The game mentions a soldier’s will influencing whether they have a gift or not. Since you can only test a soldier once, does that mean promoting a soldier a couple of times before testing might produce a different outcome than testing them as soon as they arrive? So far all of my psionics were majors or colonels at the time of testing, so that seems at least plausible, though I’ve noticed a certain degree of determinism in the game, and it would be silly for soldiers to have the ability to develop a gift but not the ability to get tested again. Do others factor play into whether a soldier has the gift or not?
I just reloaded my game about 10 times trying to figure this out and I have some results. I tested the same 5 colonels, randomly mixing them together in testing, every single one of them was psi gifted, but not every time. It is not determined when the character is created, the fact that the colonel with the lowest will became gifted but only once out of the 10 times points to randomly gifting the soldiers being tested but adding their will score to the roll.
Simply put, if you want your favorite characters to all be psychics it is easy, it will just take a long time, you will have to put them through testing by themselves or with rookies added in and keep reloading until they become psychic then work on the next character. I have gotten 2 out of the 3 as gifted in about half of the 10 tests, but I was not able to garner a 3 for 3.