How are the superpowers testing their new cyber weapons? Because they must be! Now! They have to be! No country would launch a cyber war without first testing the weapons.

So how? Well, because they don't cause immediate death and destruction, I can imagine that they consider it OK to test them in the real world, and maybe that's what we're experiencing.

Despite all the secrecy, there are things we can still deduce, & as you say, cyber-weapon testing is a racing certainty. If it's an outside state doing it then they'd like to see (a) does it work?, (b) what effect does it cause?, (c) how quickly is the target state able to restore it?

Another thing about turning the internet off is that it also has an upside for the affected country - it dramatically narrows the populace's source of information & ability to discuss/criticize issues. When it goes out, somehow the TV will still work, so we'll be back to a situation where MSM has total control of what's projected to the public. (The Indian government turns the internet off regularly for this reason.)

This would present a great opportunity to institute whatever crazy 'keep-us-safe' power grab that the authorities have next on their 'to do' list. As such, there's incentive there to either allow an attack, DIY it, or extend it, as per some critiques regarding 9-11.