XF 1.5 Creating a sandbox of my Xenforo server

I am wanting to create a sandbox version of my web server that I can use to test plugins and other development before installing it on the live website. The only people that would have access is myself and one other web developer.

The reason I want to ask if this is allowed is because the sandbox would essentially be a separate install of xenforo. Is that allowed? or what requirements would I need to meet without breaking terms and conditions of my xenforo purchase.