I'm trying to find a way to join the bfa beta but there is no info about it, I want to be more prepared this expansion for gold farming, gearing up and leveling quick, also choosing my class, Is there any chance to join it at all? finally I want to test if it's actually worth purchasing bfa.
You can't just join beta. You can sign up for a chance to get beta but it just a matter of luck. You can log in to your battle.net account and in the tab Games & codes there should beta profile. Go there select what games you want and hope you will get it. Another ways are giveaways by fansites, streamers and youtubers, for example here is a giveaway, it's also random.
The only way to have a guarenteed beta access is to work for a fansite or be a popular streamer or youtuber.
There is still a chance, there are still giveaways coming, and there seem to new waves from blizzard going out like once a week or 2.