Yes they need bar and entertainment on a test cruise, but the staff needed or a test cruise with 300 test guests is very different from the staff needed for 1000+ paying guests.They do have to put on bar and entertainment as they would for a full sailing, so that staff would need to be on board. Just standing rando crew up and saying "this is entertainment" wouldn't comply as I read it, as the procedure includes how entertainment interacts with passengers.
They could test sail with a partial crew, but bringing additional crew on then invokes additional process for red/green crew status, and if you fall to Red crew status after a test sail they will revoke your certificate.
Also, as far as I know the only color code condition is you must be Green or Orange to perform a test sailing. Once you have your certificate, believe it or not even if you fall to Red you can still sail. When the Celebrity Edge had their inaugural sailing, they had just slipped into Red status yet they were still allowed to go ahead.