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

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

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

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

npm install -D puppeteer

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')}`,
  ],
});

const targets = await browser.targets();
const extTarget = targets.find(t => t.type() === 'service_worker');
const extUrl = extTarget?.url() ?? '';
const [, , extId] = extUrl.split('/');

{
  "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"
  }
}