How I found a bug in Intel Skylake processors (2017)
The problem with bugs deep in the stack is that it is really time consuming to establish that they are in fact as deep as they are.<p>I wrote a Swift iOS app once, and came across an issue with one of the collection classes.<p>Of course, nobody thinks that the Swift libs will be wrong as a first guess. So I worked through a number of hypotheses about my own code, slowly stripping out pieces that I thought might contain an error. And then combinations. I also tried reducing the number of entries just to simplify the logs. This worked, but of course you are not going to think that there's a library bug affecting collections with size > 16, and it wasn't actually a theory until I randomly decided to reduce the n. I also discovered that it worked just fine on release but not debug, so I thought maybe I have some race condition.<p>More and more stripping down occurred, until I eventually gave up using my own project and just started a new one just to see about the collection class. I did it for the sake of being thorough, rather than actually thinking the lib had a bug in its debug implementation. But lo and behold, when I managed to make it reproducible and put it on SO, someone from Apple acknowledged that they could also see it, and they fixed it.<p>Naturally if I'd gone direct to testing the lib I'd have saved a huge amount of time, but I guess that's the tradeoff from the most sensible heuristic: test your own code first, the bug is there.