“Perfectly” is a strong word, so I wouldn’t subscribe to this.

But it’s impossible to test software on all setups without installing it to them. There’s endless variation, so all you can do is to test on a good portion of setups and then you have to release and some setups will still have problems.

The only way to guarantee that it works on every customer’s device is by declaring every customer’s device as a beta test environment, and people don’t seem to like that either.