1. When the driver has full control of the vehicle
2. When the 'autopilot' is engaged and the driver is ready to intervene if necessary
So if the AI passes the safety test on Type 1 data, Tesla can promote it to being tested on Type 2. And if it passes that safety test it can be promoted to full autonomous control.
The 'autopilot' mode effectively does for Tesla what Google's test drivers do, but for free and on a much larger scale. Seems to me Tesla have a very strong hand here.