testing-strategies

Testing pyramid, patterns, and practices for building reliable software.

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Install skill "testing-strategies" with this command: npx skills add miles990/claude-software-skills/miles990-claude-software-skills-testing-strategies

Testing Strategies

Overview

Testing pyramid, patterns, and practices for building reliable software.

Testing Pyramid

       /\
      /  \
     / E2E\        Few, slow, expensive
    /──────\
   /        \
  /Integration\    Some, medium speed
 /──────────────\
/                \

/ Unit Tests \ Many, fast, cheap /____________________\

Level Speed Scope Quantity

Unit Fast (ms) Single function/class Many (70%)

Integration Medium (s) Multiple components Some (20%)

E2E Slow (min) Full system Few (10%)

Unit Testing

Structure: Arrange-Act-Assert

describe('calculateDiscount', () => { it('applies 10% discount for orders over $100', () => { // Arrange const order = { items: [{ price: 150 }] }; const discountService = new DiscountService();

// Act
const result = discountService.calculateDiscount(order);

// Assert
expect(result).toBe(15);

});

it('returns 0 for orders under $100', () => { // Arrange const order = { items: [{ price: 50 }] }; const discountService = new DiscountService();

// Act
const result = discountService.calculateDiscount(order);

// Assert
expect(result).toBe(0);

}); });

Mocking

// Mock dependencies const mockEmailService = { send: jest.fn().mockResolvedValue({ success: true }) };

const mockUserRepo = { findById: jest.fn().mockResolvedValue({ id: '1', email: 'test@example.com' }) };

describe('NotificationService', () => { let service: NotificationService;

beforeEach(() => { jest.clearAllMocks(); service = new NotificationService(mockEmailService, mockUserRepo); });

it('sends email to user', async () => { await service.notifyUser('1', 'Hello!');

expect(mockUserRepo.findById).toHaveBeenCalledWith('1');
expect(mockEmailService.send).toHaveBeenCalledWith(
  'test@example.com',
  'Hello!'
);

});

it('throws when user not found', async () => { mockUserRepo.findById.mockResolvedValue(null);

await expect(service.notifyUser('999', 'Hello!'))
  .rejects.toThrow('User not found');

}); });

Testing Edge Cases

describe('parseAge', () => { // Happy path it('parses valid age string', () => { expect(parseAge('25')).toBe(25); });

// Edge cases it('handles zero', () => { expect(parseAge('0')).toBe(0); });

it('handles boundary values', () => { expect(parseAge('1')).toBe(1); expect(parseAge('150')).toBe(150); });

// Error cases it('throws on negative numbers', () => { expect(() => parseAge('-5')).toThrow('Age cannot be negative'); });

it('throws on non-numeric input', () => { expect(() => parseAge('abc')).toThrow('Invalid age format'); });

it('throws on empty string', () => { expect(() => parseAge('')).toThrow('Age is required'); });

// Null/undefined it('throws on null', () => { expect(() => parseAge(null as any)).toThrow(); }); });

Integration Testing

API Testing

import request from 'supertest'; import { app } from '../app'; import { db } from '../database';

describe('POST /api/users', () => { beforeEach(async () => { await db.users.deleteMany({}); });

afterAll(async () => { await db.disconnect(); });

it('creates a new user', async () => { const response = await request(app) .post('/api/users') .send({ email: 'test@example.com', name: 'Test User' }) .expect(201);

expect(response.body).toMatchObject({
  id: expect.any(String),
  email: 'test@example.com',
  name: 'Test User'
});

// Verify in database
const user = await db.users.findOne({ email: 'test@example.com' });
expect(user).not.toBeNull();

});

it('returns 400 for invalid email', async () => { const response = await request(app) .post('/api/users') .send({ email: 'invalid-email', name: 'Test User' }) .expect(400);

expect(response.body.error).toBe('Invalid email format');

});

it('returns 409 for duplicate email', async () => { // Create first user await request(app) .post('/api/users') .send({ email: 'test@example.com', name: 'First' });

