standard practice is to set the discharge rate to the expected use rate of discharge and measure the time lapse until cell voltage equals 1.1 volts/cell for nicads.
As stated in the previous post you will most likely not see the actual pack capacity as it is stated on the label, but if you do this and keep records on your packs you will see that they are consistently in the same range and any change will serve as an indicator as to when to trash the pack.
I number my packs and do the cycling monthly when I'm in flying mode to spot packs that are deteriorating and I have never lost an aircraft to battery failure of any sort in 34 years.
Over time you will see the capacity creep down a little but when a large change comes around you will know it. Some of my flight packs have lasted nearly 10 years with some only going 4-5 from the same suppliers.

"Big Stiks are supposed to touch a wingtip when they roll, Aren't they!?"