code: func GoroutineCountCheck(threshold int) Check {
  	return func() error {
  		count := runtime.NumGoroutine()
  		if count > threshold {
  			return fmt.Errorf("too many goroutines (%d > %d)", count, threshold)
  		}
  		return nil
  	}
  }
docs: // GoroutineCountCheck returns a Check that fails if too many goroutines are
  // running (which could indicate a resource leak).