// Try to create duplicate
const response = await request(app)
  .post('/api/users')
  .send({ email: 'test@example.com', name: 'Second' })
  .expect(409);

expect(response.body.error).toBe('Email already exists');

}); });

Database Testing with Testcontainers

import { PostgreSqlContainer } from '@testcontainers/postgresql'; import { Pool } from 'pg';

describe('UserRepository', () => { let container: StartedPostgreSqlContainer; let pool: Pool; let repo: UserRepository;

beforeAll(async () => { container = await new PostgreSqlContainer().start(); pool = new Pool({ connectionString: container.getConnectionUri() }); await runMigrations(pool); repo = new UserRepository(pool); }, 60000);

afterAll(async () => { await pool.end(); await container.stop(); });

beforeEach(async () => { await pool.query('TRUNCATE users CASCADE'); });

it('creates and retrieves user', async () => { const created = await repo.create({ email: 'test@example.com', name: 'Test' });

const found = await repo.findById(created.id);

expect(found).toEqual(created);

}); });

E2E Testing

Playwright

import { test, expect } from '@playwright/test';

test.describe('User Authentication', () => { test('successful login flow', async ({ page }) => { await page.goto('/login');

// Fill form
await page.fill('[data-testid="email-input"]', 'user@example.com');
await page.fill('[data-testid="password-input"]', 'password123');

// Submit
await page.click('[data-testid="login-button"]');

// Verify redirect to dashboard
await expect(page).toHaveURL('/dashboard');
await expect(page.locator('[data-testid="welcome-message"]'))
  .toContainText('Welcome, user@example.com');

});

test('shows error for invalid credentials', async ({ page }) => { await page.goto('/login');

await page.fill('[data-testid="email-input"]', 'wrong@example.com');
await page.fill('[data-testid="password-input"]', 'wrongpassword');
await page.click('[data-testid="login-button"]');

await expect(page.locator('[data-testid="error-message"]'))
  .toBeVisible()
  .toContainText('Invalid credentials');

}); });

test.describe('Shopping Cart', () => { test('add item and checkout', async ({ page }) => { // Setup - login await page.goto('/login'); await page.fill('[data-testid="email-input"]', 'buyer@example.com'); await page.fill('[data-testid="password-input"]', 'password'); await page.click('[data-testid="login-button"]');

// Browse products
await page.goto('/products');
await page.click('[data-testid="product-1"] [data-testid="add-to-cart"]');

// Verify cart
await expect(page.locator('[data-testid="cart-count"]')).toHaveText('1');

// Checkout
await page.click('[data-testid="cart-icon"]');
await page.click('[data-testid="checkout-button"]');

// Fill shipping
await page.fill('[data-testid="address"]', '123 Test St');
await page.click('[data-testid="place-order"]');

// Verify success
await expect(page).toHaveURL(/\/orders\/\d+/);
await expect(page.locator('[data-testid="order-status"]'))
  .toContainText('Order Confirmed');

}); });

Visual Regression Testing

import { test, expect } from '@playwright/test';

test('homepage visual regression', async ({ page }) => { await page.goto('/');

// Wait for dynamic content await page.waitForSelector('[data-testid="hero-section"]');

// Take screenshot and compare await expect(page).toHaveScreenshot('homepage.png', { maxDiffPixels: 100, threshold: 0.2 }); });

test('responsive design', async ({ page }) => { await page.setViewportSize({ width: 375, height: 667 }); // iPhone SE await page.goto('/');

await expect(page).toHaveScreenshot('homepage-mobile.png'); });

Test-Driven Development (TDD)

Red-Green-Refactor Cycle

// 1. RED - Write failing test first test('passwordValidator rejects passwords without numbers', () => { const result = validatePassword('NoNumbers!'); expect(result.valid).toBe(false); expect(result.errors).toContain('Must contain at least one number'); });

