i would need to bring some perfume testers to china (5ml each), how many testers I could bring?

If you put in your carry-on luggage, you can take as much as 100 ml (probably 20 testers). There is no limit if you put them in your luggage. However, it should be limited to self-use and reasonable amount. Otherwise, you may be taxed or your testers will be confiscated.

Thanks for your kind and quick response. Do you have any idea what is the limitation for self use for bringing to China?

Sorry, I have no idea. The immigration officers decide according to their experience. If you carry too many, they might take you as a smuggler if you have no proof that all of them are testers.