Do you really think they didn’t test that before they got to this point?

I’m willing to bet they had been through that intersection before hundreds of times and never seen this. It’s not like it can’t detect a stoplight and they’re just out there randomly running through them all.

Of the millions of variables that were around them something blinded it to light this time. The footage from that run has probably been reviewed at nauseam at this point and is done more for them finding the problem than they could have done sitting in a closed warehouse making guesses when the car never fails to detect a red light.