How to write dynamic http request test in my case

I am trying to write a unit test for my http request

In my controller, I have something like

     $scope.test1 = function(url) {
         productFactory.getProduct(url)
             .then(function(products){
                 $scope.result = products;
              })
    } 

In my unit factory file

    angular.module('myApp').factory('productFactory', function($http) {
        var factoryObj = {};
        factoryObj.getProduct = function(url) {
            return getProductDetail(url) 
        }

        var getProductDetail = function(url) {
           return http.get('/product/' + url)
        }
        return factoryObj
    })

in my unit test, I am not sure how to write the test because url is dynamic

describe('test here', function () {
var testCtrl, scope, httpBackend, mockFactory;

// Initialize the controller and a mock scope
beforeEach(inject(function (_$controller_, _$rootScope_, _$httpBackend_,  _productFactory_) {
    scope = _$rootScope_.$new();
    httpBackend = _$httpBackend_;
    mockFactory = _productFactory_;

    testCtrl = _$controller_('testCtrl', {
        $scope: scope
    });


// the url is dynamic so I am not sure what to write here.

   httpBackend.whenGet(url).response() // not sure what to write here

}));

I am not sure how to write a http request in my case. Can anyone help me about it? Thanks!