Vitest

Vitest Best Practices Guide (4.x)

版本資訊

• 最新穩定版：Vitest 4.1.2（2026-03）
• Vitest 4.0 新增：Browser Mode 穩定化、toMatchScreenshot()、expect.schemaMatching、expect.assert

安裝

npm install -D vitest @vitest/coverage-v8

設定（vitest.config.ts）

import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    environment: 'node',
    globals: true,
    include: ['src/**/*.{test,spec}.{ts,tsx}'],
    exclude: ['node_modules', 'dist', 'e2e'],
    restoreMocks: true, // 自動還原 mock
    pool: 'forks',      // 預設，最安全

    coverage: {
      provider: 'v8',
      include: ['src/**/*.ts'],
      exclude: ['src/**/*.d.ts', 'src/**/*.test.ts'],
      thresholds: { statements: 80, branches: 80, functions: 80, lines: 80 },
    },
  },
});

Astro 整合

import { getViteConfig } from 'astro/config';

export default getViteConfig({
  test: { /* vitest options */ },
});

測試 Astro 元件（Container API，Astro 4.9+）

import { experimental_AstroContainer as AstroContainer } from 'astro/container';
import Card from '../src/components/Card.astro';

test('Card renders', async () => {
  const container = await AstroContainer.create();
  const html = await container.renderToString(Card, {
    slots: { default: 'content' },
  });
  expect(html).toContain('content');
});

Mocking

vi.fn() — 獨立 mock function

const handler = vi.fn();
handler('arg');
expect(handler).toHaveBeenCalledWith('arg');

vi.spyOn() — 觀察既有方法

const spy = vi.spyOn(console, 'log');
doSomething();
expect(spy).toHaveBeenCalledWith('expected');

vi.mock() — 替換整個模組（會被 hoisted）

vi.mock('./api', () => ({
  fetchData: vi.fn().mockResolvedValue({ id: 1 }),
}));

清理層級

建議：設定 restoreMocks: true 自動還原。

測試 Async / Timers / Fetch

Async

it('fetches data', async () => {
  const data = await fetchUser(1);
  expect(data.name).toBe('Alice');
});

Fake Timers

it('debounce', () => {
  vi.useFakeTimers();
  const fn = vi.fn();
  debounce(fn, 300)();
  vi.advanceTimersByTime(300);
  expect(fn).toHaveBeenCalledOnce();
  vi.useRealTimers();
});

Mock fetch

vi.stubGlobal('fetch', vi.fn().mockResolvedValue({
  ok: true,
  json: () => Promise.resolve({ data: 'test' }),
}));

測試 Three.js / WebGL 程式

WebGL 在 Node.js 不可用，策略：

Mock Renderer

vi.mock('three', async (importOriginal) => {
  const actual = await importOriginal<typeof import('three')>();
  return {
    ...actual,
    WebGLRenderer: vi.fn().mockImplementation(() => ({
      setSize: vi.fn(),
      render: vi.fn(),
      domElement: document.createElement('canvas'),
      dispose: vi.fn(),
      setPixelRatio: vi.fn(),
    })),
  };
});

原則：將場景邏輯（物件位置、層級、材質）與渲染分開測試。Mock WebGLRenderer，專注測試 scene graph。

測試 Node.js 腳本（如 data collection）

vi.mock('node:fs/promises', () => ({
  readFile: vi.fn().mockResolvedValue('content'),
  writeFile: vi.fn().mockResolvedValue(undefined),
}));

vi.stubGlobal('fetch', vi.fn().mockResolvedValue({
  ok: true,
  json: () => Promise.resolve([{ id: 1 }]),
}));

import { collectData } from './collect';

it('collects data', async () => {
  const result = await collectData();
  expect(result).toHaveLength(1);
});

Workspace / Projects

export default defineConfig({
  test: {
    projects: [
      {
        extends: true,
        test: { name: 'unit', include: ['src/**/*.unit.test.ts'], environment: 'node' },
      },
      {
        extends: true,
        test: { name: 'components', include: ['src/**/*.component.test.ts'], environment: 'jsdom' },
      },
    ],
  },
});

執行特定 project：vitest --project unit

Coverage：v8 vs Istanbul

建議用 v8。忽略特定行：/* v8 ignore next */

DOM 測試環境

• happy-dom：較快，大多數情況適用
• jsdom：DOM 實作更完整

// 單檔覆蓋
// @vitest-environment happy-dom

Snapshot Testing

expect(result).toMatchSnapshot();           // 檔案 snapshot
expect(result).toMatchInlineSnapshot();     // inline（自動填入）
expect(html).toMatchFileSnapshot('./expected.html'); // 自訂檔案

更新：vitest -u

In-Source Testing

export function add(a: number, b: number) { return a + b; }

if (import.meta.vitest) {
  const { it, expect } = import.meta.vitest;
  it('adds', () => expect(add(1, 2)).toBe(3));
}

設定：includeSource: ['src/**/*.ts'] Production 移除：define: { 'import.meta.vitest': 'undefined' }

效能優化

常見陷阱

1. vi.mock() 被 hoisted — 不能用下方宣告的變數
2. fetch + threads pool — 會 "Failed to terminate worker"，改用 forks
3. Native modules + threads — segfault，改用 forks
4. path alias 找不到 — 安裝 vite-tsconfig-paths
5. 忘記 await async — 用 expect().rejects 處理預期錯誤

Type Testing

檔名：*.test-d.ts，執行：vitest --typecheck

import { expectTypeOf } from 'vitest';
expectTypeOf(add).parameter(0).toBeNumber();
expectTypeOf(add(1, 2)).toEqualTypeOf<number>();