Now, when cancellation occurs, all the background goroutines quickly stop and the main function returns. Of course, when main returns, a program exits, so it can be hard to tell a main function that cleans up after itself from one that does not. There’s a handy trick we can use during testing: if instead of returning from main in the event of cancellation, we execute a call to panic, then the runtime will dump the stack of every goroutine in the program. If the main goroutine is the only one left, then it has cleaned up after itself. But if other goroutines remain, they may not have been
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