falam,
The best thing you can use to test wireless coverage, is the device that uses wifi. Why? Because access points can only tell coverage from their perspective. Wifi coverage is best determined by devices that need wifi. If it is a Windows or Mac OSX laptop, try inssider: http://www.inssider.com/ If it is an android device, Aruba Utilities is your best option: https://play.google.com/store/apps/details?id=com.arubanetworks.arubautilities
-65 and stronger is generally a good number.
To see how well other access points see each other, you can use the command "show ap arm state <name of access point>"