Writing Automated Tests

JavaScript
// Start with high-value integration tests
describe('User Registration Flow', () => {
  it('creates account and sends welcome email', async () => {
    const userData = { email: 'test@example.com', password: 'secure123' };
    
    const response = await request(app)
      .post('/register')
      .send(userData)
      .expect(201);
    
    expect(response.body.user.email).toBe(userData.email);
    expect(mockEmailService.sendWelcome).toHaveBeenCalledWith(userData.email);
  });
});

Testing Strategy:

1. Start with static analysis - Set up TypeScript/ESLint first for immediate confidence
2. Write integration tests - Cover critical user flows end-to-end
3. Add unit tests - Focus on complex business logic and edge cases
4. Monitor confidence levels - Ask "Would I deploy with confidence after these pass?"

Progress checklist for new projects:

• Configure TypeScript + ESLint
• Set up testing framework (Jest/Vitest)
• Write 3-5 integration tests for core flows
• Add unit tests for business logic
• Set up CI to run tests on every commit

Example 1: High-Confidence Integration Test Input: E-commerce checkout flow Output:

JavaScript
it('completes purchase with payment processing', async () => {
  const order = await createTestOrder();
  const paymentData = { cardToken: 'tok_visa', amount: 2999 };
  
  const result = await checkoutService.processPurchase(order.id, paymentData);
  
  expect(result.status).toBe('completed');
  expect(mockPaymentGateway.charge).toHaveBeenCalledWith(paymentData);
  expect(mockInventory.reserve).toHaveBeenCalledWith(order.items);
});

Example 2: Business Logic Unit Test Input: Tax calculation with multiple rules Output:

JavaScript
describe('TaxCalculator', () => {
  it('applies state tax and handles tax-exempt items', () => {
    const items = [
      { price: 100, taxable: true },
      { price: 50, taxable: false } // prescription medicine
    ];
    
    const tax = calculator.calculate(items, { state: 'CA', rate: 0.08 });
    
    expect(tax).toBe(8.00); // Only $100 taxed at 8%
  });
});

Maximize Confidence:

• Test the happy path AND edge cases that matter to users
• Integration tests for workflows, unit tests for algorithms
• Use TypeScript to catch type errors before runtime
• Mock external services but test integration points

Minimize Maintenance:

• Test behavior, not implementation details
• Use descriptive test names that explain the scenario
• Group related tests logically
• Keep setup/teardown simple and reusable

Practical Guidelines:

• If changing code requires updating 10+ tests, you're testing implementation
• If tests pass but the feature is broken, add integration coverage
• If you're afraid to refactor because tests might break, improve test design

Over-testing implementation:

JavaScript
// BAD - Tests internal method calls
expect(userService.validateEmail).toHaveBeenCalled();

// GOOD - Tests the outcome
expect(result.errors).toContain('Invalid email format');

Under-testing critical paths:

• Don't skip authentication, payment, or data persistence flows
• These bugs wake you up at 2 AM - test them thoroughly

False confidence from poor tests:

• Tests that always pass regardless of code changes
• Mocking everything including the system under test
• Testing only the happy path while ignoring error conditions