It would be nice if resmoke could copy the files that matter for testing to a temp directory (lets say inside of either build or /data/db) before running the tests and deleting them after. This would let developers switch branches and carry on with other work while resmoke runs.

It probably needs to copy the full jstests tree and at least a few of the binaries. Ideally, for large files (>10M?) it would try to hardlink first and fall back to a full copy if that fails (eg different file systems).