Would be interesting to see other peoples comments on the testing of isolators?
what i have been normally doing and especially on big installs is using isolated and non isolated sounders etc.
then instead of the 20 device rule i go ten,this makes sure that i don't go over as some devices count as more than one on a loop due to their intial switch on surge current.
At commissioning i will go to a detector in between the isolators and short out pos and neg and check both isolators have kicked in. repeat for all others on loop.
I will use the isolated mcp's and make the first and last sounder on a loop isolated version.
When all devices go isolated it will be a nightmare to test but if there is nothing specific in the regs then maybe Mr Todd can shed some light if they are expected all to be tested at commission stage?