I found this topic about testing plugins (automatically), but haven’t come across any mentioning how to test themes or theme components. Are there any examples of how to use QUnit (or similar) with themes?
AI-generated summary
The discussion revolves around testing themes or theme components in Discourse. agmontpetit initially asked about automated testing using QUnit, but awesomerobot mentioned that it’s not currently possible. david suggested that adding support for QUnit tests in themes/components is possible but would require significant work.
The conversation highlights the trade-offs between using theme components and plugins, with eviltrout noting that theme components are easy to deploy but often lack testing. sam proposed considering this issue when working on the Ember CLI, and david suggested using the theme-cli to run QUnit tests inside a Docker image.
However, pmusaraj revealed that support for theme tests was added in mid-2021, allowing tests to be run in a local environment or production site. The discussion also touched on the possibility of extending this to testing JavaScript in plugins, with pmusaraj mentioning that running tests in production is currently only available for themes, but merefield suggested that the goal should be to run tests in CI on GitHub for both theme and plugin JavaScript.
You can add it to a user selectable theme or use the test link on the theme admin page.
Sorry, I meant automated testing – I will amend my previous post. I was thinking of something like QUnit that some plugins already use.
No, it’s not possible to add QUnit tests to themes/components at the moment…
@david how possible would it be possible to add support for a /test folder like plugins? we’d also have to enable the theme when the tests are run because the core tests run without any theme, right?
Certainly possible, but will need some work. Right now all the theme javascript files are bundled together into one file. We would need to make sure tests are put in a new, separate bundle, so that they don’t get served to regular visitors. And then once that’s done, make a way to run qunit tests for a single theme.
The other thing to consider is that we don’t make the /qunit route available on production servers. Since themes are often developed on production servers, we may need to rethink this 
This is one of the major downsides of theme components in my opinion. They are super easy to deploy which is fantastic, but testing often gets put aside.
If I understand correctly, anything that can be done with a theme component can be done with a plugin. The former is easier to deploy, while the latter allows testing.
Yes that is generally accurate. It ends up being a trade off in terms of what you are customising. For example adding a custom stylesheet probably couldn’t be tested even in a plugin. Adding custom javascript controls and widgets is where things become questionable.
I feel like we should consider this issue when we do the ember cli work. There is nothing impossible about having some sort of test runner for themes, and we could ship some of the basics in the discourse-theme gem to set up local testing using ember cli.
Running theme tests would require a full installation of Discourse though, right? There are so many interdependencies I don’t think we could test themes independently
Maybe the theme-cli could have some logic to pull the discourse_dev docker image and run qunit tests inside that?
The whole idea with ember cli is that we are cleanly splitting server from client. We could ship enough of the JS side of things to test the client without running a rails server. You would still need node and ember cli installed for sure, but you may get away without installing a full Discourse stack including Redis and Postgres.
It might be tricky but something we can definitely keep in mind.
We now support tests in themes (late update, support for theme tests was added in mid-2021). You can head to /theme-qunit in your local environment or your production site, and any installed themes/components that have tests will be listed there. See Discourse Tab Bar for Mobile or Tag icons component for examples.
This is great. Will this extend to testing javascript in Plugins?
Do you mean being able to run tests in production? That’s for themes only at this point.
(Locally you can run plugin JS tests, of course.)
I think goal would be to be able to run them in CI on GitHub as we currently can with specs (both Theme.and Plugin JS)?
Yes, we run tests in CI for all official plugins.