** You can certainly test for shorts and opens. The drain and source pins
have ( effectively ) an internal diode connected between them - so you get
the same result as with a diode. The gate should test open to the other
Testing mosfet operation is not so easy as most mosfets need 4 volts or
more to bias the Gate so the mosfet will conduct from Drain to Source.
**Clip your meter probes to the source and drain. Place a finger between
gate and drain, then source and drain. Reverse the meter leads and perform
the above procedure. This is a very basic go, no-go test. Personally, I use
my Atlas tested, from Farnell. Easy, fast and helpful.
As there is a diode from source to drain, first put some -ve bias
on the gate so connect meter with +ve on ground (source) and -ve on gate
to impress a bias on the gate and it will stay for a while if
the device and air is dry as its a nice capacitor.
Then, without touching gate, remove leads and connect across
source and drain, first one way then the other, in one direction
it will be a diode in the other it should be off.
Then put +ve bias on gate in reverse of above procedure. Then
measure again, this will show a lower than normal diode forward
drop and conduction in the other direction as well if the mosfet
is OK. On some good mosfets as little as 1.5v gate will show
only a few ohms across source/drain - if you are fast enough.
If charge bleeds quickly then gate might have some damage or
device or air is moist. On good mosfets you can hold a gate
charge for several minutes.
On slightly bad mosfets and after putting a +ve bias, reversing
the source drain with a meter will drain some charge from
the gate - I consider this slightly marginal as it doesnt seem
to happen on a new device straight out of the tube but often
appears to happen to devices that have been close to SOA for
Caution, as mosfets dont need much to blow a gate, 20-30v is all
it takes at ultra low current to pop a gate !
You can also measure between gate and source or drain, in either
direction, should be nothing if gate hasnt popped its insulator.