extension-test

---
name: extension-test
description: Set up and run unit, integration, and E2E tests for Chrome extensions. Covers Jest mocks for chrome.* APIs and Puppeteer E2E with real Chrome.
license: MIT
---

# 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+).

---

## Layer 1: Unit + Integration (Jest)

### Install

```bash
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

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

### jest.setup.ts (minimal)

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

Full mock setup → [chrome-api-mocks.md](references/chrome-api-mocks.md)
Unit/integration patterns → [unit-integration-testing.md](references/unit-integration-testing.md)

---

## Layer 2: E2E (Puppeteer)

### Install

```bash
npm install -D puppeteer
```

### Launch extension in Chrome

```ts
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

```ts
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](references/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](references/chrome-api-mocks.md)

---

## package.json Scripts

```json
{
  "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](references/unit-integration-testing.md) — Jest patterns, mocking, component tests
- [e2e-testing-puppeteer.md](references/e2e-testing-puppeteer.md) — Puppeteer setup, popup/content/SW tests
- [chrome-api-mocks.md](references/chrome-api-mocks.md) — Full chrome.* mock templates