The server is the problem… to test a server, it’s like any other appliance; it needs unplugging. But that isn’t always possible; you could arrange for it to be done outside working hours, or you could do what everyone else does, and get it visually inspected.
A visual inspection on something still plugged in is very basic, but sometimes is the best that can be done. However, this should not be done every time for years and years; at some point the server will need shutting down for a proper test. Usually this should be every 5 years from installation.
If your server isn’t a big server in a rack in a special room, but is just another computer in the office, make sure it can’t be accidentally switched off. Lockable socket covers are a great idea to prevent this.
We will never switch off a server; it’s up to you to shut it down and start it back up.