What is the logic in "life after death"?

[Nonpareil]

So, what would be the point of creating this world only to test people here to see if they'll go to heaven or hell?

Carrot and stick.

You dismiss it out of hand in your opening post, but the truth is that for the vast majority of believers, there isn't a rationalization for it. It's simply what they grow up believing. Any justification for it is entirely post hoc and doesn't really go into why the system would be designed that way to begin with; if any thought is given to it at all, it's usually something vague about free will, their deity not being able to abide evil, ineffability, et cetera.

The real reason that the hypothetical afterlife system shook out the way it did is almost certainly to do with the people who created the mythology recognizing the value of the carrot-and-stick method of control. Obey, be rewarded. Disobey, be punished. It'll happen somewhere far away, though, so we never have to provide actual proof of this - and, for bonus points, it'll happen after you're dead and last forever, for maximum intimidation points.