I have a colleague who multiple times committed code that doesn't work, like at all. Why? His code is only used in tests but not in the actual application. And apparently he never even bothered to click through things even once, let alone reviewing the code.

If it doesn't work, it doesn't. You can find all these excuses. But at the end of the day, there is a difference between an end user being able to get something out of your code or not.