This article is based on my opening keynote address for Front End Test Fest 2022.
In the featured image for this article, you see a beautiful front end. It’s probably not the kind of “front end” you expected. It’s the front end of a 1974 Volkswagen Karmann Ghia. The Karmann Ghia was known as the “poor man’s Porsche.” It’s a very special car. It was actually a collaboration project between Wilhelm Karmann, a German automobile manufacturer, and Carrozzeria Ghia, an Italian automobile designer. Ghia designed the body as a work of art, and Karmann put it on the tried-and-true platform of the classic Volkswagen Beetle. When the Volkswagen executives saw it, they couldn’t say no to mass production.
The Karmann Ghia is a perfect symbol of the state of web development today. We strive to make beautiful front ends with reliable platforms supporting them on the back end. Collaboration from both sides is key to success, but what people remember most is the experience they have with your apps. My mom drove a Karmann Ghia like this when she was a teenager, and to this day she still talks about the good times she had with it.
Good quality, design, and experience are indispensable aspects of front ends – whether for classic cars or for the Web. In this article, I’ll share seven major trends I see in front end web testing. While there’s a lot of cool new things happening, I want y’all to keep in mind one main thing: tools and technologies may change, but the fundamentals of testing remain the same. Testing is interaction plus verification. Tests reveal the truth about our code and our features. We do testing as part of development to gather fast feedback for fixes and improvements. All the trends I will share today are rooted in these principles. With good testing, you can make sure your apps will look visually perfect, just like… you know.
#1. End-to-end testing
Here’s our first trend: End-to-end testing has become a three-way battle. For clarity, when I say “end-to-end” testing, I mean black-box test automation that interacts with a live web app in an active browser.
Over the years, though, Selenium has received a lot of criticism. Selenium WebDriver is a low-level protocol. It does not handle waiting automatically, leading many folks to unknowingly write flaky scripts. It requires clunky setup since WebDriver executables must be separately installed. Many developers dislike Selenium because coding with it requires a separate workflow or state of mind from the main apps they are developing.
Cypress was the answer to Selenium’s shortcomings. It aimed to be a modern framework with excellent developer experience, and in a few short years, it quickly became the darling test tool for front end developers. Cypress tests run in the browser side-by-side with the app under test. The syntax is super concise. There’s automatic waiting, meaning less flakiness. There’s visual tracing. There’s API calls. It’s nice. And it took a big chomp out of Selenium’s market share.
Enter Playwright, the new open source test framework from Microsoft. Playwright is the spiritual successor to Puppeteer. It boasts the wide browser and language compatibility of Selenium with the refined developer experience of Cypress. It even has a code generator to help write tests. Plus, Playwright is fast – multiple times faster than Selenium or Cypress.
Playwright is still a newcomer, and it doesn’t yet have the footprint of the other tools. Some folks might be cautious that it uses browser projects instead of stock browsers. Nevertheless, it’s growing fast, and it could be a major contender for the #1 title. In Applitools’ recent Let The Code Speak code battles, Playwright handily beat out both Selenium and Cypress.
All these are good tools to choose (except Protractor). They can handle any kind of web app that you’re building. If you want to learn more about them, Test Automation University has courses for each.
#2. Component testing
End-to-end testing isn’t the only type of testing a team can or should do. Component testing is on the rise because components are on the rise! Many teams now build shareable component libraries to enforce consistency in their web design and to avoid code duplication. Each component is like a “unit of user interface.” Not only do they make development easier, they also make testing easier.
Component testing is distinct from unit testing. A unit test interacts directly with code. It calls a function or method and verifies its outcomes. Since components are inherently visual, they need to be rendered in the browser for proper testing. They might have multiple behaviors, or they may even trigger API calls. However, they can be tested in isolation of other components, so individually, they don’t need full end-to-end tests. That’s why, from a front end perspective, component testing is the new integration testing.
Storybook is a very popular tool for building and testing components in isolation. In Storybook, each component has a set of stories that denote how that component looks and behaves. While developing components, you can render them in the Storybook viewer. You can then manually test the component by interacting with them or changing their settings. Applitools also provides an SDK for automatically running visual tests against a Storybook library.
