Well if you haven't actually pulled the injector from the rail, it's probably not injectors. I'm not sure what you intend to find with a multimeter... The old trick with injectors is to get a screwdriver and hold the tip to the back of the injector cap while it's running. Hold your ear on the other end and listen. You should hear it tapping/actuating. They should all sound the same. If one is odd, it's going out.

If you do think it's an injector o-ring leak, just pull the rail back from the intake manifold with everything still hooked up, and key-on to prime the fuel system. You'll see any o-ring leaks as fuel pooling at the bottom of the injector.