Categories
e2e Testing

Playwright + Jest = 💖

We were looking at a possible replacement for our dated Protractor + Cucumber e2e testing framework. As we move away from Angular to React microapps we have found that Protractor doesn’t work very well/efficiently and cucumber isn’t giving us any benefits.

It was a good opportunity to do some research/tinkering to answer the question lingering in my mind: in 2020 what e2e testing tool would I use by default for a dynamic react based web application?

After some experimentation it came down to Puppeteer + Jest or Playwright + Jest. I’ll compare those in this post.

Why Jest?

As explained previously we don’t need a BDD framework, but we do need something that allows us to specify our tests, create assertions and run these tests (in parallel). Jest, particularly when using the Jest Circus test runner, seems the most mature tool in this regard in 2020. Whilst Jest is often associated with React as it handles the snapshot test results also, it doesn’t need to be used with React and it’s possible and easy to use it as a standalone Node.js testing library.

Parallel Support

Jest by default runs tests across files in parallel and uses the available resources to scale appropriately using processes/threads. I’ve found this particularly good as I write independent e2e tests which can scale through parallelism, and using Puppeteer and Playwright you can spawn new incognito browser contexts to run these.

Auto-Retry Support

Whilst I believe in writing deterministic e2e automated tests, since e2e tests are full-stack there are often external dependencies and services beyond our control (like a third party domain provider) and I’d rather prioritize test reliability over test perfection. With this mind I think it’s important to be able to automatically retry a single failing test scenario before failing a build, and the Jest Circus test runner supports this:

jest.retryTimes(1)

test('can wait for an element to appear', async () => {
  global.page = await pages.spawnPage()
  await nav.visitHomePage(global.page)
  await global.page.waitForSelector('#elementappearschild', { visible: true, timeout: 5000 })
}, jestTimeoutMS)

HTML Reports and Screenshots

Nice looking HTML reports are easy to achieve by using jest-stare and screenshots are easy to generate using Jest Circus hooks.

Playwright or Puppeteer?

I’m a fan of Puppeteer however Playwright is a much nicer browser automation library. Whilst it adds support for Firefox and Webkit, even if you’re running your e2e tests in one browser (Chromium) I’d still recommend Playwright over Puppeteer any day of the week. Here’s why:

Automatic Waiting

I’ve found the automatic waiting in Playwright just works™️ Especially when dealing with dynamically rendered react web apps I’ve found my Puppeteer code looks is full of page.waitFor calls to make it run reliably:

await page.waitFor('#loadedchild', { visible: true, timeout: 5000 })

Whilst this is occasionally necessary in Playwright (in particular waiting for an iFrame to switch into), I’ve found it’s almost never required which reminds me of good old Watir days.

Nicer API

Whilst the APIs are similar, Playwright is just nicer to use. Take grabbing some text from a div, in Puppeteer:

await page.goto(`${config.get('baseURL')}`)
await page.waitFor('#loadedchild', { visible: true, timeout: 5000 })
const element = await page.$('#loadedchild')
const text = await (await element.getProperty('textContent')).jsonValue()
expect(text).toBe('Loaded!')

In Playwright:

await page.goto(`${config.get('baseURL')}`)
const text = await page.textContent('#loadedchild')
expect(text).toBe('Loaded!')

Summary

If I was writing an e2e web testing framework from scratch in 2020 I would use Playwright + Jest. Playwright offers automatic waiting and a nice API, whilst Jest offers a solid runner with parallel support, automatic retries and the ability to easily generate HTML reports and capture screenshots.

I’ve created one repository for Playwright + Jest #
And another for Puppeteer + Jest to compare #

As an aside we put changing node libraries on hold for our e2e test framework and will look at some test infrastructure improvements instead.

Categories
Automated Acceptance Testing Automated Testing Selenium

Playing with Playwright

Playwright is a new browser automation library from Microsoft:

Playwright is a Node library to automate the Chromium, WebKit and Firefox browsers with a single API. It enables cross-browser web automation that is ever-green, capable, reliable and fast.

https://github.com/microsoft/playwright

I’m a big fan of Puppeteer, so this section in their FAQ stood out to me:

Puppeteer is a Node library which provides a high-level API to control Chrome or Chromium over the DevTools Protocol. Puppeteer project is active and is maintained by Google.

