Isn't that the point of test events though?
It is mate but knowing UEFA, they simply won’t risk an opening game happening in one of their comps, especially a CL q-f.
Imagine the barriers conk out, no one can get in & the game gets postponed. It is highly unlikely to happen but they will highlight a worst-case scenario, regardless of test events.
I don’t agree by the way but, playing devils advocate, I can’t see the European governing body taking any gambles.