If you're doing this in the testing stages of a planned upgrade, you need to purchase at least one license for Windows Server 2016. With that purchase you should be able to download a non-eval version of 2012, so it will work for your testing environment. And you don't have to actually activate the license until you're ready to go ahead with your upgrade. It will run (IIRC it's up to 30 days) without activation.
this is the interim step to 2016