In November 2015, Google beta tested what eventually went live in February known as campaign drafts and experiments for AdWords. It basically is a way to "propose and test changes to your Search Network and Search Network with Display Select campaigns."
Well, now, Google said they are launching it for display ads.
Google posted this on Google+ saying "campaign drafts and experiments available now for Display."
Campaign drafts and experiments help you test changes to your AdWords campaigns, easily measure results, and apply the changes that are working well for your business. Whether it’s understanding performance or experimenting with different bid adjustments and strategies, marketers can now use campaign drafts and experiments to test changes in Display Network campaigns. Learn more https://goo.gl/Xr1VLh
So now you can use this feature on display ads as well.
Forum discussion at Google+.