How to test a CT Sensor (Alternating Current Clamp)?
Take a resistive load of known value (say, a small space heater that lacks a fan), and use the CT on the hot wire going to it, hooked up to a meter.  You should be able to get clamp adapters that plug into an outlet and break hot and neutral out to the two "arms" before coming back together into a socket, as depicted below in a representative North American version, at an electrical supply house or even a home-improvement/hardware store.



Once you have everything set up, you should be able to use the docs for your CT to convert your meter reading to a current reading, then match that up with the nameplate wattage on your load. (space heater, electric griddle, what have you)