You probably want to start testing with a small blast-radius though and expand the radius after fixing the obvious things. Doing country or EU wide testing would likely be quite noisy, because there will be plenty of issues of various sizes and it will be disruptive while not providing as much more information as the disruption would cost. Fixing smaller things first and then expanding to larger scale testing to catch the remaining or larger scale issues seems like the better approach to me, but that depends possibly on how time critical being prepared for such events is.