When all the goroutines in a synctest bubble are durably blocked and no progress can be made, synctest.Run panics. This is essentially a more limited version of the runtime's fatal error "all goroutines are asleep - deadlock!".

Currently, when this panic occurs in a test, by default you see a stack trace for the goroutine which called synctest.Run, but not for any other goroutines. This isn't especially useful. You can set GOTRACEBACK=all to see more stacks, but you shouldn't have to.

I think that ideally in this case you'd get stack traces for all goroutines in the bubble causing the panic, but not for anything else.

I'm not sure yet what the right way to implement this is: Should the panic from synctest.Run contain the relevant stack traces? Should synctest.Run print the stacks itself before panicing? Should the testing package detect the synctest.Run panic and handle printing the relevant stacks itself?