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.