想用单元测试方法测一个http handler

想通过单元测试的方法测一个http接口handler 但是ResponseWriter不知道要怎么整，方法1,2,3,4都不行 1.报错 *http.ResponseWriter is pointer to interface, not interface 2.报错 **http.ResponseWriter does not implement http.ResponseWriter (missing Header method) 3.报错 invalid pointer type http.ResponseWriter for composite literal 4.会在调用AHandler中panic

package main

import (
    "fmt"
    "net/http"
    "testing"
)

func AHandler(w http.ResponseWriter, req *http.Request) {
    fmt.Println("ok!")
}

//unit test
func Test_AHandler(t *testing.T) {
    url := "http://127.0.0.1:12430/test
    req, _ := http.NewRequest("GET", url, nil)
    //1.w := new(http.ResponseWriter)
    //2.w := new(*http.ResponseWriter)
    //3.w := &http.ResponseWriter{}
    //4.var w http.ResponseWriter

    AHandler(w, req)
    fmt.Println("w:",w)
}

求高手指路~