extension-test

Extension Testing

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Testing Layer Architecture

Unit Tests (Jest)          → Test isolated logic, chrome.* API mocks
Integration Tests (Jest)   → Test service interactions, message passing
E2E Tests (Puppeteer)      → Test in real Chrome with extension loaded

Critical constraint: Extensions CANNOT run in headless mode. E2E requires headless: false or Chrome's --headless=new (Chrome 112+).

---

Layer 1: Unit + Integration (Jest)

Install

npm install -D jest @types/jest ts-jest jest-chrome
# For React popup:
npm install -D @testing-library/react @testing-library/jest-dom jsdom

jest.config.ts

export default {
  preset: "ts-jest",
  testEnvironment: "jsdom",
  setupFilesAfterEnv: ["./jest.setup.ts"],
  moduleNameMapper: {
    "^@/(.*)$": "<rootDir>/src/$1",
  },
};

jest.setup.ts (minimal)

import chrome from "jest-chrome";
Object.assign(global, { chrome });

Full mock setup → chrome-api-mocks.md Unit/integration patterns → unit-integration-testing.md

---

Layer 2: E2E (Puppeteer)

Install

npm install -D puppeteer

Launch extension in Chrome

import puppeteer from "puppeteer";
import path from "path";

const browser = await puppeteer.launch({
  headless: false, // extensions require non-headless
  args: [
    `--disable-extensions-except=${path.resolve("dist")}`,
    `--load-extension=${path.resolve("dist")}`,
  ],
});

Get extension ID

const targets = await browser.targets();
const extTarget = targets.find((t) => t.type() === "service_worker");
const extUrl = extTarget?.url() ?? "";
const [, , extId] = extUrl.split("/");

Full E2E patterns → e2e-testing-puppeteer.md

---

Chrome API Mocking Strategy

API	Approach
chrome.storage	Mock with in-memory store
chrome.runtime.sendMessage	jest.fn() + mock response
chrome.tabs	jest.fn() with createMockTab helper
chrome.action	jest.fn() stubs
chrome.alarms	jest.fn() stubs

All mocks → chrome-api-mocks.md

---

package.json Scripts

{
  "scripts": {
    "test:unit": "jest --testPathPattern=unit",
    "test:integration": "jest --testPathPattern=integration",
    "test:e2e": "jest --testPathPattern=e2e --runInBand",
    "test": "npm run test:unit && npm run test:integration"
  }
}

Run E2E separately (--runInBand) — Puppeteer tests must run serially.

---

Reference Files

• unit-integration-testing.md — Jest patterns, mocking, component tests
• e2e-testing-puppeteer.md — Puppeteer setup, popup/content/SW tests
• chrome-api-mocks.md — Full chrome.* mock templates