// 2. GREEN - Write minimal code to pass function validatePassword(password: string): ValidationResult { const errors: string[] = [];

if (!/\d/.test(password)) { errors.push('Must contain at least one number'); }

return { valid: errors.length === 0, errors }; }

// 3. REFACTOR - Improve code quality const VALIDATION_RULES = [ { pattern: /\d/, message: 'Must contain at least one number' }, { pattern: /[A-Z]/, message: 'Must contain at least one uppercase letter' }, { pattern: /[a-z]/, message: 'Must contain at least one lowercase letter' }, { pattern: /.{8,}/, message: 'Must be at least 8 characters' } ];

function validatePassword(password: string): ValidationResult { const errors = VALIDATION_RULES .filter(rule => !rule.pattern.test(password)) .map(rule => rule.message);

return { valid: errors.length === 0, errors }; }

Testing Patterns

Test Fixtures

// fixtures/users.ts export const validUser = { email: 'test@example.com', name: 'Test User', role: 'user' };

export const adminUser = { ...validUser, role: 'admin', email: 'admin@example.com' };

// In tests import { validUser, adminUser } from '../fixtures/users';

describe('UserService', () => { it('creates user with valid data', async () => { const result = await service.create(validUser); expect(result.email).toBe(validUser.email); }); });

Factory Functions

// factories/user.factory.ts import { faker } from '@faker-js/faker';

export function createUser(overrides: Partial<User> = {}): User { return { id: faker.string.uuid(), email: faker.internet.email(), name: faker.person.fullName(), createdAt: faker.date.past(), ...overrides }; }

// In tests it('handles users with long names', () => { const user = createUser({ name: 'A'.repeat(100) }); const result = formatUserCard(user); expect(result.displayName).toHaveLength(50); // Truncated });

Testing Async Code

// Async/await it('fetches user data', async () => { const user = await userService.getById('123'); expect(user.name).toBe('John'); });

// Promises it('fetches user data', () => { return userService.getById('123').then(user => { expect(user.name).toBe('John'); }); });

// Testing rejected promises it('throws on invalid id', async () => { await expect(userService.getById('invalid')) .rejects.toThrow('User not found'); });

// Waiting for side effects it('debounces search input', async () => { const onSearch = jest.fn(); render(<SearchBox onSearch={onSearch} debounceMs={300} />);

await userEvent.type(screen.getByRole('textbox'), 'test');

// Should not have called yet expect(onSearch).not.toHaveBeenCalled();

// Wait for debounce await waitFor(() => { expect(onSearch).toHaveBeenCalledWith('test'); }, { timeout: 500 }); });

Code Coverage

Coverage Metrics

Metric What It Measures

Line Percentage of lines executed

Branch Percentage of if/else branches taken

Function Percentage of functions called

Statement Percentage of statements executed

Jest Configuration

// jest.config.js module.exports = { collectCoverageFrom: [ 'src//*.{ts,tsx}', '!src//.d.ts', '!src/**/.stories.tsx', '!src/test/**' ], coverageThreshold: { global: { branches: 80, functions: 80, lines: 80, statements: 80 } } };

Related Skills

  • [[code-quality]] - Writing testable code

  • [[devops-cicd]] - CI integration

  • [[performance-optimization]] - Performance testing

Sharp Edges（常見陷阱）

這些是測試中最常見且代價最高的錯誤

SE-1: 測試實作而非行為

  • 嚴重度: high

  • 情境: 測試過度耦合內部實作，重構時測試全部壞掉

  • 原因: 測試私有方法、mock 太細、驗證內部狀態

  • 症狀:

  • 改了一行程式碼，10 個測試失敗

  • 測試檔案比程式碼還長

  • 重構時花更多時間修測試

  • 檢測: expect.*.toHaveBeenCalledTimes(\d{2,})|mock.*private|spy.*internal

  • 解法: 測試公開 API/行為、使用 black-box testing、減少 mock 數量

SE-2: 假陽性測試 (False Positive)

  • 嚴重度: critical

  • 情境: 測試永遠通過，但實際上沒有驗證任何東西

  • 原因: 忘記 await、expect 沒有執行、條件判斷錯誤

  • 症狀:

  • 測試通過但 bug 仍然存在

  • 刪掉測試中的關鍵 assertion 測試還是通過

  • Coverage 高但信心低

  • 檢測: it(.{\s})|expect(.*)(?!.)|.resolves(?!.)|.rejects(?!.)

