Why does gin SetCookie add new cookies but not change the old ones?

I'm trying to test the Logout handler where there is a ctx.SetCookie method:

func (a *authController) Logout(ctx *gin.Context) {
	refreshToken, err := ctx.Cookie("refresh_token")
	...
	ctx.SetCookie("access_token", "", -1, "/", "localhost", false, true)
	ctx.SetCookie("refresh_token", "", -1, "/", "localhost", false, true)
	ctx.SetCookie("logged_in", "", -1, "/", "localhost", false, true)

	ctx.JSON(http.StatusOK, gin.H{"status": "success"})

}

code inside the test function:

recorder := httptest.NewRecorder()
ctx, _ := gin.CreateTestContext(recorder)
ctx.SetCookie("logged_in", "truee", 60*60, "/", "localhost", false, false)
req, _ := http.NewRequest("GET", "/logout", nil)
http.SetCookie(recorder, &http.Cookie{Name: "refresh_token", Value: "encodedRefreshToken", MaxAge: 60 * 60, Path: "/", Domain: "localhost", Secure: false, HttpOnly: true}})
http.SetCookie(recorder, &http.Cookie{Name: "access_token", Value: "encodedAccessToken", MaxAge: 60 * 60, Path: "/", Domain: "localhost", Secure: false, HttpOnly: true})
req.Header = http.Header{"Cookie": recorder.Result().Header["Set-Cookie"]}
ctx.Request = req
test.mock()
authController.Logout(ctx)

After the call, I'm trying to check if the cookies have been deleted:

coockies := recorder.Result().Cookies()
for _, c := range coockies {
	if c.Name == "access_token" {
	    assert.Equal(t, "", c.Value)
    }
    ...
}

And I face such a problem that setCookie does not change cookies , but adds new ones . That is, after calling this method, I have two pairs of cookies with access Token, etc.

And as a result, the tests do not pass. I don't understand I'm doing something wrong and can it be solved somehow? or is that how it should be ?

Use AddCookie to set cookie for the recorder.

I think you should test the Logout handler like this:

package ${your_package}

import (
	"encoding/json"
	"net/http"
	"net/http/httptest"
	"testing"

	"github.com/gin-gonic/gin"
	"github.com/stretchr/testify/assert"
)

func Logout(ctx *gin.Context) {
	// refreshToken, err := ctx.Cookie("refresh_token")
	ctx.SetCookie("access_token", "", -1, "/", "localhost", false, true)
	ctx.SetCookie("refresh_token", "", -1, "/", "localhost", false, true)
	ctx.SetCookie("logged_in", "", -1, "/", "localhost", false, true)

	ctx.JSON(http.StatusOK, gin.H{"status": "success"})
}

func setupRouter() *gin.Engine {
	r := gin.Default()
	r.GET("/logout", Logout)
	return r
}

func TestLogout(t *testing.T) {
	w := httptest.NewRecorder()
	r := setupRouter()
	req, err := http.NewRequest("GET", "/logout", nil)
	assert.Nil(t, err)
	req.AddCookie(&http.Cookie{Name: "refresh_token", Value: "encodedRefreshToken", MaxAge: 60 * 60, Path: "/", Domain: "localhost", Secure: false, HttpOnly: true})
	req.AddCookie(&http.Cookie{Name: "access_token", Value: "encodedAccessToken", MaxAge: 60 * 60, Path: "/", Domain: "localhost", Secure: false, HttpOnly: true})
	r.ServeHTTP(w, req)

	for _, v := range w.Result().Cookies() {
		if v.Name == "access_token" {
			assert.Equal(t, "", v.Value)
		}
	}
	assert.Equal(t, http.StatusOK, w.Code)
	respBody := &gin.H{}
	err = json.Unmarshal(w.Body.Bytes(), respBody)
	assert.Nil(t, err)
	assert.Equal(t, gin.H{"status": "success"}, *respBody)
}

=== RUN   TestLogout
[GIN-debug] [WARNING] Creating an Engine instance with the Logger and Recovery middleware already attached.
[GIN-debug] [WARNING] Running in "debug" mode. Switch to "release" mode in production.
- using env:	export GIN_MODE=release
- using code:	gin.SetMode(gin.ReleaseMode)
[GIN-debug] GET    /logout                   --> app.Logout (3 handlers)
[GIN] 2022/09/19 - 10:46:00 | 200 |          81µs |                 | GET      "/logout"
--- PASS: TestLogout (0.00s)
PASS

Reference: https://gin-gonic.com/docs/testing/