Writing Automated Tests

JavaScript
// Example: Testing a user registration function
const { createUser, validateEmail } = require('./user-service');

describe('User Registration', () => {
  test('creates user with valid data', async () => {
    const userData = { email: 'test@example.com', password: 'SecurePass123!' };
    const user = await createUser(userData);
    
    expect(user.id).toBeDefined();
    expect(user.email).toBe('test@example.com');
    expect(user.password).not.toBe(userData.password); // Should be hashed
  });

  test('rejects invalid email formats', () => {
    expect(validateEmail('invalid-email')).toBe(false);
    expect(validateEmail('test@example.com')).toBe(true);
  });
});

Progress:

• Set up testing framework (Jest, pytest, etc.)
• Configure static analysis tools (TypeScript, ESLint, mypy)
• Write unit tests for core business logic
• Add integration tests for critical user flows
• Set up automated test runs in CI/CD
• Monitor test coverage and maintenance burden

Test Writing Process:

1. Start with static typing - Use TypeScript, Python type hints, or similar
2. Add linting - ESLint, pylint, or language-specific tools
3. Test business logic first - Focus on functions that contain your core rules
4. Test error conditions - Invalid inputs, network failures, edge cases
5. Integration tests last - Full user flows, database interactions

Example 1: Unit Test Input: Payment processing function Output:

Python
def test_process_payment():
    # Happy path
    result = process_payment(100.00, "valid_card_token")
    assert result.success == True
    assert result.transaction_id is not None
    
    # Error cases
    with pytest.raises(InvalidAmountError):
        process_payment(-10.00, "valid_card_token")

Example 2: Integration Test Input: User checkout flow Output:

JavaScript
test('complete checkout process', async () => {
  const user = await createTestUser();
  const product = await createTestProduct();
  
  await addToCart(user.id, product.id);
  const order = await checkout(user.id, testPaymentMethod);
  
  expect(order.status).toBe('completed');
  expect(order.total).toBe(product.price);
});

• Confidence over coverage - 100% coverage doesn't mean bug-free code
• Test behavior, not implementation - Focus on what the code should do, not how
• Keep tests simple - Each test should verify one specific behavior
• Use descriptive test names - should_reject_expired_credit_cards not test_payment
• Fast feedback loop - Unit tests should run in seconds, not minutes
• Mock external dependencies - Don't hit real APIs or databases in unit tests

• Testing framework code - Don't test library functions, test YOUR logic
• Brittle tests - Tests that break when you refactor working code
• Testing too much implementation detail - Mock every single function call
• Ignoring edge cases - Empty arrays, null values, boundary conditions
• No static analysis - Writing tests without TypeScript/linting is doing it the hard way
• All or nothing mentality - Start small, add tests incrementally to existing projects