Sinon stubbing of function

index.js

function getTodos(listId, callback) {
    helpers.makeHttpCall({
        url: '/todo/' + listId + '/items',
        success: function (data) {
            // Node-style CPS: callback(err, data)
            callback(null, data);
        }
    });
}
// This wrapper is required for our stubbing to work
const helpers = {
    makeHttpCall: () => jQuery.ajax(arguments)
};
module.exports = { getTodos, helpers };

test.js

const sinon = require('sinon')
const { helpers, getTodos } = require("../index")

afterAll(function () {
    // When the test either fails or passes, restore the original
    // makeHttpCalll function (Sinon.JS also provides tools to help
    // test frameworks automate clean-up like this)
    helpers.makeHttpCall.restore();
});

it('makes a GET request for todo items', function () {
    // That's the reason why we wrapped our function in an object... so that we can stub it.
    sinon.stub(helpers, 'makeHttpCall');
    //
    getTodos(42, 'whatever');

    // this will fail if you change the url that is passed into makeHttpCall function
    expect(helpers.makeHttpCall.calledWithMatch({ url: '/todo/42/items' })).toBeTruthy();
});