How to use http.ResponseWriter and http.request as argument(Unit Testing) with Golang language

I just getting started learning Golang and PostgreSQL. For now, I tried to make Unit testing for CreateTodo function.
My CreateTodo function is

func CreateTodo(w http.ResponseWriter, r *http.Request) {
	CreateTodo := &models.Todo{}
	utils.ParseBody(r, CreateTodo)
	CreateTodoList := CreateTodo.CreateTodo()
	res, _ := json.Marshal(CreateTodoList)
	w.WriteHeader(http.StatusOK)
	w.Write(res)
}

I tried to make Unit Test for this function... So far I wrote some codes like

func TestCreateTodo(t *testing.T) {
	dbData := &models.Todo{
		Title: "test-title-console-check",
		Description: "test-description-console-check",
		Condition: true,
	}

	utils.ParseBody(r, dbData) // r should be r *http.Request

	submittedTodo := dbData.CreateTodo()
	res, _ := json.Marshal(submittedTodo)
	r.WriteHeader(http.StatusOK) // r should be r *http.Request
	r.Write(res)

	fmt.Println("res: ", res)
}

This is ParseBodu function in utils folder

func ParseBody(r *http.Request, x interface{}) {
	if body, err := ioutil.ReadAll(r.Body); err == nil {
		if err := json.Unmarshal([]byte(body), x); err != nil {
			return
		}
	}
}

Here, I have a problem with passing net/http(r *http.Request). I am not sure how to pass this function like argument... I tried to receive it in TestCreateTodo(t *testing.T, r *http.Request) but not working what I expected.

Is there any way to unit test for CreateTodo function??

I really appreciate your help!

Edit 1]

I tried to make a global variable

var readData *http.Request
var writeData http.ResponseWriter

and using it in the function. The reason why I make it global variables is that I usually use it in the funcs like <w http.ResponseWriter, r *http.Request>, so I thought I can use as global vars too.

so I edit my code as

var readData *http.Request
var writeData http.ResponseWriter

func TestCreateTodo(t *testing.T) {
	// w := httptest.NewRecorder()
	dbData := &models.Todo{
		Title: "test-title-console-check",
		Description: "test-description-console-check",
		Condition: true,
	}

	utils.ParseBody(readData, dbData)

	submittedTodo := dbData.CreateTodo()
	res, _ := json.Marshal(submittedTodo)
	writeData.WriteHeader(http.StatusOK)
	writeData.Write(res)

	fmt.Println("res: ", res)
}

But I got this error

As mentioned by Volker, you need to create an http request. So you are missing this line:

req, err := http.NewRequest("GET", <your endpoint>, <your body>)

As shown by the Go http package documentation, the body must be passed as a stream of bytes. You can use bytes.Buffer for this:

var body bytes.Buffer
err := json.NewEncoder(&body).Encode(dbData)

After making your request, you need to initiate a response recorder and define the handler:

res := httptest.NewRecorder()
handler := http.HandlerFunc(<your handler>)
handler.ServeHTTP(res, req)

Then you can check if your response was as expected with the assert package.

~ Zoe ~