05 Lacetti/reno Estate 1.6

[guinness]

hello guys,hope if anyone can help....i am wondering regarding the fuel warning light .
im try to see what mileage per gallon this car does and wanted to refuel soon the fuel light would come on,but been driving for a wile and the fuel indicator as been to the red zone for at list 20miles without the warning light coming on,so is there a way to test if the light is working ??should it take longer to show,just don't want risk to run out of fuel on the middle of the road.
on my hold ford focus there was a method to light all the warning light to see if they were working,was a combination of the ing key and the button that reset the miles on the odo.
i was hopping that the lacetti/reno had something similar.
thank you