Disconnect while the engine is running if there is difference then its a pretty good way of saying it requires replacement.

Most MAF sensors on modern cars are the Hot Film type. The ECU supplies 5V which heats up the hot film which is then cooled as air passes over it. The more air passing it the more it cools and the return voltage to the ECU increases. The ECU can then interpret this and use it to calculate engine load.

First check that you do have a 5V supply at one of the MAF pins with the engine running. You will then need to identify which is the MAF signal terminal, and not confuse it with the wires for the Air Intake Temperature Sensor which is also located within the MAF. Having done so rev the engine up and down and observe the return voltage which should range between 1V and 4.5V. Bear in mind also that you will not be able to simulate full engine load by revving your engine on your driveway, and so your readings in this test can only be used as a guide.