An atheist proposed a challenge he believed would prove both that god exists and also which god is the true god.  Here is his idea:

Take the sacred writings of every religion.  Close the books or roll up the scrolls.  Place all of them in a bank vault overnight.  Lock the door.  Let the followers of each religion pray or practice their religion outside the vault, doing whatever their religion teaches is to be done in order to receive an answer from god.

In the morning, open the vault.  If one of the sacred writings is open or unrolled, then its religion is the true one, its god is the true god.

Sounds like a good, valid test.

But he forgot something. 

He never figured out how to go to each of the gods to get from them commitments to participate in this experiment.  Perhaps an unopened book would result from a god's unwillingness to be tested in this way. 

The atheist thought that every god wanted people to follow him.  So an experiment like this would work because many people would begin to follow the god who opened his sacred writings. 

If gods want people to follow them, isn't it likely they already have inaugurated their chosen ways to convince people to follow them?  They probably don't need this experiment at all.