What do I need to test Amplifier Output

I receive amplifers (like Rockford Fosgate) that come with a certification sheet saying what the RMS is at 2 ohms.  What type of equipment do I need to test an amplifier's watt output?  What do they use for a load?  Do they hook up a 2 ohm speaker for a load?  We get a lot of used and refurb amps and sometimes one channel will be louder than another and I was looking for a way to accuarately test amplifier output.  Also do they use a particular signal input and signal generator for a constant input level?  Please excuse my ignorance but I'm learning as fast as I can.  I am now interested in the science more than the trial and error of human ears.

Thanks,

Bob

Warehouse full of car audio

http://www.eatel.net/~amptech/elecdisc/measpwr.htm

Thank you so much for this information.