Over time what’s known as hair cells in your ears are slowly damaged by constant use. And not just by loud music either, from everyday wear and tear too. The hair cells closest to your ear canal are the ones responsible for detecting higher frequencies, and they’re usually the first to go. So you can get an approximate idea of how much hearing you’ve already lost by listening to various high frequencies.
Headphones are definitely recommended here since your laptop’s or tablet’s speakers probably don’t have the highest fidelity. Don’t worry, there are no failures on this test, just a heap of guilt for not turning down your music back when your parents told you too.