Testing Goroutine That My Code Does Not Wait For

I have a function that is executed concurrently. It's task is to run a command line method, logging an error if there is one. My main thread of execution does not wait for this method to finish. It simply returns optimistically.

How do I test my function? Assuming that I give it a cmdStr, such as {"sleep", "1"}, that works but doesn't return instantly, how can I get my test to wait for this function to finish?

I want to ensure that the actual program that runs this does not have to wait for it to finish.

func runCmd(cmdStr []string, errChan chan error) {
  cmd := exec.Command(cmdStr...)
  var out bytes.Buffer
  cmd.Stdout = &out
  err := cmd.Start()
  if err != nil {
    errChan <- err
    return
  }
  // Command started successfully, so our caller can continue.
  errChan <- nil
  err = cmd.Wait()
  if err != nil {
    log.Println(err)
  }
}

Use a wait group

wg := sync.WaitGroup{}
errc := make(chan error)
wg.Add(1)
go func() {
    runCmd([]string{"sleep", 1}, errc)
    wg.Done()
}()
err <- errc
if err != nil {
    // handle error
}
wg.Wait()

Simplest method to aware all goroutings done is to add select{} as last main.main() statement. But main() will never return this way and you should kill process explicitly.
It's also more gentle runtime.Goshed() to wait for others, but it can't provide such a strong guarantee.
And the canonical way would be

wg := sync.WaitGroup
...
wg.Add(1)
go runCmd(...)
...
wg.Wait()