You can test the resistance of each sensor with a multimeter. You should get a reading of about 1050 ohms from each sensor.
Any that are a long way out (by 100 ohms or so) will be faulty.
It is possible to test the fronts by removing each wheel and disconnecting the plug behind the wheel arch liner. Then test the cable going to the sensor.
For the rear you will need to jack up the car and disconnect the sensors (connector in the middle of the rear beam) and test each one individually.
There is another option which will avoid having to crawl about under the car. They can all be tested from under the bonnet.
You will need to remove the battery and battery box to gain better access to the multi plug on the LH side of the ABS module which is tucked away under the brake servo.
It has a plastic locking mechanism which easily slides upwards and then the plug disconnects by pulling towards the front of the car. It is a bit tight to get in there but it is possible.
If you turn the plug round and look at the pins, this is the layout...
Not all of the pins are used. You may need to get some bits of wire to poke into the connectors in order to get your test probes on, but take care not to damage them.
Doing it his way means you don't have to crawl about under the car and remove the wheels. Also it will test the integrity of the connectors and wiring from the ABS module to the sensors.
Hope this helps.
Paul