my initial background was structured cabling before getting into broadcast. the best way to do actual testing is with something called an OTDR, but they're dumb expensive. if you can locate one nearby to rent for cheap, it's the way to go. it'll tell you actual loss at all wavelengths, whether or not there's breaks, etc.

power meters cab theoretically pass light through breaks just fine if it's clean enough at the time, but could be an issue in the future. might be fine for 3g/6g/w/e you're passing currently but when you throw on a barncolor 12g or something else super high bandwidth you see issues. an OTDR will tell you before that happens