You can use a cap checker but values may be too low for some testers. Short test lead length is also important when measuring small value caps. Try measuring leakage of mica caps with the highest scale on your ohm meter. There should be no readable leakage.
Now for your first point, they seldom go bad. When mica caps do cause a problem it's usually a crackeling noise.
Norm
:hello im working on a zenith 10s464, i replaced all caps except the micas, allthough supposedly they never go bad,how can i test these caps . i have a heathkit capacitester can i use this? thank you for any info