The documentation on upgrading JIRA strongly suggest that the upgrade should be performed in a test environment. Since the license key is derived from the Server ID it would obviously mean that a new key is needed for the test server.
Generating a new key is fairly easy, but I would like to know what the official answer is for this kind of procedure. How is the upgrade supposed to be performed with regards to license? The question applies to Confluence as well.
(And thinking of it: I there no limit on the amount of servers that can run JIRA from one license?)