You are very welcome to contribute to the Bancho.js project! Most of the library is done by now -- but there are always improvements to be done. Feel free to open issues and discuss any of that over the dedicated Discord channel!
The public documentation is for the end-users; I recommend you to generate the private documentation for development purposes with npm run doc:dev to begin with.
To run the tests, you need to copy the example config.json.example file to config.json and edit your credentials. Execute them with npm run test.
After that, feel free to assign yourself to any issue and well... make magic happen!
I'll also require you to pass the CI tests. The irc test requires you to set up the IRC_USER, IRC_PASS, API_KEY (osu! API key) and USER_ID (osu! user id) secret variables in your project CI / CD settings, although I will be lenient on MRs not affecting the actual code on this test.
Feel free to create issues as well, and MR your work once you're finished.
You're very welcomed to write test units for the tests you write, when possible. Providing examples for new features is a plus.
Every examples and test units should always work at any commit in the project.