Hello
The single test of the test button is sufficient to recreate the leak and check the differential operation. Any creation of real leakage will not only act other differentials but will not cease to be an act with a certain level of risk, in my opinion unnecessary
If the test button works instantaneously, (this is very important since it is not enough to act but also must do so in a time of the order of milliseconds), it is sufficient test to confirm the operation.
If the test button does not work, you can proceed to tests such as those mentioned by Nastor, in order to confirm that the differential works or not, since many times the defect occurs in the test circuit and the differential works perfectly, and others many times it is differential defect
The resistance value 6k8 x 7W or it can be any 7W lamp
It is good to clarify that when it is necessary to certify a differential there are testers that not only measure the actual firing intensity but also the time
For when it is required to check the facilities there are
Test sheets
These tabs not only check the operation of the differential generating a real well-calibrated leak but also checks the correct polarization of the socket. You can buy them or also assemble yourself with the attached circuit
Provided that in a circuit there is more than one differential and both are of the same type (instantaneous 0.03A), in the event of a fault that generates a trigger situation, both differentials can act at the same time. So that this does not happen, the principal must be selective but in your case this will not be possible, so to prevent them from acting both you must take tension for the test before the house differential
Regards