I know of folks that have done this only to find out that the sump pit fills every 30 minutes or so, day and night. Hence, the pump comes on a LOT. And when it rains, it runs MORE than it normally would.
Yes, you can try a 'test pit' to see how fast it will fill. It might give you an idea of how much water is under there. IMO, as long as the water is condensing out of the ground on the UNDERSIDE of the plastic (which is what's happening to TT), I'd leave well enough alone. Regarding the pit - Water WILL flow to the path of least resistance. This is why it fills quickly.