I think less than 19 people can fly without Flight Attendants
I really hate to do this.
There are different "test" flights. Some, one can only have FAA specified personnel. Others may or may not include cabin personnel, depending. Others may be more properly termed "positioning" flights, which may or may not demand a minimum compliment of flight attendants, even though not a revenue flight, one non-rev almost guarantees a requirement of a full complement of flight attendants.
I _always_ demand a fax detailing the type of flight and who or what may be transported. Any grey area will always be in favor of the employee.
I have found lately that the US/HP abuse of the Spectre system has led to a series of successive "waivers" on MELs and maintenance. I always demand a fax with a FAA signature on such a waiver, not that it would help me just before impact, but the fact that I always fax a copy to a safe place will protect my spouses assets. (Not that I think she would benefit from such a defunct organization but she could be protected and let all you other saps pay the bill).
BTW, US/HP is the only airline in the world to abuse the Spectre system, that from Vietnam, China and a host of middle east countries. It would be really nice if US could lead for once instead of always cutting corners, since the HP acquisition.