wehub-skill-sync
461 lines
16 KiB
Markdown
461 lines
16 KiB
Markdown
> **使用场景**：衡量 Playwright E2E 测试对应用程序代码的覆盖程度。适用于识别未经测试的代码路径，并在 CI 中强制执行覆盖率阈值。
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## 快速参考
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```bash
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# 安装覆盖率依赖
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npm install -D nyc istanbul-lib-coverage istanbul-reports v8-to-istanbul
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# 运行并收集覆盖率
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npx playwright test # 使用 fixture 收集覆盖率
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# 从收集的数据生成报告
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npx nyc report --reporter=html --reporter=text-summary
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npx nyc report --reporter=lcov # 用于 CI 集成（Codecov、SonarQube）
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# 检查覆盖率阈值
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npx nyc check-coverage --lines 80 --branches 70 --functions 75
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```
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## 模式
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### 模式 1：V8 覆盖率 + Playwright（推荐）
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**适用场景**：在 E2E 测试期间测量 Web 应用程序的代码覆盖率。V8 覆盖率利用 Chrome DevTools 协议实现准确的 JavaScript 覆盖率。
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**避免场景**：测试不受你控制的第三方站点。
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**第 1 步：创建覆盖率 fixture：**
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```ts
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// fixtures/coverage.ts
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import { test as base, expect } from "@playwright/test"
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import * as fs from "fs"
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import * as path from "path"
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import * as crypto from "crypto"
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const coverageDir = path.resolve(process.cwd(), ".nyc_output")
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export const test = base.extend({
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page: async ({ page, browserName }, use, testInfo) => {
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// V8 覆盖率仅在 Chromium 中有效
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if (browserName === "chromium") {
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await page.coverage.startJSCoverage({ resetOnNavigation: false })
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}
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await use(page)
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if (browserName === "chromium") {
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const coverage = await page.coverage.stopJSCoverage()
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// 过滤出仅属于应用程序的代码
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const appCoverage = coverage.filter(
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(entry) => entry.url.includes("localhost") && !entry.url.includes("node_modules")
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)
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if (appCoverage.length > 0) {
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// 确保输出目录存在
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fs.mkdirSync(coverageDir, { recursive: true })
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// 写入 V8 覆盖率数据
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const coverageFile = path.join(coverageDir, `coverage-${crypto.randomUUID()}.json`)
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fs.writeFileSync(
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coverageFile,
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JSON.stringify({
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result: appCoverage.map((entry) => ({
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scriptId: "0",
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url: entry.url,
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functions: entry.functions || [],
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})),
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})
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)
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}
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}
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},
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})
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export { expect }
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```
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**第 2 步：在测试中使用覆盖率 fixture：**
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```ts
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// tests/dashboard.spec.ts
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import { test, expect } from "../fixtures/coverage"
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test("仪表盘加载小部件", async ({ page }) => {
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await page.goto("/dashboard")
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await expect(page.getByRole("heading", { name: "Dashboard" })).toBeVisible()
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// 覆盖率会自动收集并保存
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})
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```
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**第 3 步：测试后生成覆盖率报告：**
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```json
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// package.json
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{
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"scripts": {
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"test:e2e": "npx playwright test",
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"test:coverage": "npx playwright test --project=chromium && npx nyc report --reporter=html --reporter=text-summary",
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"coverage:check": "npx nyc check-coverage --lines 80 --branches 70 --functions 75"
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}
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}
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```
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### 模式 2：Istanbul（基于 Source Map）覆盖率
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**适用场景**：你的应用程序使用 webpack、Vite 或其他打包工具，并且你需要与原始源文件关联的 source map 覆盖率。
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**避免场景**：V8 覆盖率已经足够——它的设置更简单。
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**第 1 步：对应用程序代码进行插桩：**
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对于 **Vite**：
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```bash
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npm install -D vite-plugin-istanbul
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```
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```ts
