Hi there,
Using the Test Drive account to practice your skills in QuickBooks Online is an awesome idea! This account was designed for this purpose, and I'm glad you're utilizing all your resources in order to make the most of your bookkeeping with QBO.
If you have a QBO account of your own and you've logged into it using the same computer or browser, your stored Internet files are likely prompting the site to have you login with your memorized information.
In order to stop your browser from automatically logging out of the Test Drive and into your own account, try clearing the cache and cookies by following these steps: Clear cache and cookies to fix issues when using QuickBooks Online.
If you're still experiencing the same thing, I'd recommend using the Test Drive account in an Incognito window. This is a private browsing window that runs independently from the rest of your browser. Here's more information about what that is and how to use it: Browse in private.
I hope this helps. If you're still in need of assistance, please reach out to our tech support team.
Have a great day.