discount for orders over $100', () => { // Given: setup const order = { total: 150, customerId: '123' }; // When: perform action const discount = calculateDiscount(order); // Then: verify result expect(discount).toBe(15); }); it('should not apply discount for orders under $100', () => { const order = { total: 50, customerId: '123' }; const discount = calculateDiscount(order); expect(discount).toBe(0); }); it('should throw error for invalid order', () => { const order = { total: -10, customerId: '123' }; expect(() => calculateDiscount(order)).toThrow('Invalid order'); }); }); ``` **Mocking strategy**: ```typescript // Mock external dependencies jest.mock('../services/emailService'); import { sendEmail } from '../services/emailServi