Most ad testing changes everything at once and teaches you nothing. The money is in the first three seconds.
Running three ads with different hooks, different edits and different offers tells you which one won — and nothing about why.
Test one thing at a time: the opening frame, the first line, the pace of the first cut, whether a face appears. Those move watch-time, and watch-time moves everything else.
Then move the budget fast. Keeping an expensive ad alive because it was expensive to make is the quickest way to waste a good production budget.