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How to test the a new version
Sure i do. But only if you know your way around domains, Cpanel and hosting.
You can create a SUBdomain like "test.yourdomain.tld", copy your config.php of Osclass, import your DB of your Osclass and finally upload this 3.9RC version.
Then change the user in your config.php and the db name.
Again, you MUST know a few things about all that. If not, do not try it. Just wait for 3.9 to be widely used and tested and update at that time.