Generic Way to Duplicate Site and Play With Before Upgrade?

I’ve been seeing A LOT of posts of upgrade disasters (also been seeing that there’s no problems upgrading too, to be fair) and had a disaster myself on a blog, but downgraded back to 2.5.1 for now and all is well again.

Does anyone know of a way of duplicating a site, putting it in a protected portion of a server, make changes to the duplicate site to see if it breaks, test it, and if satisfied, upload it to the correct server directory and make it live?

I’m using Dreamhost, if that would help in answering the question…