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Using with puppeteer

With the Global Setup/Teardown and Async Test Environment APIs, Jest can work smoothly with puppeteer.

Generating code coverage for test files using Puppeteer is currently not possible if your test uses page.$eval, page.$$eval or page.evaluate as the passed function is executed outside of Jest's scope. Check out issue #7962 on GitHub for a workaround.

Un ejemplo de A jest-puppeteer

La idea básica es:

1. iniciar y archivar el punto final websocket de puppeteer con configuración global
2. conectarse a puppeteer desde cada entorno de prueba
3. cerrar puppeteer con Global Teardown

Aquí hay un ejemplo del script GlobalSetup

// setup.js
const fs = require('fs');
const os = require('os');
const path = require('path');
const mkdirp = require('mkdirp');
const puppeteer = require('puppeteer');

const DIR = path.join(os.tmpdir(), 'jest_puppeteer_global_setup');

module.exports = async function () {
  const browser = await puppeteer.launch();
  // store the browser instance so we can teardown it later
  // this global is only available in the teardown but not in TestEnvironments
  global.__BROWSER_GLOBAL__ = browser;

  // use the file system to expose the wsEndpoint for TestEnvironments
  mkdirp.sync(DIR);
  fs.writeFileSync(path.join(DIR, 'wsEndpoint'), browser.wsEndpoint());
};

Entonces necesitamos un entorno de prueba personalizado para puppeteer

// puppeteer_environment.js
const fs = require('fs');
const os = require('os');
const path = require('path');
const puppeteer = require('puppeteer');
const NodeEnvironment = require('jest-environment-node');

const DIR = path.join(os.tmpdir(), 'jest_puppeteer_global_setup');

class PuppeteerEnvironment extends NodeEnvironment {
  constructor(config) {
    super(config);
  }

  async setup() {
    await super.setup();
    // get the wsEndpoint
    const wsEndpoint = fs.readFileSync(path.join(DIR, 'wsEndpoint'), 'utf8');
    if (!wsEndpoint) {
      throw new Error('wsEndpoint not found');
    }

    // connect to puppeteer
    this.global.__BROWSER__ = await puppeteer.connect({
      browserWSEndpoint: wsEndpoint,
    });
  }

  async teardown() {
    await super.teardown();
  }

  runScript(script) {
    return super.runScript(script);
  }
}

module.exports = PuppeteerEnvironment;

Finally, we can close the puppeteer instance and clean-up the file

// teardown.js
const os = require('os');
const path = require('path');
const rimraf = require('rimraf');

const DIR = path.join(os.tmpdir(), 'jest_puppeteer_global_setup');
module.exports = async function () {
  // close the browser instance
  await global.__BROWSER_GLOBAL__.close();

  // clean-up the wsEndpoint file
  rimraf.sync(DIR);
};

Con todo lo configurado, ahora podemos escribir nuestras pruebas de esta manera:

// test.js
const timeout = 5000;

describe(
  '/ (Home Page)',
  () => {
    let page;
    beforeAll(async () => {
      page = await global.__BROWSER__.newPage();
      await page.goto('https://google.com');
    }, timeout);

    it('should load without error', async () => {
      const text = await page.evaluate(() => document.body.textContent);
      expect(text).toContain('google');
    });
  },
  timeout,
);

Finally, set jest.config.js to read from these files. (The jest-puppeteer preset does something like this under the hood.)

module.exports = {
  globalSetup: './setup.js',
  globalTeardown: './teardown.js',
  testEnvironment: './puppeteer_environment.js',
};

Here's the code of full working example.