For the gjs test plan, it looks broadly sane.
Again, I’d be a fan of a test plan with more structure than “make sure GNOME Shell still works correctly” - for example, is it worth checking the journal to identify any new warnings generated to check that they’re harmless?
Would it additionally be worth checking that the supported Shell extensions still work? They obviously have the potential to be affected by any change in the JS environment, but it’s not clear to me how likely they are to hit things that the default Shell doesn’t, so I don’t know if testing them is worthwhile.