There is a big difference between getting a solid idea for what will happen before testing and literally being able to see the future as clearly as the present. If a software developer literally can see the future and already knows what error will occur if he tries to run the code then he would not run it. Or to use the engineer example, let’s say someone is creating a humanoid robot which is still in the early phases of development but the creator believes that it has just reached a point where it is able to sort of balance for a second. First of all, he can’t KNOW that it’s at that point without testing. And even if he has a very good idea that it is probably at that point he certainly won’t know exactly how it is going to fail eventually during the test. If the designer is all-knowing then he would literally know every force that is applied to the robot as it attempts to stand, the exact way that it will stumble down to the minutiae, etc. There is no reason, not for fun, not for learning, literally no logical reason to run that test in that case.

I also agree that religion is a bunch of BS but if I were to try to come up with a justification to the question of why an all-knowing creator would test their creation, I would say that it isn’t for the sake of the creator but rather to teach the person they are testing about themselves or some BS like that. That being said, I think there are many many ways that you can poke holes in the logic of a creator being all-knowing, just, and all-powerful; all three of which are claimed by believers. Alternatively, you can also focus on the all-knowing aspect specifically by illustrating that it is impossible for free will to exist if god is all-knowing. At least not the version of free will that most people refer to. If you want to claim that free will can exist even if there is only one possible time line then that’s another argument.