>Code that isn't tested, isn't done. Tests not only verify the expectations, but also prevent future regression

A few weeks ago someone at the company implemented a feature without tests. It worked perfectly, everyone was happy. A release of another new feature by a different team a few days later broke the previous feature :)

In most situations, we don't get paid to make code "done'. We get paid to get it close enough to work most of the time.

True but cURL is in a very different situation compared to your average run-of-the-mill program. It's one of the most massively deployed open-source software out there. When you are not beholden to capricious shareholders and incompetent managers you can actually focus on quality.