test for range with goroutine

for_range.go

func TestForRange(t *testing.T) {
	m := map[string]string{
		"a": "1",
		"b": "2",
	}

	go func() {
		time.Sleep(1*time.Second)
		m["b"] = "3"
		fmt.Println("!")
	}()

	for k, v := range m {
		time.Sleep(700 * time.Millisecond)
		fmt.Println(k, v, m[k])
		fmt.Println(m)
	}
	
	/* Output: 
		a 1 1
		map[a:1 b:2]
		!
		b 2 3
		map[a:1 b:3]
	 */
}