Four flights were diverted by a few traffic controllers to help train a newbie (new hire). Although no safety was compromised and in the whole scheme of things it wasn’t the biggest mess-up in the airline industry in a long while, but it did break quite a few rules and caused un-needed delays on four flights.
To make things even better for the pilots, they were diverted into thunderstorms, having to navigate around them causing even more delays.
Making sure the trainee was on his game, one of the controllers instructed one of the pilots to give a wrong altitude to see if the trainee caught the mistake (which the story doesn’t say if he did).
Obviously the trainee must have done ok since nothing worse happened, but next time, maybe try the simulator!