Depends on the kind of backup really

Just a folder full of duplicate files? Try to open them.

Having a drive image you can restore from? Take an extra drive and try to “restore” the contents of your backup onto it. You use the extra drive because if you just use your primary drive you may brick yourself.

There’s definitely types of backups I’m not covering here but you should do research into the type of backups you want to use and the restoration process, and basically try the restoration process intermittently.

I kinda got lucky. I wanted to install a new, bigger SSD. At the same time, I had been wanting to start doing backups, but was too lazy to set it up. Two birds, one stone. Set up backups, tested it by copying everything to the new SSD. Everything worked first try!

I used rsnapshot for backups. I made a little container that spins up, pulls my data, then shuts down. And then I made a script that does that and made cron jobs for it.