Since you are using Gmail and assuming your email is
firstname.lastname@example.org, you can use
email@example.com for the test account. Gmail ignores everything after the plus sign, and will redirect all emails send there to your regular account. After you register you will be asked if you want to associate the two accounts, the registration process is smart enough to link
firstname.lastname@example.org, but you can simply say no.
It would be nice if you add a link to your test account in your main's account about box, and vice versa, so we know that it's a legit test account. Do not use the test account to vote on your main account's posts, this would be vote fraud, you'll be caught and punished severely (I've heard rumours there's spanking involved).