> I do not understand how you can have hundreds of days of work and never test if your backups work

You outsource it, then you file a P4 ticket to test those "just in case" that will be done in a future sprint (never), but all of you more or less trust the outsourcing partner actually has their shit together.

Personally I wouldn't trust any backup system without also testing and verifying the restore, but I've worked in plenty of places where their main database is automatically backed up by AWS or whatever, and no one cares to test the restore because "Why would it be broken if it's provided by AWS?!" and similar opinions drown out the more careful ones.