If you've got project on your PROD box that are newer then what you currently have on your TEST box the best approach is to follow these steps.
1. Open the projects in Designer on PROD.
2. Package each project into a .package file.
3. On the TEST box in the WorkflowProjects folder move the existing folders for the projects you are bring over from PROD out of the Projects folder.
4. Copy the package files into the Project folder on TEST.
To help prevent development of projects on your PROD box you can remove Designer and only have it available on your test box or another remote box. It is possible to publish projects developed on your TEST box to your PROD box through Designer on your TEST box.
I actually just helped a customer set this up. We went one step further and setup their TEST server into a managed environment, so they could use the repository functionality. This gives them version control on their projects as well.