Do You Have a Test Site for trying stuff out?

Years ago I realized that to learn I would have to try to do things I'd never done before. It was a little scary but how else would I be able to learn if a redirect script worked, or I could install a cgi script? etc. Keep in mind I remember BBS's and AT & XT computers (don't worry if those terms are strangers to you).

Somehow I decided I needed a test site.

At first I considered a subdirectory within my first minisales site but decided that wasn't a best choice.
With the discovery of hosting accounts where you could install multiple domains for a flat monthly fee I created a separate site where I have tested cgi programs, php sites, template and images changes, and much more.

I'm not talking about tests like running creating two domains with separate PPC campaigns to see what keyword or headline worked best.

I'm taking about a site where you 'play' to see what you can do. 'What happens if I modify this line' type stuff. I'm going to hire this programmer but can he really do the job? Can I install a php site, well let's see if this works?
I usually just have the index page be a redirect to somewhere else so accidental visitors to the domain don't know where they've landed, and do the 'testing' in directories beneath the root.

My first 'can I do it, what happens if" tests were probably cgi installations.

So how about it, have you had or do you have a test site?