DigitalOcean and Github for the last few years have put together an event called "Hactoberfest" where you can sign up and get a shirt after 5 pull requests.
I've made a repo to build out tests for all of ServiceNow's tool to help everyone get there.
Check it out on Github.
To contribute you just need a personal developer instance and the drive to make a test and / or suite to test some OOB functionality.
All tests should be self contained. What do I mean by that? Well, anything you reference in the test may need to be created like the user you want to impersonate, and their group memberships/roles.
I do intend on making a custom test as part of this to make the
generation of these artifacts easier but I am still learning how the
code works for those tests.
However this post at least is a decent example of someone doing a custom test step.