Is using a coolant tester like this actually work?

Is there another method? My coolant passes the test, but the color isn't bright green anymore. It's more brownish. I have a volt tester, that I bought from radioshack I used it to test the battery when the car was off and it has 12.5V which is good. How do I test the alterantor though? I'm not exactly sure where to put the probes. To test the alternator the car has to be running but with the belt in the way, it's hard to get my hands near it.