I'll start with two broad comments. One is that pretesting of certain changes, where practical, is always done. In certain cases it's impractical, and what you saw here was an outage that made its way throughout the entire network. It's difficult to have a test environment that replicates the entirety of a very complex network across the nation. That's why in this case we would have been unable to test this in what we would call a lab environment.
On July 25th, 2022. See this statement in context.