🚨 Pixel is currently an experimental proof of concept working towards becoming a more stable and useful solution. Only use it when you're feeling dangerous. 🚨

Pixel is a visual regression tool for MediaWiki developers/QA engineers that helps you replace manual testing with automated tests that catch web ui regressions before users see them. It currently integrates BackstopJS, MediaWiki-Docker, and Docker under the hood.

Pixel can also be used for accessibility regression testing using Pa11y and axe-core as the automated accessibility testing engine. Similar to visual regression testing, this makes it easier to see accessibility changes by comparing the results of accessibility tests between two patches.

Check out the hourly reports Pixel has generated at https://pixel.wmcloud.org which compare the latest release branch against master, and read T302246 for the motivation behind the tool.

First, clone the repo wherever you wish and cd into it:

git clone https://github.com/wikimedia/pixel.git && cd pixel

Pixel runs in multiple Docker containers to eliminate inconsistent rendering issues across environments. Please install Docker and make sure it is running prior to using Pixel.

Make sure you are running a compatible version of Node.js. The required version of Node is noted in the package.json file. We recommend using NVM for managing different versions of Node.js.

Finally, install the CLI dependency:

npm install

Running Pixel for the first time can take a long time (e.g. 5 minutes) as it downloads Docker images, clones MediaWiki core (> 2GB) and a number of extensions/skins. It will be much faster on subsequent runs as this data has already been downloaded.

Your workflow will usually involve the following ordered steps:

If you want to checkout the latest code in master or main from MediaWiki core and all of its installed extensions and skins and then take reference screenshots that your test screenshots (step 2) will be compared against, then:

./pixel.js reference

Or if you want the reference to be the latest release branch:

./pixel.js reference -b latest-release

Or if you want the reference to be a certain release branch:

./pixel.js reference -b origin/wmf/1.39.0-wmf.18

If you want to run the mobile visual regression test suite pass the --group mobile flag.

If you want to pull a change or multiple changes down from gerrit, take screenshots with these changes on top of master and then compare these screenshots against the reference screenshots, then

./pixel.js test -c Iff231a976c473217b0fa4da1aa9a8d1c2a1a19f2

Note that although change id Iff231a976c473217b0fa4da1aa9a8d1c2a1a19f2 has a Depends-On dependency, it is the only change that needs to be passed. Pixel will figure out and pull down the rest of the dependencies provided that it has the relevant repositories (set in repositories.json).

An HTML report of your test results with screenshots will be opened automatically on a Mac after the test completes. If you're not on a Mac, you can manually open the file at report/<name-of-test-group>/index.html.

Additionally, Pixel runs a server at http://localhost:3000 (default) which can be used to interact with/debug the same server that the tests use.

If you want to run the mobile visual regression test suite pass the --group mobile flag.

Pixel can also compare accessibility errors between a reference and test patch. In order to use this feature, just add the --a11y flag when running reference and test commands.

./pixel.js reference -b latest-release --a11y
./pixel.js test -c Iff231a976c473217b0fa4da1aa9a8d1c2a1a19f2 --a11y

The HTML report of the test results can be found at report-a11y/<name-of-test-group>/<name-of-test>.html.

If you want to stop all of Pixel's services, run:

./pixel.js stop

Updating Pixel to the latest version can be done with the following command when you are on the main branch:

./pixel.js update

This command will git pull the latest code from the main branch and destroy all Docker containers, volumes, and networks associated with Pixel. It will also rebuild any Docker images that need to be rebuilt to ensure that it is using the latest database seed data and code.

Sometimes after making MediaWiki code changes, database changes, or having issues with the containers you just want to throw away everything and start Pixel with a clean slate. To do that, run:

./pixel.js clean

You can also reset Pixel's database to its original state with:

./pixel.js reset-db

All tests are located in config files in the root directory (e.g. configDesktop.js, configMobile.js, configEcho.js, etc).

For example, to test a new url in the mobile group:

1. Add a new object to the tests array in configMobile.js with the name of your test and its url path:

{
	label: "<descriptive-name-of-your-test>",
	path: "<url-path-of-page>"
}

2. Run the tests with:

./pixel.js reference -g mobile -b latest-release
./pixel.js test -g mobile -b latest-release

This should always pass if the tests are deterministic as it is testing the same code in MediaWiki (no changes).

For more info on how to change or add test config, please refer to the BackstopJS README.

There are several groups of tests that can be run:

UI checks on the mobile and desktop site limited to the Echo (notifications feature).

UI checks on the desktop site.

UI checks on the desktop site with various feature flags enabled. Feature flags must be manually updated inside configDesktopDev.js.

UI checks on the mobile site.

All mediawiki config is in LocalSettings.php and can be changed. For example, perhaps you are working on a new feature in the Vector skin that is feature flagged and want to enable it.

1. Edit LocalSettings.php
2. Check that your config is usable at localhost:3000
3. Commit these changes and open a pull request in this repo with these changes

Pixel gets its seed data from MariaDB backups hosted at https://github.com/wikimedia/pixel-seed-data.

Please follow the README.md in that repo for step-by-step instructions on how to make database changes.

Pixel ships with a number of MediaWiki extensions and skins already installed. Please reference the repositories.json file to see a list of these.

To add a skin or extension that isn't currently supported:

1. Add it to the repositories.json file
2. Make Pixel rebuild its code volume by running ./pixel.js clean. This will destroy every container, image, volume, network associated with Pixel so they can be rebuilt.
3. Configure the extension or skin in LocalSettings.php.
4. Run ./pixel.js reference to rebuild everything. This will also run the maintenance/update.php script which executes any needed database schema changes. This will take awhile as Mediawiki core, extensions, and skins get downloaded again.
5. Check that your extension or skin is usable at localhost:3000
6. If there were any database changes involved, you'll need to update the seed data that is shared amongst users of Pixel. To do this, please follow steps 3 through 9 on the Pixel seed data repo.
7. Commit these changes and open a pull request in this repo with these changes

Please file all bugs, requests, and issues on the web team's visual regression phabricator board

Future plans can be seen by visiting the web team's visual regression phabricator board under the "Roadmap (Epics)" column.