https://github.blog/2022-02-02-build-ci-cd-pipeline-github-actions-four-steps/
Here’s a quick guide on the advantages of using GitHub Actions as your preferred CI/CD tool—and how to build a CI/CD pipeline with it.
I should get more into it, but one thing I am always not sure about: How do you test them? Have them on a separate branch (or even repo) and then trigger them? That seems a bit restrictive
Yes, usually most things can be tested on a different branch and just set the workflow to trigger from the branch rather than main. There are some cases where this doesn't work great, however, like testing triggers for pull requests, since then you have to have a 2nd branch to PR to the test branch.
There is also nectos/act, although I don't personally use it, I have heard it helps with faster development of workflows (and saves cost if you are not self hosting runners).