As the under-handed C contest (http://www.underhanded-c.org/ http://www.underhanded-c.org/) demonstrates it's perfectly possible to write code that both looks i

As the under-handed C contest (http://www.underhanded-c.org/ http://www.underhanded-c.org/) demonstrates it's perfectly possible to write code that both looks innocent and apparently is innocent when run in a testing environment. You cannot produce a set of tests that show 'this code never causes anything bad to happen' so a sufficiently skilled malicious programmer could certainly write something that could cause issues that would pass stringent code review, testing and other quality control processes (especially when they have an in-depth understanding of those processes themselves). I have no idea what has happened at Tesla, it's perfectly possible they lack processes they really should have, but you cannot prove that from the information available.