How do you test multiplayer (team) bosses? Does it take more than one person, or do you run invincibility cheats and just solo it? Do you even do regular playthrough of a boss as a QA, the way players would fight it? Or do just just script it to check the phasing and boss states etc?
Cheers for doing the Q&A.
There's a distinction to be made here between testing for QA purposes, and playtesting for playability, for example.
In terms of QA testing, typically mechanics and structures are tested as a solo player or using multiple accounts and checking to see if you get expected results from whatever you're doing. Checking to see what occurs when you do an action or that numbers look correct and so on.
When it comes to playtesting, we'll group up with others and try to take the boss on as players would. This is done pretty regularly, Raksha, Rex Matriarchs, and all 4 fronts of EGWD had a wider team playtest once a week during development to ensure it was getting the attention it needed at all times throughout development. In the past i know we've even brought players in to try them out, and sometimes even outside of team playtest folks such as the combat council will try taking group bosses on together.