When I had brake problems on my MGF, I needed to test the ABS pump, and tried the following test:
Jack one wheel up, Ignition On, Engine Off, Bonnet Up. Rotate the jacked-up wheel and you should hear the ABS unit 'chatter'. Repeat for each wheel. You may need a 2nd person to listen for you while you rotate the wheel.
Make sure the car is secure on its jack/supports before spinning the wheel.
On the MG, the ABS unit was fine - the problems where elsewhere (just about everywhere else in fact).
If you want a nice simple test, try full brakes while driving in reverse. This is very likely to cause the ABS to control the brakes as the little rear brakes will attempt to be the main brakes while the powerful front brakes will lock. Make sure you have sufficient space for the extended stopping distance.
If you think you have real ABS problems then make sure you get the entire brake system looked at and properly tested. it's one part of the car that really has to work. Good Luck - brake problems can be worrying, and many garages are quite poor at fixing the problems.