Flying in daylight suggests that whatever the test is can't be too secret, be it testing the aircraft, the seekers or just keeping current. 

F-117A #831 was the last one to leave Palmdale on 11-Aug-08 supposedly for the TTR.  Maybe it didn't go there at all (anyone watch it arrive at TTR?).

We were not the first to spot a F-117A flying round the ranges as there's a report on http://www.fencecheck.com/ of a sighting early morning during Red Flag