One example of a bad outcome is enough for you to decide that driverless cars are unacceptably dangerous? Take a look at number of collisions per mile driven and reconsider.
You could say it is "one example" if this was a human driver running over a pedestrian. If one AI car has a bug all models with same AI have it. There is 0.5M Model 3 and counting.
I just used one example as a point and it is much less important than issue of 3rd party verification. You don't know if manufacturer fixes the bug, when it is done and you never know if it regresses.
No need to preemptively audit the code, accident statistics will clearly indicate unsafe behavior and economic/insurance disincentives[0] will induce continual safety improvements. Either a car will be safe enough to operate or it won't -- remember ~40,000 people are killed by American drivers every year.
[0]The 'Fight Club' equation.