for its actual capacity, test it at 4A discharge to a 10.5V cut off., (lead acid are rated at about 1/20C)
For cold cranking amps, measure the resistance to ground of your starter motor circuit to battery negative (can usually pull the starter relay and measure from there) this gives you your load, now the cranking amps are measured as the current it can draw without falling under 7.2V from a fully charged state, so roughly a battery ESR of 7.5 milli-ohm,
At a basic level if you see the battery voltage fall under 7.2V while cranking, its likely an issue, if not and you want to know the value, take note of the voltage at that starter contact to battery negative while starting, from there its easy enough to figure out how many amps it was pulling, then another start measuring just at the battery terminals and this will let you calculate the battery ESR pretty closely.