Fitnesstest with Garmin coach

I created a trainnig plan with Garmin coach for cycling. For some workouts I'm using a treadmill. In this case the treadmill always sets the average power of a power zone for the workout. Next week a fitness test is scheduled. I guess it is supposed to be an FTP test, but I'm afraid it will not work because the average power of zone 4 will be applied in the dreadmill, wich is below my current FTP. Has anyone experience with this?