This is a technical forum, and licensing is a legal matter. You cannot get any authoritative answers about licensing here.
Here follows my layman answer: If you have a server that is running a production workload, that server needs to be licensed. But if you are only buying the machine and do not install SQL Server on it, you can add the license later. The license is not tied to the machine - it's basically only a piece of paper.
Would it be the case, that on one server you only want to run testing, but not be in production, you could run Developer Edition in that phase. Developer Edition has all the features of Enterprise, but is not licensed for production.
For more a authoritative answer, you need to contact your local Microsoft representative.