[NSFW] Meaning of 1 domain in the Pro version

I am considering subscribing to the Pro version. I am thinking of purchasing a one-time license for a single site, but I would like to apply it to both a test site and a production site. If I apply it to the test site, can it still be applied to the production site? The sites are on the same server, but can a one-domain license be used for both the production and test sites? Please provide a response.