It's not about ending cleanly, it's about behaving correctly. I would say that there's nothing "basic" about testing concurrent code--it's always been hard, no

It's not about ending cleanly, it's about behaving correctly. I would say that there's nothing "basic" about testing concurrent code--it's always been hard, no matter what language you use. Exposing your concurrency guts in the API doesn't make the intrinsic complexity go away, it just shifts it somewhere else.