Note that package-lock.json needs to be in the repo for the GitHub Actions npm cache to properly work. It will reuse the npm cache if package-lock.json didn't change.

codecov upload should work, but I can't test it on my fork. It finds the tests/coverage/lcov.info file and try to upload it to codecov, but I get a 404 there.

I set up testing only on chrome, but you can enable it for firefox if you want, it's just commented.

I enabled the tests on firefox, it seems fine. You'll see if there are some tests that are randomly failing on Firefox or not later on other PRs. If there is an issue with it, just comment it.
The CI is actually already running on this PR. \o/
https://github.com/aframevr/aframe/runs/7859579555?check_suite_focus=true

You can merge this PR and close the first one, or merge the first one, then I rebase this one and you merge, as you wish.

Compared to the previous travis config, I added a check for the minified build that runs npm run dist.
In travis, TEST_SUITE=unit was set but this variable is not used in any part of the code, I think it was to parallelize the tests but from travis documentation I think it was misused or didn't have an effect at all. Anyway I didn't use it in the new CI.

codecov upload is working, it uploaded the results from this PR:
https://codecov.io/github/aframevr/aframe/commit/057863548eea0358f0b1a0307a1fb67bcd4c4f18

It needs rebase!

I rebased.

About putting package-lock.json in the repo, mainly to have the npm cache in CI, it may add a burden to you to update the file from time to time to keep up to date dependencies for patch versions of some of the dependencies.
Having the .npm folder cached in CI means reducing the "Install dependencies" step from 2m51 to 1m18.
I can remove it.

done, good to merge

Thanks so much! This is great work. Tests don't get much love. I let them rotten a little bit 😄