Admit it, you are just as guilty as I am when it comes to cleaning up your test server. I usually try to delete old and unused stuff on my server at least once a year. For WordPress installs that are publicly reachable, this puts your server at risk. Missing WordPress and plugin updates are probably the number one issue for getting hacked online. Since I manage a few websites on multiple servers, I decided to use a simple command on the server to list directories with old WordPress installations:
Using the find command
This works very well on shared hosting environments running cPanel, but you can simply adjust the path to suit your server setup. Combined with a cron job, it can help you keep your test or web server updated and secure.