You can just post a request for testers in the Poser or jobs forum, and then see who replies.  When I have been involved in testing its usually been emailed in the zip file that would be used for a purchaser.

The other way is to post it to your website or a file share site and send the tester the link. 

Sending the zip  tests the installation and that the product is complete. If its early beta testing then just zip and send whatever file is being tested.

 

There used to be a free merchant utility that would check version numbers, file path length for mac versions. I dont know if it is still available. The version number in files should be the lowest version the product works in , it used to be 4.01 or just 4 . You could probably use 5,6 or 6 now.  If you dont do that the user will get error messages and possibly a lot of them, which is bad. Also check that the file paths  are relative paths and that no geometries are embedded.  There were some python scripts that would automate that process.