Cypress is also entering the component testing game. On June 1, 2022, Cypress released version 10, which included component testing support. This is a huge step forward. Before, folks would need to cobble together their own component test framework, usually as an extension of a unit test project or an end-to-end test project. Many solutions just ran automated component tests purely as Node.js processes without any browser component. Now, Cypress makes it natural to exercise component behaviors individually yet visually.
I love this quote from Cypress about their approach to component testing:
This quote hits on something big. So many automated tests fail to interact with apps like real users. They hinge on things like IDs, CSS selectors, and XPaths. They make minimal checks like appearance of certain elements or text. Pages could be completely broken, but automated tests could still pass.
#3. Visual testing
We really want the best of both worlds: the simplicity and sensibility of manual testing with the speed and scalability of automated testing. Historically, this has been a painful tradeoff. Most teams struggle to decide what to automate, what to check manually, and what to skip. I think there is tremendous opportunity in bridging the gap. Modern tools should help us automate human-like sensibilities into our tests, not merely fire events on a page.
That’s why visual testing has become indispensable for front end testing. Web apps are visual encounters. Visuals are the DNA of user experience. Functionality alone is insufficient. Users expect to be wowed. As app creators, we need to make sure those vital visuals are tested. Heaven forbid a button goes missing or our CSS goes sideways. And since we live in a world of continuous development and delivery, we need those visual checkpoints happening continuously at scale. Real human eyes are just too slow.
For example, I could have a login page that has an original version (left) and a changed version (right):
Visual testing tools alert you to meaningful changes and make it easy to compare them side-by-side. They catch things you might miss. Plus, they run just like any other automated test suite. Visual testing was tough in the past because tools merely did pixel-to-pixel comparisons, which generated lots of noise for small changes and environmental differences. Now, with a tool like Applitools Visual AI, visual comparisons accurately pinpoint the changes that matter.
Test automation needs to check visuals these days. Traditional scripts interact with only the basic bones of the page. You could break the layout and remove all styling like this, and there’s a good chance a traditional automated test would still pass:
With visual testing techniques, you can also rethink how you approach cross-browser and cross-device testing. Instead of rerunning full tests against every browser configuration you need, you can run them once and then simply re-render the visual snapshots they capture against different browsers to verify the visuals. You can do this even for browsers that the test framework doesn’t natively support! For example, using a platform like Applitools Ultrafast Test Cloud, you could run Cypress tests against Electron in CI and then perform visual checks in the Cloud against Safari and Internet Explorer, among other browsers. This style of cross-platform testing is faster, more reliable, and less expensive than traditional ways.
#4. Performance testing
Functionality isn’t the only aspect of quality that matters. Performance can make or break user experience. Most people expect any given page to load in a second or two. Back in 2016, Google discovered that half of all people leave a site if it takes longer than 3 seconds to load. As an industry, we’ve put in so much work to make the front end faster. Modern techniques like server-side rendering, hydration, and bloat reduction all aim to improve response times. It’s important to test the performance of our pages to make sure the user experience is tight.
Thankfully, performance testing is easier than ever before. There’s no excuse for not testing performance when it is so vital to success. There are many great ways to get started.
The simplest approach is right in your browser. You can profile any site with Chrome DevTools. Just right click the page, select “Inspect,” and switch to the Performance tab. Then start the profiler and start interacting with the page. Chrome DevTools will capture full metrics as a visual time series so you can explore exactly what happens as you interact with the page. You can also flip over to the Network tab to look for any API calls that take too long. If you want to learn more about this type of performance analysis, Test Automation University offers a course entitled Tools and Techniques for Performance and Load Testing by Amber Race. Amber shows how to get the most value out of that Performance tab.
Another nifty tool that’s also available in Chrome DevTools is Google Lighthouse. Lighthouse is a website auditor. It scores how well your site performs for performance, accessibility, progressive web apps, SEO, and more. It will also provide recommendations for how to improve your scores right within its reports. You can run Lighthouse from the command line or as a Node module instead of from Chrome DevTools as well.
