Hey Bob! Hope you’re well and sorry that we’ve taken until now to get you a reply. You have the right idea regarding testing on a dev/staging environment 🙂
You actually don’t need an active license at all on the dev/staging site, if you’re installing the plugins manually. The plugin works 100% without a key in place. Basically you’d download Events 3.0.3 from WordPress.org and then PRO 3.0.5 from tri.be, and you’d be able to install them/use them in full without entering a key in place.
That’d probably be the easiest route, but if you wanted to unlink the key from your production site / add it to dev for the testing process, you can totally do that from here on the site. We’ve got a tut that covers this here: https://theeventscalendar.com/finding-your-pro-license-key-re-downloading-the-plugin/#key_disconnect.
Hope that helps. Let me know if I missed anything or if you’re stuck, and I’ll do what I can to get you sorted.