如何在不使用控制器的情况下使用httprouter进行测试？

I'm trying to write tests for a microservice I wrote using httprouter. I've previously tried to use the answers given here: How to write test with httprouter but that doesn't seem too relevant since I don't use controllers in my microservice. Any help would be greatly appreciated.

Here's what I have so far:

package main

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

    "github.com/julienschmidt/httprouter"
)

func TestCreateURL(t *testing.T) {
  expected := `{"original_url":"https://www.google.com", "short_url":"https://morning-retreat-24523.herokuapp.com/get/3578"}`
  handler := createURL
  router := httprouter.New()
  router.GET("/new/*url", handler)

  req, err := http.NewRequest("GET", "/new/https://www.google.com", nil)
  if err != nil {
      fmt.Println(err)
  }
  rr := httptest.NewRecorder()

  router.ServeHTTP(rr, req)
  if rr.Body.String() != expected {
      t.Errorf("Handler returned unexpected body: Got %v but want %v",
        rr.Body.String(), expected)
  }

}

createURL is a function like this (but with a lot more in it obviously):

func createURL(res http.ResponseWriter, req *http.Request, ps httprouter.Params) {

}