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// vite.config.ts
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import { defineConfig } from "vite"
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import istanbul from "vite-plugin-istanbul"
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export default defineConfig({
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plugins: [
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...(process.env.COVERAGE === "true"
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? [
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istanbul({
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include: "src/*",
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exclude: ["node_modules", "test/"],
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extension: [".js", ".ts", ".tsx", ".jsx"],
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requireEnv: true,
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}),
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]
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: []),
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],
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})
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```
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对于 **webpack**（Create React App）：
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```bash
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npm install -D @istanbuljs/nyc-config-typescript babel-plugin-istanbul
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```
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```json
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// babel.config.json（或 .babelrc）
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{
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"env": {
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"test": {
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"plugins": ["istanbul"]
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}
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}
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}
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```
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**第 2 步：从 `window.__coverage__` 收集覆盖率：**
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```ts
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// fixtures/istanbul-coverage.ts
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import { test as base, expect } from "@playwright/test"
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import * as fs from "fs"
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import * as path from "path"
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import * as crypto from "crypto"
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const coverageDir = path.resolve(process.cwd(), ".nyc_output")
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export const test = base.extend({
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page: async ({ page }, use) => {
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await use(page)
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// Istanbul 对代码进行插桩，并将覆盖率暴露在 window.__coverage__ 上
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const coverage = await page.evaluate(() => (window as any).__coverage__)
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if (coverage) {
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fs.mkdirSync(coverageDir, { recursive: true })
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const coverageFile = path.join(coverageDir, `coverage-${crypto.randomUUID()}.json`)
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fs.writeFileSync(coverageFile, JSON.stringify(coverage))
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}
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},
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})
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export { expect }
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```
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**第 3 步：配置 nyc：**
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```json
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// .nycrc.json
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{
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"extends": "@istanbuljs/nyc-config-typescript",
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"all": true,
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"include": ["src/**/*.{ts,tsx,js,jsx}"],
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"exclude": ["src/**/*.test.*", "src/**/*.spec.*", "src/test/**", "src/**/*.d.ts"],
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"reporter": ["html", "text-summary", "lcov"],
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"report-dir": "coverage"
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}
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```
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```bash
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# 使用插桩启动应用
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COVERAGE=true npm run dev
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# 运行测试（在另一个终端中，或等待开发服务器启动后）
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npx playwright test --project=chromium
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# 生成报告
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npx nyc report
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```
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### 模式 3：CI 中的覆盖率阈值
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**适用场景**：将最低覆盖率作为质量门禁强制执行。
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**避免场景**：你才刚刚开始接触覆盖率——请在建立基线之后再设置阈值。
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```json
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// .nycrc.json
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{
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"check-coverage": true,
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"lines": 80,
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"branches": 70,
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"functions": 75,
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"statements": 80,
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"reporter": ["html", "text-summary", "lcov"]
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}
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```
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**带覆盖率检查的 GitHub Actions：**
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```yaml
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# .github/workflows/playwright.yml（添加到测试任务步骤中）
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- name: 运行带覆盖率的 Playwright 测试
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run: COVERAGE=true npx playwright test --project=chromium
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- name: 生成覆盖率报告
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run: npx nyc report --reporter=html --reporter=text-summary --reporter=lcov
