How many environments would be best practice (client is using UX)?

This question came from my new client, who will be going live next week...

Currently we have 3 models in the workspace, Dev, Test, and Prod with the Test model feeding the end user App.  At some point in the next 2 weeks we will transition the pages to point to the Production model instead of the Test model.  Do you recommend that we end up with 2 apps in the workspace, one pointing to Test and one pointing to Prod so that model builders can test functionality on pages before pushing to Prod?