One of the many issues I saw today was around converting times to and from different formats. Let's say you have a timestamp in epoch, and you want to calculat

One of the many issues I saw today was around converting times to and from different formats. Let's say you have a timestamp in epoch, and you want to calculate a year long offset. You add seconds_in_year to your epoch time,, and call your date conversion library to get some kind of iso date (dd-mm-yyyy). Yes, it's wrong because seconds_in_year is not a constant, but this stuff sneaks its way into a large codebase and nobody realizes because all the tests pass until it's leap day. This is only the beginning, there are so many possible issues related to an edge case like this, while it might be a "solved problem" that doesn't mean it's something developers are thinking about every day. And don't even get me started on daylight savings time...