Naytev designed multiple audience testing to take as much "busy work" off your plate as possible.
To test content against multiple audiences navigate to the specific test and click on the "clone" button. From there you'll be taken directly to the "Post Editor" where you have to option to review your test variations again.
After you've proofed your content, click on the "Preview Button" and select a different audience from the settings at the top.
All audiences will be pulled directly from the audiences you create via your Facebook Ads Manager.
TIP: Create an audience recently and don't see it? Don't forget to refresh! You'll see your new audience within 5 minutes.