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if: ${{ !cancelled() }}
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- name: 检查覆盖率阈值
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run: npx nyc check-coverage --lines 80 --branches 70 --functions 75
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- name: 上传覆盖率报告
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uses: actions/upload-artifact@v4
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if: ${{ !cancelled() }}
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with:
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name: coverage-report
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path: coverage/
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retention-days: 14
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```
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### 模式 4：合并来自分片运行的覆盖率
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**适用场景**：测试在多台 CI 机器上分片运行，你需要聚合后的覆盖率。
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**避免场景**：测试在单台机器上运行。
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```yaml
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# .github/workflows/playwright.yml
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jobs:
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test:
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strategy:
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fail-fast: false
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matrix:
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shard: [1/4, 2/4, 3/4, 4/4]
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steps:
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# ... 检出、安装等
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- name: 运行带覆盖率的分片测试
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run: COVERAGE=true npx playwright test --shard=${{ matrix.shard }} --project=chromium
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- name: 上传覆盖率数据
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uses: actions/upload-artifact@v4
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if: ${{ !cancelled() }}
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with:
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name: coverage-${{ strategy.job-index }}
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path: .nyc_output/
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retention-days: 1
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merge-coverage:
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needs: test
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if: ${{ !cancelled() }}
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runs-on: ubuntu-latest
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steps:
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- uses: actions/checkout@v4
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- uses: actions/setup-node@v4
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with:
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node-version: 20
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cache: "npm"
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- run: npm ci
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- name: 下载所有覆盖率数据
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uses: actions/download-artifact@v4
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with:
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path: all-coverage
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pattern: coverage-*
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merge-multiple: true
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- name: 合并覆盖率
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run: |
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mkdir -p .nyc_output
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cp all-coverage/*.json .nyc_output/
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npx nyc report --reporter=html --reporter=text-summary --reporter=lcov
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npx nyc check-coverage --lines 80 --branches 70 --functions 75
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- name: 上传合并后的覆盖率报告
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uses: actions/upload-artifact@v4
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with:
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name: coverage-report
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path: coverage/
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retention-days: 14
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```
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### 模式 5：CSS 覆盖率
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**适用场景**：识别未使用的 CSS 以减小打包体积。
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**避免场景**：CSS 对你的应用程序来说不是性能问题。
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```ts
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// fixtures/css-coverage.ts
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import { test as base, expect } from "@playwright/test"
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import * as fs from "fs"
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import * as path from "path"
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export const test = base.extend({
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page: async ({ page, browserName }, use, testInfo) => {
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if (browserName === "chromium") {
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await page.coverage.startCSSCoverage()
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}
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await use(page)
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if (browserName === "chromium") {
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const coverage = await page.coverage.stopCSSCoverage()
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// 计算每个文件中未使用的 CSS 百分比
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const report = coverage.map((entry) => {
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const totalBytes = entry.text.length
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const usedBytes = entry.ranges.reduce((acc, range) => acc + (range.end - range.start), 0)
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return {
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url: entry.url,
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totalBytes,
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usedBytes,
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unusedPercent: ((1 - usedBytes / totalBytes) * 100).toFixed(1),
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}
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})
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// 保存以供分析
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const outputDir = path.resolve(process.cwd(), "css-coverage")
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fs.mkdirSync(outputDir, { recursive: true })
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fs.writeFileSync(
