There are a couple of ways you could achieve this, depending on how your test/dev site is set up.
You could use a completely separate GA account and UA code - one of the risks with this is that you forget to change the code when you eventually deploy the site (or forget to change it again after some further changes in the future).
The other option is to create an additional profile within your "live" account. In that profile, add a filter that includes just the data from your test site.
You then need to make sure you exclude your test data from your "live" profile.
Presuming your test/dev site is on another (sub) domain, then the following filter in a new profile would work:
- From "Home" click on "Admin"
- Click on "filters"
- Click on "New filter"
- Make sure "Create new filter" is selected.
- Name your filter something useful such as "Test/Dev"
- Select "Custom Filter"
- Select "Include"
- In the "Filter Field" drop down, select "Hostname"
- If your dev site is, say, beta.beantin.se, you should put "beta.beantin.se" (without the quotes) as the filter pattern.
- Make sure "No" for case-sensitive is selected.
- Save your filter!