filename := "a-nonexistent-file"
	if _, err := os.Stat(filename); errors.Is(err, fs.ErrNotExist) {
		fmt.Println("file does not exist")
	}
	// Output:
	// file does not exist
}

func ExampleExpand() {
	mapper := func(placeholderName string) string {
		switch placeholderName {
		case "DAY_PART":
			return "morning"
		case "NAME":
			return "Gopher"
		}

		return ""
	}