Help testing Amana cooktop exhaust fan and switch

I have an Amana gas cooktop with built-in exhaust fan. The fan has stopped working - totally dead. I removed the fan assy and the switch from the cooktop and would like some advice on how to test these with a VOM.

The fan switch is an infinitely adjustable variable rotary switch - clicks once as you move from off to on, then the fan speeds up as you continue rotating until it stops at High. There are 3 wires: Red; Black; White.
Can you please tell me I test it?

The fan assy has 4 leads: Black; Blue; Yellow w/ green; Brown
Can you please tell me I test it?

Thanks!

Is there something written on the fan itself? (say the power it needs etc.)

Here are my findings:

Fan switch:
Switch reads as open circuit in all combinations of tests to the switch leads in all possible switch settings. I would have thought at least some combination would have given me a closed circuit. I think Blk/Wht or Red/Wht should have read closed with the switch ON.

Fan:
Blk-Blu, Blk-Brn, and Brn-Blu = 0 ohms
Should mean motor windings are good.

Yellow w/ Green - Blk, Blu, or Brn = open
Yellow w/ Green must be the Ground.

A friend gave me something else to try today: test voltage between leads while manually rotating fan. This generated small voltage when testing Blu to either Blk, Brn and, according to my friend, is an indication of healthy motor windings, a common failure mode. Interesting.

So...unless corrected by someone, my diagnosis is that the fan is good and I have a faulty Switch.

One final post in case I can help someone else out and to close out this thread.

I put the fan motor back into the unit, put everything back together using the same parts (no new parts), and...it worked! So the tests I was attempting to perform on the switch that seemed to indicate it was bad, are not valid tests. I wonder what is the proper method to test this switch?

My theory is that the switch had some corrosion or gunk on it and by agitating it, it cleaned the contacts and so now works.

Thanks for all the responses.