What is the difference between a wallet account and a test account?

A wallet account follows your wallet everywhere; a test account lives in one browser.

A wallet account is tied to your wallet address, so you get the same balance and positions on any device where you sign in with that wallet. A test account is tied to this browser and lasts 7 days — after that, or if you clear your browser data or switch device, you start a new one. With a wallet, just sign in again to get your account back.