BabySteps with tests on headless browser

IntersectionObserver.puppeteer.test.js

import puppeteer from 'puppeteer'

const url = 'http://localhost/'

let browser

describe('It checks that Intersection Observer is available', () => {
  beforeAll(async () => {
    browser = await puppeteer.launch({
      headless: true,
      slowMo: 80,
      args: [`--window-size:800,600`]
    })
    const page = await browser.newPage()
    await page.setViewport({ width: 800, height: 600})
  })

  afterAll(async () => {
    browser.close()
  })

  test('verifies existence of global variables', async () => {
    const page = await browser.newPage()

    await page.goto(url)

    const title = await page.title()
    const aWindowHandle = await page.evaluateHandle(() => window)

    expect(aWindowHandle).toBeDefined()

    const io = await page.evaluate(() => window.IntersectionObserver)
    expect(io).toBeDefined()
  })
})