There is no "Test Server", the only release of the Beta 12 available is the Demo that Aethestode shared long ago publicly.
In any case, if you wanna join in the Hack's Discord server just send a PM to the user Valezio as he's one of its Moderators.
In any case, if you wanna join in the Hack's Discord server just send a PM to the user Valezio as he's one of its Moderators.