Currently, paver test_js_dev performs a full clean, which unfortunately means that it removes all the files under testroot/staticfiles. These are the optimized static assets used by Bok Choy tests, and they take a long time to regenerate so it would be better if they weren't removed. I swap back-and-forth between Jasmine and Bok Choy testing for my feature, so I keep getting bitten by this.
IMO a command should only clean out the directories that it itself depends upon. Since Jasmine tests don't use the optimized static assets, it shouldn't clean out the directory.
Here's an example of the Paver command's output: