If you've spent enough time building software you learn that the real world almost inevitably introduces edge cases that even the most careful testing couldn't foresee. Self driving to date has proven itself not to be an exception to this.
I just can't imagine how Mercedes could be confident in a highly complex (self driving) system, designed to manage an insanely complex and unpredictable (driving) environment with no real-world tests. Maybe that's coming from the marketing/PR department and not engineering.
Having spent a lifetime building networks and software that actually makes me nervous