Move Subdomain content to Main Domain?

[Brainwrap]

Hi, I'm attempting to do a Drupal installation for a new client, but they want to keep the site hosted elsewhere while I work on the new site on the new server at a subdomain. SO:

domain.com => old server
test.domain.com => new server

Then, when the new site is ready to go, they'd repoint domain.com to the new server as well.

First I tried adding test.domain.com as a new main domain via Plesk. The installation worked fine. However, I don't see any way of changing test.domain.com to domain.com

I'm assuming that the solution is to create domain.com as a main domain, then create test.domain.com as a subdomain, and install Drupal there...but if I do that, can I then later move the content up to domain.com when the site is ready to go live?

Any advice/suggestions would be appreciated, thanks!