No, you don't.
Put the dev and test sites in subdirectories dev and test and adjust the .htaccess file to make sure visitors need to enter a username and password to get to those sites. You'd just go to mydomain.com/test or mydomain.com/dev to get to the test or dev site respectively. The public production site is at the root of the domain.
There are other options, but this one is simple to implement and maintain.
Bert
On 1/09/2011 1:54, Roger wrote:
We have 5 Drupal installations and are considering a Dev, Test and Prod multisite for each. The Dev and TEst would not be seen by the outside world. Do I have to register a domain name for each multi site.
Cheers Roger