given that the sockets have been working for the last 2 years I think I can assume it's not the wiring being wrong (or is that not what those testers are for?)
I was wondering if the relatively large current for the oven,
compared to other appliances, (on the same circuit),
may have (finally) arc'ed a shoddy joint/connection,
leading to your current (no pun intended) powerlessness.
given that the sockets have been working for the last 2 years I think I can assume it's not the wiring being wrong (or is that not what those testers are for?)