Experience report: fast-check may have just found a bug in OSX?

[josephjunker]

This just happened to me and I thought it was cool. I thought I found a bug in NestJS while using fast-check: on rare occasions my integration tests would fail with bizarre errors: nestjs/nest#15239

I cranked up the number of repetitions and it turned out to happen regularly. When the Nest team said it wasn’t a bug in Nest I chased it through Supertest (forwardemail/supertest#861), then into nodejs itself (nodejs/node#58609) and now a libuv maintainer is saying that it’s likely an OS bug (libuv/libuv#4800).

So stick another feather in the cap of property-based testing; I’ve never found a bug this deep in the stack before and fast-check is the only reason I noticed it.

[gruhn]

Damn, that’s very cool 👍

For me, fast-check managed to reproduce a segmentation fault in NodeJS + Jest once. An error you usually only see in C/C++. That was also quite amazing. The problem was hard to narrow down though and easy to workaround, so I didn’t keep investigating.