Using Chrome DevTools manually for one-off checks or exploratory testing is helpful, but regular testing needs automation. One really cool way to automate performance checks is using Playwright, the end-to-end test framework I mentioned earlier. In Playwright, you can create a Chrome DevTools Protocol session and gather all the metrics you want. You can do other cool things with profiling and interception. It’s like a backdoor into the browser. Best of all, you could gather these metrics together with functional testing! One framework can meet the needs of both functional and performance test automation.
John Hill is a trailblazer in this space. He’s currently doing this as part of the Open MCT project. He’s the one who showed me how to automate performance tests with Playwright! If you want to learn more, check out this talk he gave recently on performance testing with Playwright, as well as his js-perf-toolkit project on GitHub.
Below is an example snippet I copied from js-perf-toolkit showing how to gather performance metrics using Playwright:
const client = await page.context().newCDPSession(page); await client.send('Performance.enable'); await page.goto('https://www.google.com/'); await page.click('[aria-label="Search"]'); await page.fill('[aria-label="Search"]', 'playwright'); await Promise.all([ page.waitForNavigation(), page.press('[aria-label="Search"]', 'Enter') ]); let perfMetrics = await client.send('Performance.getMetrics'); console.log( perfMetrics.metrics );
#5. Machine learning models
There’s another curve ball when testing websites: what about machine learning models? For example, whenever you shop at an online store, the bottom of almost every product page has a list of recommendations for similar or complementary products. For example, when I searched Amazon for the latest Pokémon video game, Amazon recommended other games and toys:
Recommendation systems like this might be hard-coded for small stores, but large retailers like Amazon and Walmart use machine learning models to back up their recommendations. Models like this are notoriously difficult to test. How do we know if a recommendation is “good” or “bad”? How do I know if folks who like Pokémon would be enticed to buy a Kirby game or a Zelda game? Lousy recommendations are a lost business opportunity. Other models could have more serious consequences, like introducing harmful biases that affect users.
Machine learning models need separate approaches to testing. It might be tempting to skip data validation because it’s harder than basic functional testing, but that’s a risk not worth taking. To do testing right, separate the functional correctness of the frontend from the validity of data given to it. For example, we could provide mocked data for product recommendations so that tests would have consistent outcomes for verifying visuals. Then, we could test the recommendation system apart from the UI to make sure its answers seem correct. Separating these testing concerns makes each type of test more helpful in figuring out bugs. It also makes machine learning models faster to test, since testers or scripts don’t need to navigate a UI just to exercise them.
If you want to learn more about testing machine learning courses, Carlos Kidman created an excellent course all about it on Test Automation University named Intro to Testing Machine Learning Models. In his course, Carlos shows how to test models for adversarial attacks, behavioral aspects, and unfair biases.
Below is an example snippet of HTML code with HTMX attributes for posting a click and showing the response:
<script src="https://firstname.lastname@example.org"></script> <!-- have a button POST a click via AJAX --> <button hx-post="/clicked" hx-swap="outerHTML"> Click Me </button>
#7. Autonomous testing
Finally, there is one more trend I want to share, and this one is more about the future than the present: autonomous testing is coming. Ironically, today’s automated testing is still manually-intensive. Someone needs to figure out features, write down the test steps, develop the scripts, and maintain them when they inevitably break. Visual testing makes verification autonomous because assertions don’t need explicit code, but figuring out the right interactions to exercise features is still a hard problem.
I think the next big advancement for testing and automation will be autonomous testing: tools that autonomously look at an app, figure out what tests should be run, and then run those tests automatically. The key to making this work will be machine learning algorithms that can learn the context of the apps they target for testing. Human testers will need to work together with these tools to make them truly effective. For example, one type of tool could be a test recommendation engine that proposes tests for an app, and the human tester could pick the ones to run.
Autonomous testing will greatly simplify testing. It will make developers and testers far more productive. As an industry, we aren’t there yet, but it’s coming, and I think it’s coming soon. I delivered a keynote address on this topic at Future of Testing: Frameworks 2022:
There’s lots of exciting stuff happening in the world of the front end. As I said before, tools and technologies may change, but fundamentals remain the same. Each of these trends is rooted in tried-and-true principles of testing. They remind us that software quality is a multifaceted challenge, and the best strategy is the one that provides the most value for your project.
So, what do you think? Did I hit all the major front end trends? Did I miss anything? Let me know in the comments!