  • 解法: TDD（先寫失敗的測試）、review 測試程式碼、使用 ESLint no-floating-promises

SE-3: Flaky Tests（不穩定測試）

  • 嚴重度: high

  • 情境: 測試有時通過有時失敗，沒有程式碼變更

  • 原因: 依賴時間、依賴外部服務、競態條件、共享狀態

  • 症狀:

  • CI 需要 retry 才能通過

  • 本地通過但 CI 失敗

  • 團隊開始忽略失敗的測試

  • 檢測: new Date()|Date.now()|setTimeout.*\d{4,}|sleep(\d+)

  • 解法: 使用 fake timers、隔離測試狀態、避免 hard-coded delays、mock 外部依賴

SE-4: 測試金字塔倒置

  • 嚴重度: medium

  • 情境: E2E 測試太多，單元測試太少，CI 超慢

  • 原因: 「E2E 測試更接近真實」的誤解、不想寫單元測試

  • 症狀:

  • CI 跑 30+ 分鐘

  • 測試失敗難以定位問題

  • E2E 測試經常 flaky

  • 檢測: describe.*E2E|playwright.*test|cypress.*it (數量遠超 unit test)

  • 解法: 遵循 70% unit / 20% integration / 10% E2E 比例、E2E 只測關鍵路徑

SE-5: 過度 Mocking

  • 嚴重度: medium

  • 情境: Mock 太多導致測試失去意義，只是在測試 mock

  • 原因: 為了隔離而 mock 所有依賴、測試執行時間焦慮

  • 症狀:

  • 測試通過但整合時失敗

  • Mock 的行為與真實行為不符

  • 更新依賴後 mock 過時

  • 檢測: jest.mock.*jest.mock.jest.mock|mock(.).mock(.).*mock(

  • 解法: 只 mock 外部依賴（網路、檔案系統）、使用真實的 in-memory 實作、寫更多整合測試

Validations

V-1: 禁止空的測試

  • 類型: regex

  • 嚴重度: critical

  • 模式: (it|test)\s*([^)]+,\s*(async\s*)?()\s*=>\s*{\s*}\s*)

  • 訊息: Empty test detected - test has no assertions

  • 修復建議: Add meaningful assertions with expect()

  • 適用: *.test.ts , *.test.js , *.spec.ts , *.spec.js

V-2: 測試缺少 assertion

  • 類型: regex

  • 嚴重度: high

  • 模式: (it|test)\s*([^)]+,\s*(async\s*)?()\s*=>\s*{[^}]*}(?![^}]*expect)

  • 訊息: Test without expect() assertion may be a false positive

  • 修復建議: Add at least one expect() assertion

  • 適用: *.test.ts , *.test.js , *.spec.ts , *.spec.js

V-3: 禁止 fit/fdescribe (focused tests)

  • 類型: regex

  • 嚴重度: critical

  • 模式: \b(fit|fdescribe|it.only|describe.only|test.only)\s*(

  • 訊息: Focused test will skip other tests in CI

  • 修復建議: Remove f prefix or .only before committing

  • 適用: *.test.ts , *.test.js , *.spec.ts , *.spec.js

V-4: 禁止 skip tests 無說明

  • 類型: regex

  • 嚴重度: medium

  • 模式: (xit|xdescribe|it.skip|describe.skip|test.skip)\s*([^)]+)

  • 訊息: Skipped test without documented reason

  • 修復建議: Add comment explaining why test is skipped and tracking issue

  • 適用: *.test.ts , *.test.js , *.spec.ts , *.spec.js

V-5: 測試中使用 setTimeout

  • 類型: regex

  • 嚴重度: high

  • 模式: setTimeout\s*(\s*[^,]+,\s*\d{3,}\s*)

  • 訊息: Hard-coded delays in tests cause flakiness and slow tests

  • 修復建議: Use jest.useFakeTimers() or waitFor() from testing-library

  • 適用: *.test.ts , *.test.js , *.spec.ts , *.spec.js

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