service-worker-mock

Service Worker Mock

A mock service worker environment generator.

Why?

Testing service workers is difficult. Each file produces side-effects by calls to self.addEventListener, and the service worker environment is unlike a normal web or node context. This package makes it easy to turn a Node.js environment into a faux service worker environment. Additionally, it adds some helpful methods for testing integrations.

The service worker mock creates an environment with the following properties, based on the current Mozilla Service Worker Docs.

const env = {
  // Environment polyfills
  skipWaiting: Function,
  caches: CacheStorage,
  clients: Clients,
  registration: ServiceWorkerRegistration,
  addEventListener: Function,
  Request: constructor Function,
  Response: constructor Function,
  URL: constructor Function,

  // Test helpers
  listeners: Object,
  trigger: Function,
  snapshot: Function,
};

Test Helper	description
listeners	[Object] A key/value map of active listeners (install/activate/fetch/etc).
trigger	[Function] Used to trigger active listeners (await self.trigger('install')).
snapshot	[Function] Used to generate a snapshot of the service worker internals (see below).

Snapshot Property	description
caches	[Object] A key/value map of current cache contents.
clients	[Array] A list of active clients.
notifications	[Array] A list of active notifications

Additionally we provide a fetch mock in service-worker-mock/fetch to easily get up and running (see Getting Started for example).

Getting Started

The service worker mock is best used by applying its result to the global scope, then calling require('../sw.js') with the path to your service worker file. The file will use the global mocks for things like adding event listeners.

const makeServiceWorkerEnv = require('service-worker-mock');
const makeFetchMock = require('service-worker-mock/fetch');

describe('Service worker', () => {
  beforeEach(() => {
    Object.assign(
      global,
      makeServiceWorkerEnv(),
      makeFetchMock(),
      // If you're using sinon ur similar you'd probably use below instead of makeFetchMock
      // fetch: sinon.stub().returns(Promise.resolve())
    );
    jest.resetModules();
  });
  it('should add listeners', () => {
    require('../sw.js');
    expect(self.listeners['install']).toBeDefined();
    expect(self.listeners['activate']).toBeDefined();
    expect(self.listeners['fetch']).toBeDefined();
  });
});

Use

The following is an example snippet derived from tests/basic.js. The test is based on the service worker example provided by Google. In it, we will verify that on activate, the service worker deletes old caches and creates the new one.

const makeServiceWorkerEnv = require('service-worker-mock');

describe('Service worker', () => {
  beforeEach(() => {
    Object.assign(global, makeServiceWorkerEnv());
    jest.resetModules();
  });
  
  it('should delete old caches on activate', async () => {
      require('../sw.js');

      // Create old cache
      await self.caches.open('OLD_CACHE');
      expect(self.snapshot().caches.OLD_CACHE).toBeDefined();

      // Activate and verify old cache is removed
      await self.trigger('activate');
      expect(self.snapshot().caches.OLD_CACHE).toBeUndefined();
      expect(self.snapshot().caches['precache-v1']).toBeDefined();
  });
});

License

MIT