Many people live their lives with for the goal of eternal heaven. While heaven certainly beats the alternative in religions like Christianity and Islam, when one stops to really think about endless eternity, it does not sound so attractive no matter what the rewards. Human nature simply does not seem to be designed with eternity in mind, and the idea of life being a test has troubling questions.
From the rather vague descriptions of a joyous place in Christianity to beautiful virgins in Islam, the kind of place heaven is has varied greatly with the time and culture. One consistent theme though is that it is eternal.
Forever is a very long time and well beyond human comprehension. People cannot imagine trillions upon trillions upon trillions of years that will never end. If the human mind cannot even possibly begin to imagine it, how can it possibly deal with it?
Also, people will have to pass the time without the kinds of stimulation they usually need. Be it through work, education, sports or hobbies, without something to reach for, people feel lost. What can people do in a place where everything is taken care of for them, infinite knowledge can be had without effort and there is no risk in anything they do? Without risk, can reward be very sweet?
Hobbies, visiting long-dead relatives and the like can keep people occupied in heaven for days, weeks, years and perhaps even centuries, but even a millennium is a drop in the bucket of all eternity. Then what happens?
Then there are those who are suffering an even worse fate in hell. Some may deserve it for a while but would not even someone murdered in an event like the Holocaust say enough is enough after watching Hitler burn for a few trillion years? How can someone be happy in heaven knowing other people are suffering horrible, eternal torment?
Finally, what form to people take in heaven? Do they all return to what they looked like when they were at their prime (or what would have been in their prime)? Do those who were deformed or ugly become prefect?
There does not seem to be any way human beings could possibly enjoy eternity in heaven without their very nature taking an entirely new form when they get there. Considering how totally horrible heaven would be even after only a few trillion years or so for any typical person, that new form would have to be something really different than anyone is now. However, if they are something so totally different, then it becomes eternal life for another being and not eternal life for them!
Furthermore, by people becoming totally different beings, has not the entire test this merciful god sent them to earth for, and what many are damned for all eternity for, just become totally meaningless? For example, many of the sins and desires that would get people into hell should not be a problem in heaven. Presumably, people would not be feeling sexual lust (or at least have an outlet for it), be motivated to steal if they could always get what they wanted anyway and would not have any of the same kinds of conflicts or desires that lead people astray in life.
In short, if there is a heaven, it certainly could not be designed for beings anything like humans are now. Either it is for different beings or it is not what anyone should strive for, but this does not fit with the idea of life being a test.