Should test configuration `setupTests.{ts,js}` be per-application? Should tests be run globally against the project or are they run against specific applications?

Should test configuration setupTests.{ts,js} be per-application?

I noticed that CRA would only load the setupTests.{js,ts} of one application and amended our test configuration to load the test configuration of each application. This was done because I didn’t want any one application to be special-cased as containing the configuration for all other application’s tests, however since all of the setupTest files are loaded when the tests are run, it means that if you make a change to the configuration you do so for everybody. There could be conflicts.

Should tests be run globally against the project or will they be run against specific applications?

I thought the former was what we were trying to achieve, and if that’s the case and presuming that others agree that distributing configuration across a repository is a Bad Idea™, then it seems like a good idea to move to having a single setupTests.{js,ts} at the root of the modular project.

However, it’s also possible that every application could have their own modular test [app-name] command that they run. This would certainly be helpful when migrating applications with differing test configuration into a single repository. Additionally:

• Are there long-term benefits to making modular test work this way?
• What about packages and widgets that aren’t part of the application, but are depended upon by it – how would we know that the tests for these should be run with a particular application’s modular test [app-name] command and that its setupTests configuration will run these correctly?
• When you make a change to a design system that affects all application’s within a single repository, what test command would you use to make sure nothing is broken – presumably there would still need to be a modular test command without an [app-name] argument that can run all of the tests and that would need to be configured with every single setupTests.{ts,js} within the repository?

See also: https://github.com/jpmorganchase/modular/pull/100#discussion_r490486855

[threepointone]

Honestly, maybe that’s a good place to draw a line in the sand. They’re welcome to unmock/remock in individual files, and if it’s a lot, they can codemod the boilerplate. Let’s strive for a singular setupTests for now, and play it by ear. Should be an enlightening exercise.

[sebinsua]

I’ll make this change this week.

What I’m tempted to do is to leave the logic which loads packages/*/src/setupTest.{js,ts} since this is CRA-like (and their docs would tell people to put setupTests files here – the other possibility I guess is that I could console.warn about this). But, importantly, I would copy the default setupTests.{js,ts} file into the modular root by default and document that this is the correct location.