testing

name	testing
description	Write and run tests including unit tests, integration tests, and E2E tests. Use when ensuring code quality, writing test cases, or setting up testing frameworks.

🧪 Testing Skill

Test Types

Type	Purpose	Tools
Unit	Test functions in isolation	Jest, Vitest, pytest
Integration	Test modules together	Supertest, pytest
E2E	Test full user flows	Playwright, Cypress

---

Unit Test Patterns

JavaScript/TypeScript (Jest/Vitest)

describe('calculateTotal', () => {
  it('should add tax correctly', () => {
    expect(calculateTotal(100, 0.07)).toBe(107);
  });

  it('should handle zero price', () => {
    expect(calculateTotal(0, 0.07)).toBe(0);
  });

  it('should throw on negative price', () => {
    expect(() => calculateTotal(-10, 0.07)).toThrow();
  });
});

Python (pytest)

def test_calculate_total():
    assert calculate_total(100, 0.07) == 107

def test_calculate_total_zero():
    assert calculate_total(0, 0.07) == 0

def test_calculate_total_negative():
    with pytest.raises(ValueError):
        calculate_total(-10, 0.07)

---

Test Structure (AAA Pattern)

test('should upload file successfully', async () => {
  // Arrange
  const file = createMockFile('video.mp4');
  const uploader = new Uploader();

  // Act
  const result = await uploader.upload(file);

  // Assert
  expect(result.success).toBe(true);
  expect(result.url).toContain('uploaded');
});

---

Mocking

// Mock function
const mockFetch = jest.fn().mockResolvedValue({ ok: true });

// Mock module
jest.mock('./api', () => ({
  fetchData: jest.fn().mockResolvedValue({ data: [] })
}));

// Mock timer
jest.useFakeTimers();
jest.advanceTimersByTime(3000);

---

E2E Testing (Playwright)

test('upload flow', async ({ page }) => {
  await page.goto('https://tiktok.com/upload');
  
  // Upload file
  await page.setInputFiles('input[type="file"]', 'video.mp4');
  
  // Fill form
  await page.fill('[placeholder="Title"]', 'My Video');
  
  // Submit
  await page.click('button:has-text("Post")');
  
  // Verify
  await expect(page.locator('.success')).toBeVisible();
});

---

Test Checklist

• Happy path covered
• Edge cases (null, empty, boundary)
• Error cases
• Async behavior
• Mocks cleaned up

---

🤖 AI Test Generation

Auto-Generate Test Cases

// Given a function like:
function validateEmail(email) {
  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(email);
}

// AI generates these test cases:
describe('validateEmail', () => {
  // Happy path
  test('valid email returns true', () => {
    expect(validateEmail('[e-mail]')).toBe(true);
  });
  
  // Edge cases
  test.each([
    ['', false],                    // empty
    ['user', false],                // no @
    ['user@', false],               // no domain
    ['@example.com', false],        // no user
    ['user@example', false],        // no TLD
    ['[e-mail]', true], // multiple dots
  ])('validateEmail(%s) = %s', (input, expected) => {
    expect(validateEmail(input)).toBe(expected);
  });
});

---

📊 Coverage Analysis

Commands

# Jest coverage
npm test -- --coverage

# Vitest coverage
npx vitest --coverage

# NYC coverage
npx nyc npm test

Coverage Targets

Metric	Minimum	Good
Statements	70%	90%+
Branches	70%	85%+
Functions	70%	90%+
Lines	70%	90%+

---

📸 Snapshot Testing

// Generate snapshot
test('component renders correctly', () => {
  const tree = render(<Button label="Click me" />);
  expect(tree).toMatchSnapshot();
});

// Update snapshots
// npm test -- -u

---

Test Commands

# Run all tests
npm test

# Run specific file
npm test -- button.test.js

# Watch mode
npm test -- --watch

# Update snapshots
npm test -- -u

# Coverage report
npm test -- --coverage --coverageReporters=text