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path.join(outputDir, `${testInfo.testId}.json`),
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JSON.stringify(report, null, 2)
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)
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}
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},
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})
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export { expect }
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```
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## 决策指南
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| 覆盖率类型 | 工具 | 衡量内容 | 设置难度 | 准确性 |
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| -------------------------- | ------------------------------------------------ | --------------------- | -------- | -------------------- |
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| V8（Chrome DevTools） | `page.coverage` API | 浏览器中的 JS 执行 | 低 | 高（运行时） |
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| Istanbul（插桩） | `babel-plugin-istanbul` / `vite-plugin-istanbul` | 带 source map 的 JS | 中 | 高（源码级别） |
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| CSS | `page.coverage.startCSSCoverage()` | CSS 规则使用情况 | 低 | 高 |
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| 指标 | 衡量内容 | 推荐阈值 | 原因 |
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| ---------- | ---------------------- | -------- | -------------------------------------------------- |
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| Lines | 已执行的代码行数 | 80%+ | 最直观；可发现死代码 |
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| Branches | 已覆盖的 if/else 路径 | 70%+ | 可发现未测试的条件分支 |
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| Functions | 已调用的函数 | 75%+ | 可发现未使用的函数 |
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| Statements | 已执行的单个语句 | 80%+ | 与 lines 类似，但统计多语句行的每条语句 |
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| 场景 | 方案 | 原因 |
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| ------------------------------ | -------------------------------- | -------------------------------------- |
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| 刚刚开始接触覆盖率 | V8 覆盖率，不设阈值 | 先建立基线 |
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| 成熟的代码库 | Istanbul + CI 中的阈值 | 基于 source map，强制执行 |
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| 分片 CI | 合并所有分片后的 `.nyc_output` | 聚合后的覆盖率视图 |
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| 只关心 Chromium | V8 覆盖率 fixture | 设置最简单，无需修改构建 |
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| 需要源码级别的准确性 | Istanbul + 打包工具插件 | 映射回原始源文件 |
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| 上传到 Codecov / SonarQube | 生成 `lcov` 格式 | 覆盖率服务的标准格式 |
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## 反模式
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| 反模式 | 问题 | 推荐做法 |
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| ------------------------------------------- | ----------------------------------------------------- | ------------------------------------------------------------------------------------ |
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| 追求 100% E2E 覆盖率 | E2E 测试成本高，超过 80% 后收益递减 | 设定合理的阈值；用单元测试覆盖边界情况 |
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| 在所有浏览器中收集覆盖率 | V8 覆盖率仅在 Chromium 中有效，其他浏览器浪费资源 | 仅在 `--project=chromium` 下运行覆盖率收集 |
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| 未过滤源文件 | 覆盖率包含 `node_modules` 和第三方代码 | 过滤：`entry.url.includes('localhost') && !entry.url.includes('node_modules')` |
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| 覆盖率拖慢 CI 却未产生价值 | 在每个 PR 上都收集覆盖率但没有设置阈值 | 要么强制执行阈值，要么跳过覆盖率收集 |
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| 在生产构建中启用 Istanbul 插桩 | 性能开销；暴露内部实现 | 仅在 `COVERAGE=true` 时进行插桩 |
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| 仅靠 E2E 覆盖率衡量 | E2E 测试覆盖的是 happy path，单元测试覆盖的是分支 | 将 E2E 覆盖率与单元测试覆盖率结合使用 |
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## 故障排除
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### 覆盖率报告显示 0% 或为空
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**原因（V8）**：测试未使用覆盖率 fixture，或者未调用 `startJSCoverage()`。
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**修复**：确保测试从覆盖率 fixture 文件导入，而不是直接从 `@playwright/test` 导入：
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```ts
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// 使用这个：
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import { test, expect } from "../fixtures/coverage"
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// 不要用这个：
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import { test, expect } from "@playwright/test"
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```
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**原因（Istanbul）**：应用程序未进行插桩，或者 `window.__coverage__` 为 undefined。
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**修复**：确认应用程序已启用插桩运行：
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```bash
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# 检查覆盖率是否已暴露
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COVERAGE=true npm run dev
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# 在浏览器控制台中：window.__coverage__ -> 应该是一个对象，而不是 undefined
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```
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### 覆盖率文件无法正确合并
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**原因**：来自不同分片的覆盖率 JSON 文件格式不兼容或键重叠。
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**修复**：确保所有分片使用唯一的文件名写入 `.nyc_output/`：
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```ts
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const coverageFile = path.join(coverageDir, `coverage-${crypto.randomUUID()}.json`)
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```
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然后使用 `npx nyc report` 合并（它会读取 `.nyc_output/` 中的所有文件）。
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### V8 覆盖率无法映射回源文件
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**原因**：V8 覆盖率报告的是打包/编译后的 URL，而不是原始源文件。
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**修复**：改用 Istanbul 插桩以获得源码级别的准确性，或者使用 `v8-to-istanbul` 进行转换：
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```bash
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npm install -D v8-to-istanbul
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```
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### 并行运行时代码覆盖率下降
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**原因**：如果文件名冲突，并行 worker 会互相覆盖覆盖率文件。
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**修复**：在文件名中包含 `workerInfo.workerIndex` 或 UUID：
|
||
|
||
```ts
|
||
const coverageFile = path.join(
|
||
coverageDir,
|
||
`coverage-worker${workerInfo.workerIndex}-${crypto.randomUUID()}.json`
|
||
)
|
||
```
|
||
|
||
## 相关文档
|
||
|
||
- [ci/parallel-and-sharding.md](parallel-and-sharding.md) —— 从分片运行中合并覆盖率
|
||
- [ci/ci-github-actions.md](ci-github-actions.md) —— CI 中的覆盖率阈值
|
||
- [ci/reporting-and-artifacts.md](reporting-and-artifacts.md) —— 上传覆盖率报告
|
||
- [core/configuration.md](../core/configuration.md) —— 覆盖率的项目配置
|
||
- [core/test-architecture.md](../core/test-architecture.md) —— E2E 与单元测试覆盖率策略
|