“Introduction to WPT” video transcript

Still image of the WPT logo. The song “My Luck” by Broke for Free (licensed under Creative Commons Attribution 3.0) plays in the background.

Hello, and welcome to the Web Platform Tests!

The goal of this project is to ensure that all web browsers present websites in exactly the way the authors intended.

But what is the web platform, exactly? You can think of it as having three main parts.

A top-down shot of a blank sheet of graph paper

First, there are the web browsers.

A hand places a paper cutout depicting a browser window in the lower-right corner of the sheet.

Applications like Firefox, Chrome, and Safari allow people to interact with pages and with each other.

Second, there are the web standards.

A hand places a paper cutout depicting a scroll of parchment paper in the lower-left corner of the sheet.

These documents define how the browsers are supposed to behave.

A screen recording of a web browser

https://platform.html5.org is entered into the location bar, and the browser loads the page.

That includes everything from how text is rendered to how augmented reality apps are built. Specifying it all takes a lot of work!

The browser clicks through to the Fetch standard and begins scrolling.

And as you might expect, the standards can get really complicated.

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A hand draws an arrow from the cutout of the scroll to the cutout of the browser window.

The people who build the browsers use the specifications as a blue print for their work. A shared set of generic instructions like these make it possible for people to choose between different browsers, but only if the browsers get it right.

A hand places a cutout representing a stack of papers on the top-center of the sheet and draws an arrow from that cutout to the cutout of the browser window.

To verify their work, the browser maintainers rely on the third part of the web platform: conformance tests.

A hand draws an arrow from the cutout of the scroll to the cutout of the tests.

We author tests to describe the same behavior as the standards, just formatted in a way that a computer can understand.

A hand draws an arrow from the cutout of the browser window to the cutout of the scroll.

In the process, the maintainers sometimes uncover problems in the design of the specifications, and they recommend changes to fix them.

A hand draws an arrow from the cutout of the tests to the cutout of the scroll.

Test authors also find and fix these so-called “spec bugs.”

A hand draws an arrow from the cutout of the browser window to the cutout of the tests.

…and as they implement the standards, the maintainers of each browser frequently write new tests that can be shared with the others.

This is how thousands of people coordinate to build the cohesive programming platform that we call the world wide web. The web-platform-tests project is one of the test suites that make this possible.

That’s pretty abstract, though! Let’s take a quick look at the tests themselves.

A screen recording of a web browser

http://wpt.live is entered into the location bar, and the browser loads the page.

The latest version of the tests is publicly hosted in executable form on the web at wpt.live.

The browser begins scrolling through the enormous list of directories.

There, were can navigate among all the tests for all the different web technologies.

Let’s take a look at a typical test.

The browser stops scrolling, and a mouse cursor clicks on fetch, then api, then headers, and finally headers-basic.html.

This test is written with the web-platform-tests’s testing framework, testharness.js. The test completes almost instantly, and testharness.js reports that this browser passes all but one subtest. To understand the failure, we can read the source code.

The mouse opens a context menu, selects “View Source”, and scrolls to the source of the failing test.

It looks like the failing subtest is for what happens when a Headers instance has a custom JavaScript iterator method. That’s a strange edge case, but it’s important for browsers to agree on every detail!

The mouse clicks on the browser’s “Back” button and then navigates through the directory structure to the test at css/css-transforms/transform-transformed-tr-contains-fixed-position.html. It displays text rendered at an angle.

Many tests don’t use testharness.js at all. Let’s take a look at a couple other test types.

When it comes to the visual appearance of a page, it can be hard to verify the intended behavior using JavaScript alone. For these situations, the web-platform-tests uses what’s known as a reftest.

Short for “reference test”, this type of test uses at least two different web pages.

The first page demonstrates the feature under test.

The mouse opens a context menu, selects “View Source”, and clicks on the href value for the matching reference. It looks identical to the previous page.

Inside of it, we’ll find a link to a second page. This second page is the reference page. It’s designed to use a different approach to produce the same output.

The mouse clicks back and forth between the browser tabs displaying the test page and the reference page.

When tests like these are run automatically, a computer verifies that screenshots of the two pages are identical.

The mouse clicks on the browser’s “Back” button and then navigates through the directory structure to the test at css/css-animations/animation-fill-mode-002-manual.html. The page includes the text, “Test passes if there is a filled color square with ‘Filler Text’, whose color gradually changes in the order: YELLOW to GREEN.” It also includes the described animated square.

Even with testharness.js and reftests, there are many web platform features that a computer can’t automatically verify. In cases like these, we fall back to using manual tests.

Manual tests can only be verified by a living, breathing human. They describe their expectations in plain English so that a human operator can easily determine whether the browser is behaving correctly.

https://web-platform-tests.org is entered into the location bar, and the browser loads the page.

You can read more about all the test types in the project documentation at web-platform-tests.org.

https://wpt.fyi is entered into the location bar, and the browser loads the page.

wpt.fyi is a great way to see how today’s browsers are performing on the web-platform-tests.

The browser scrolls to fetch, and a mouse cursor clicks on fetch, then api, then headers, and finally headers-basic.html.

Here, you’ll find all the same tests, just presented with the results from various browsers.

https://web-platform-tests.live/LICENSE.md is entered into the location bar, and the browser loads the page.

The web-platform-tests project is free and open source software. From bug reports to documentation improvements and brand new tests, we welcome all sorts of contributions from everyone.

https://github.com/web-platform-tests/wpt is entered into the location bar, and the browser loads the page.

To get involved, you can visit the project management website hosted on GitHub.com.

The browser navigates to the project’s “issues” list and filters the list for just the ones labeled as “good first issue.”

Some issues are more difficult than others, but many are perfect for people who are just getting started with the project. When we come across an issue like that, we label it as a “good first issue.”

https://lists.w3.org/Archives/Public/public-test-infra is entered into the location bar, and the browser loads the page.

You can also join the mailing list to receive e-mail with announcements and discussion about the project.

http://irc.w3.org/ is entered into the location bar, and the browser loads the page. web4all is entered as the Nickname, and #testing is entered as the channel name. A mouse clicks on the “Connect” button.

For more immediate communication, you can join the “testing” channel on the IRC server run by the W3C.

Return to the graph paper

A hand places a paper cutout depicting a human silhouette on the sheet. It then draws arrows from the new cutout to each of the three previously-introduced cutouts.

We’re looking forward to working with you!