Testing gin based REST API not getting params while using net/http/httptest

I am developing a REST API based on Gin Go, the endpoint looks something like below:

func carsByType(c *gin.Context) {
	fmt.Println("Go Request in Handler...")
	carType := c.Params.ByName("type")
	fmt.Println(carType)
	if carType != "" {

	}
	c.JSON(http.StatusBadRequest, gin.H{"result": "Bad request"})
	return
}

func main() {
	router := gin.Default()
	router.GET("/cars/:type", carsByType)
	router.Run(":80")
}

When I am making request to the endpoint via browser and cURL its just working fine, getting the carType value but when I am running the tests its returning bad request and getting carType is "".

For testing the endpoint my test code looks like this:

func TestGetcarsByType(t *testing.T) {
	gin.SetMode(gin.TestMode)
	handler := carsByType
	router := gin.Default()
	router.GET("/cars/1", handler)

	req, err := http.NewRequest("GET", "/cars/1", nil)
	if err != nil {
		fmt.Println(err)
	}
	resp := httptest.NewRecorder()
	router.ServeHTTP(resp, req)
	assert.Equal(t, resp.Code, 200)
}    	

What am I doing wrong?

router.GET("/cars/1", handler) should be router.GET("/cars/:type", handler) in your test.

Note that a better (more testable; less duplication of routes) would be to create a SetupRouter() *gin.Engine function that returns all of your routes. e.g.

// package main

// server.go
// This is where you create a gin.Default() and add routes to it
func SetupRouter() *gin.Engine {
    router := gin.Default()
    router.GET("/cars/:type", carsByType)
    
    return router
}

func main() {
    router := SetupRouter() 
    router.Run()
}

// router_test.go
testRouter := SetupRouter()

req, err := http.NewRequest("GET", "/cars/1", nil)
if err != nil {
    fmt.Println(err)
}

resp := httptest.NewRecorder()
testRouter.ServeHTTP(resp, req)
assert.Equal(t, resp.Code, 200)