Hi,
some thoughts on in circuit testing. You have to be sure not to test your application to death.
Testing with 20 A ... I see some issues:
* in "not connected" state there will be some higher DC voltage across the open test points of your measurement device. Be sure this "open circuit voltage" is rather low. I recommend less than 0.5V.
* in connected sate the current builds up to 20A. If you now disconnect there will be the energy stored in the coil that will be released and will cause very high voltage. So I guess it can easily high enough to destroy some circuit. Mind thath on manual testing the current direction applied to the coil may be random .. thus the voltage polarity will be random, too.
* Mind that there is a capacitor that keeps some energy. So when going from OPEN to CONNECTED state this energy will be going somewhere. Be sure it can´t harm any electronic parts.
* also mind ringing (resonance) when connecting and disconnecting.
* mind that on manual testing the wires of the tester may accidentally connect to random parts of your circuit... and 20A may burn a piece of copper trace.
Klaus