Extension Testing

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+).

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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

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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

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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

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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.

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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