We are the same team that originally built Puppeteer at Google, but has since then moved on. Puppeteer proved that there is a lot of interest in the new generation of ever-green, capable and reliable automation drivers. With Playwright, we’d like to take it one step further and offer the same functionality for all the popular rendering engines. We’d like to see Playwright vendor-neutral and shared governed.

https://github.com/microsoft/playwright#q-how-does-playwright-relate-to-puppeteer

Playwright uses similar concepts to Puppeteer:

“Due to the similarity of the concepts and the APIs, migration between the two should be a mechanical task.”

https://github.com/microsoft/playwright#q-how-does-playwright-relate-to-puppeteer

Luckily I have a demo test suite written in Puppeteer which I have cloned and converted to use Playwright to see how it works, and compares.

Here are my thoughts:

I really, really like the BrowserContext concept

In Puppeteer, and WebDriverJs, you have Browsers and Pages. Each Page in a Browser share the state across the Browser, so to create isolated tests using the same Browser (to avoid the inefficiencies of spawning a Browser per test) you need custom code to delete all cookies and local storage between tests. Playwright solves this with the BrowserContext object which is a new incognito window where its pages are created: each test can use the same browser but a different BrowserContext. Super cool 👌

It automatically waits to click, and supports xpath expressions

Playwright automatically waits for elements to be available and visible before clicking, by default, and also has the same API for xpath expressions, which means this Puppeteer code:

await page.goto( `${ config.get( 'baseURL' )}` );
await page.waitForXPath( '//span[contains(., "Scissors")]' );
const elements = await page.$x( '//span[contains(., "Scissors")]' );
await elements[0].click();
await page.waitForXPath( '//div[contains(., "Scissors clicked!")]' );

becomes a lot cleaner:

await page.goto( `${ config.get( 'baseURL' )}` );
await page.click( '//span[contains(., "Scissors")]' );
await page.waitFor( '//div[contains(., "Scissors clicked!")]' );

It supports three “browsers” but not as you know them

Q: Does Playwright support new Microsoft Edge?

The new Microsoft Edge browser is based on Chromium, so Playwright supports it.

https://github.com/microsoft/playwright#q-does-playwright-support-new-microsoft-edge

Playwright supports three “browsers” but not as you know them. I’d say it supports three rendering engines (Chromium, WebKit & Gecko) rather than Browsers as you can only use the (somewhat modified) browsers that come bundled with Playwright over using an already installed browser on your operating system (like Selenium does). This makes it easier to ensure consistency of test runs since the library is bundled with the browsers, but there are some risks your tests could pass on the bundled browsers but fail on “real” browsers. I would say that the claim it supports running on Microsoft Edge is a little misleading.

I’m unsure of CircleCI Support for WebKit and Firefox

I was able to get my tests running against Chromium on CircleCI using the same configuration as Puppeteer, however I couldn’t get the WebKit or Firefox tests to run on CircleCI even when having the default CircleCI browsers installed. I didn’t want to invest the time, but it is probably due to some headless Linux dependencies missing which could be solved in the project config.

Conclusion

If the only thing Playwright did better than Puppeteer was also supporting WebKit and Gecko then I wouldn’t suggest using it over Puppeteer, since Puppeteer is closely aligned with Chromium, and I’m going to run my tests solely in Chrome/Chromium anyway. I don’t believe in running the same e2e tests in multiple browsers: the maintenance overhead outweighs the benefits in my experience.

However, Playwright offers a much nicer BrowserContext concept, and the xpath support is much nicer (although I rarely use xpath expressions anyway).

If anything I am hoping Puppeteer adds support for BrowserContexts – I’ve raised a feature request here so feel free to comment on it if you think it would be a good idea.

All the sample code is available here: https://github.com/alisterscott/playwright-demo