So our development process is we create content in version controlled parallel streams (whether that's a whole project like the Nodon front, a biggie expansion like Menaphos, or isolated patches).
That in-development layer could be thought of as WIP (Work In Progress).
Because historically all developers worked in one dev "stream" called WIP (before we had parallel Perforce VC streams). Which was as crazy as it sounds and didn't scale particularly well as we hired more devs.
Quality Assurance testers attached to those projects test what content/tech developers create in those streams when they're functional. Historically known as "WIP testing".
That's also where we peer code review and implement feedback.
The dev adds release notes to the JIRA ticket that tracks that issue, attaches repro steps and any debugprocs or helpers they've created to assist in testing, and address any bugs or feedback raised by QA or stakeholders.
Then, once QA have confirmed the acceptance criteria for the issue have been met, they either change the JIRA status to Done (in cases where the whole project stream is going to be uploaded to RC in time for a scheduled release date) or Awaiting Copy if it's an isolated patch that could be pulled into an RC build whenever the RC team has capacity.
So, that gets us to Release Candidate testing.
Near the start of a week (shortly after making that Monday's game update happen), Mod Easty (or a similarly wizardly upload manager - Mod Helen is growing well versed in the dark arts, for example) copies changelists for the done project streams and/or patches awaiting copy in priority order into a Release Candidate stream (live + the new stuff that's a candidate for release), and resolves any merge conflicts.
Then RC QA (Release Candidate Quality Assurance) tests each of the submissions to ensure their acceptance criteria are still met after the upload manager's merged them together and are still working as intended without conflicts.
Then on Monday the upload manager sacrifices as many mammals necessary to deploy the new build to live, refresh all the RuneScape servers across the world, and propagate a weekly game update to all of our players.
There's a lot of other steps in the process - localisation, audio, news posts, login messages, livestream notifications, creative services, promotional material, etc - but that's a greatly simplified summary of the core development flow from WIP to RC to live. And we do that almost every week of every month of every year.
I'll answer your other question in a second post, because this is already dangerously huge!