I think that these tests serve as data collection opportunities and to rough in the the various variables. By the time the race weekend rolls around, the bikes will have evolved a bit, the track will have changed a bit and temperature will be different. But they will not be starting from total ground zero.
Each top rider probably has two bikes and spares for another. New and "improved" parts probably show up every couple of races. This "improved" part is what it killing Honda. Years ago, Doohan pointed out the problem with HRC - they are so dang smart and well funded that they change too much constantly. Last year, they gave Edwards more power and less control during mid season and his finishes suffered. This year everybody is having trouble with the front end of the RC. They'll probably find it is related to an engine change like some crank "improvement" or ignition mapping.