All the above. When I remove mine, I hold it up to the light and note the percentage of opening at ambient temperature. Mine typically is open 1/3 to 1/2.
Then, I'll hook it up directly to 12 volts and measure the time it takes to close. Mine average 1.5 - 2.0 minutes. If all is ok, a quick spray of WD40 and then reinstallation..
I've never done the oven test, but I have put the AAR into the freezer; the opening increases to 1/2 -3/4--on some AAR's, more.
Picture: Looking through hole in AAR at ambient temperature--around 75 degrees