[Localization] Add test cases

[mnajdova]

Summary 💡

Recently with #22293 I broke the locales, but no tests caught this. We should cover the localization with tests, so this won't happen again.

[Avi98]

hi @mnajdova , I really want to learn how tests are implemented in Material-UI. Can I take this issue

[eps1lon]

hi @mnajdova , I really want to learn how tests are implemented in Material-UI. Can I take this issue

Feel free to work on it. I'm assigning you for bookkeeping purposes only. If you decide to no longer work on this issue please leave a message so that other people can take over.

https://github.com/mui-org/material-ui/blob/next/test/README.md might be a good starting point to learn about our testing approach and infrastructure.

[Avi98]

hi @mnajdova, I tried to go through the pull request #22293 but could not figure out what all things I need to cover in the tests. It would be great if someone could help me understand what should be the scope of tests.

[Avi98]

Unassign it from me as I don't have enough clarity.

[reedanders]

hi @mnajdova, I'd like to close this up, but I would like to certain of the case where localization broke in #22293.

Can you confirm this is the failure you'd like to test for? #22293 (comment). Specifically, changing localization to https://deploy-preview-22293--material-ui.netlify.app/zh/customization/density/#main-content results in a 404 error.