How do testing requirements differ across SAE automation levels?

Testing evolution across levels: L1/L2 - focus on function-specific testing (AEB scenarios, ACC scenarios), component validation, Euro NCAP protocols, driver-in-loop validation; L3 - additional testing for transition of control (take-over scenarios, minimum risk condition), driver state monitoring, longer duration testing, ODD boundary handling; L4/L5 - dramatic expansion of scenario space (no driver backup), statistically demonstrating safety equivalent to human drivers (billions of miles argument), comprehensive simulation, closed-course testing of edge cases, gradual geographic/operational expansion with field monitoring. Testing methodology shifts from discrete scenarios to coverage arguments over operational domains. Challenges include generating sufficient rare event evidence and validating ML components.