Does any have experience or advice on how to stop bot sign ups?
My website is live for testing but not marketed so no one should know about it and yet a few bots are signing up already.
Is there a plugin or something available to block certain domains from signing up?
This I don’t know. Just want to help you to indetify this email. You can go to your Facebook Develper App account and check under Roles if this Test user account is visible there. And Facebook will later for sure test your login periodically (if Facebook login/sign up is available on your Sign up page).