[dasil003]

I agree with this demonstration of why acceptance tests are not going to prevent bugs like this, but I'm not so sure about unit tests. I've seen good unit tests reveal a lot of similarly difficult-to-spot bugs. Granted, a really good type system like Haskell gives you more guarantees than a test suite in less rigorously typed languages ever can, but I think you're too quick to dismiss unit tests out of hand. It's a tool in the quiver, and the reason TLS stacks don't tend to have them is not because they are not valuable, but probably because the developers weren't any good at unit testing.