I don't know if this issue has been addressed here yet, but here goes:

We have a requirement that all content (areas, sub-areas, sites,
document libraries and documents) need to first populated on the test
environment, and then promoted to the production environment. In
effect, the test env should mirror the production env.

Does sharepoint portal server come with any tools that I can use to
promote areas and sites? If not, are you aware of any third party
tools by which the same can be implemented?