////Unless he has a twisted streak, I’ve never understood why a creator would feel the need to test people when he already knows the outcome -/////
You are right that why would a creator who knows the outcome would test people? Reason is very simple. Creator knows the outcome but people do not. There is a hadith explaining but I would not give you hadith because you do not like so therefore I would give you an example from your and our own life.
Suppose you are a teacher who knows which of his/her students would pass the exams and which ones would fail. Now you have two options,
1 – Because you know so you might say no test and I know what the result would have been had I given you a test and therefore A, B, D pass the test and C fails it.
Now the problem would be that A,B and D would be laughing trusting the judgment of the teacher (or creator) but what about C? He/she might say that had I been given the test I might have passed it and therefore it is unjust. And to be honest he/she has good point.
Or let’s see the second option creator (or teacher) have,
2 – Teacher knows what would happen if he had taken the step 1, and therefore he/she lets the test happen and after that the result is still same as in scenario 1. A,B and D pass it and C fails it.
Now you tell me, would C has an excuse that had he/she been given an opportunity he/she might have passed the test?
Now apply above example on yourself and see where you stand, are you A, B, C or D?