I was in a Helicopter unit.  The “test flights” were usually officers flying around during the day on Saturday and Sunday. They would check to see if the redfish were running on the coast or go to an airport that had a good restaurant.  Might as well have fun.  They were usually back before 5.  Night flights were common but mostly over rural areas.  You get the same test results and they wouldn’t jeopardize safety for a simple test flight by flying over densely populated areas for no reason.