How to tell if a fuel injector is bad?

[Dr Shuffles]

95, manual transmission, over 200k miles.

At idle, the engine sounds rough. The idle speed stays pretty steady, but it's got an uneven, lopey sound to it, sort of like a misfire. Runs fine as soon as I give it a little gas. If it was misfiring due to a problem with the coil pack, then you'd expect it to misfire at higher revs, too (right?) - so now I'm thinking fuel injectors.

First of all, does this sound like a plausible diagnosis?

Second, is there any way to confirm it? If this was one $20 part, I'd just replace it and see what happens, but I'd like to be sure.

[bazar01]

You can take temperature readings of the exhaust manifold closest to the engine block. If one cylinder is misfiring, it will be colder than the rest.
You can use an IR gun thermometer.

Once you get the cold cylinder isolated, you can test for absence of spark, fuel or compression.