The autobahn is a good, easy testing ground for cars. Almost on par with, say, Arizona. The real difficulty is little town streets in winter with snow.
And India. Nobody has even thought of tackling third-world-country roads, and with the slow and city-specific progress that is being made, I think there will be a huge gap in self-driving capabilities between countries, akin to the huge internet divide in the 80s/90s.
Or Egypt, not too long ago, I read there was only a literal handful of traffic lights in the whole country.
You don't even need to go that far. Starting from Germany, driving becomes more and more chaotic as you approach Turkey, and only get worse from there. Same as you head towards Sicily. I wouldn't trust a self-driving car in those environments.