Short answers: Bang/tap the drain motor when it is supposed to drain. If it frees up, the bearings are shot. Replace the motor.
There is also a diagnostic mode om Whirlpool-built dishwashers I think you just hit three different cycle buttons in the same sequence 3 times quickly and (start button next?) all the lights come on. The clean light flashes codes before doing a bunch of short tests. Lookup the codes. There should be schematics sheet folded up under/behind the kickplate or door.
I DON'T KNOW THE SPECS OF YOUR MODEL, BUT HERE'S WHAT I KNOW
Make sure to fact-check my advice, I'm just speaking from the perspective of trying to get my Whirlpool/KitchenAid dishwasher to rinse all the detergent away. The one thing I have not replaced is the drain motor. It does seem louder than it used to be, so maybe I should soon, but I learned a lot from thinking the issue was the drain motor. It was an arduous and frustrating battle so you might want to read this just to avoid all the misleading advice. The drain hose on mine came with a check valve and I replaced it. Finding this out was nearly impossible, and asking for one at a hardware store will give you sideways looks. The only one from Whirlpool's website is much shorter than what came with my dishwasher. Instructions say not to extend the hose with another, so I'm guessing they just want it to got to an air gap. This makes some sense, as you would not a siphon effect if you have an anti-drain-back check valve. Anyways, my problem was that the dishes had detergent reside on them, even though it would get them clean. Yours must be full of water.
SKIP TO HERE: THE PUMP IS NOT WORKING
If you want to test the drain pump, Use a multimeter. Obviously, the drain hose routes towards the drain. (After an inverted p-trap loop or air gap somewhere) disconnect the motor wire and test for resistance (ohms) and see if you get any change. Then switch the meter to volts (not sure if it's AC or DC) and connect the test leads to the wires. Start the drain cycle to see what voltage is being supplied for the motor. Not sure where to find specs, but the voltage is likely AC. You basically just want to know if adequate power is getting to the motor.