Testing Strategies

Testing Pyramid

     /\        E2E (few) - Critical user flows
    /  \
   /----\      Integration (some) - API, DB
  /      \
 /--------\    Unit (many) - Functions, classes

Unit Test Patterns

AAA Pattern

test('should calculate discount', () => {
  // Arrange
  const price = 100;
  const discount = 0.2;

  // Act
  const result = calculateDiscount(price, discount);

  // Assert
  expect(result).toBe(80);
});

Test Doubles

// Mock - Verify interactions
const mockSave = jest.fn();

// Stub - Provide canned responses
jest.spyOn(api, 'fetch').mockResolvedValue({ data: [] });

// Fake - Working implementation
const fakeDb = new InMemoryDatabase();

What to Test

DO Test

• Business logic
• Edge cases (null, empty, max values)
• Error handling
• Public API contracts

DON'T Test

• Implementation details
• Third-party libraries
• Simple getters/setters
• Framework code

Coverage Goals

• Unit: 80%+
• Integration: Critical paths
• E2E: Happy paths + main flows

Test Naming

should [expected behavior] when [condition]

Example: should return null when user not found