I didn't go into great detail in the original blurb, but first, testing configuration changes would have been lab tested using a redundant switch. Secondly, as part of our on site testing once the new software had been loaded into one of the switches we would switch a few unused (all this was done on the midnight shift, so there were plenty of spare positions) positions over to the updated switch and "played around" with a number of tests.
With our setup, configuration changes did not involve a software update per se, they were created and loaded locally and did not require taking either side of the system down.