Mining on the testnet: how to configure bitcoin-qt? I am trying to generate some coins with 
the client ./bitcoin-qt -testnet -gen
How can I config to what address the money go ? 

p.s.: actually I got notification for mining success but no coins in the wallet.
It is possible that you found a block, but it got orphaned. Another miner may have found a block around the same time, and for whatever reason, the next miner to find a block chose to link to theirs instead of yours.

This happens a lot on testnet because of a special rule that if no block is found for 20 minutes, the difficulty drops temporarily to 1. When this happens, typically lots of people find blocks right away, and it's a toss up which one is used by the next miner. 

You could inspect debug.log if you want to know exactly what happened.