As far as I know all test sites must be .htaccess password protected or hidden for anyone else except you so that means you can have only one test forum
Test as defined by any and all other installations besides the public one? Or any version that is running on a server and is not local? That's the real question.
Because technically I have 3 running copies. One is user/pass protected for final testing and so the other admins can see the changes, the actual forum, and my local copy for me.