Unit testing with sinon.js

During the unit testing of javaScript project, I came to know about sinon.js, I have not fully explored about this, however want to share some basics on this. So

What is Sinon.js?

Sinon.js is moking framework, which makes your test automate. The framework is made by javascript and it  has lots of feature like:- spy, stub, fakeTimer, fakeXhr and fakeServer. Later in this article, I'll describe about some of them.

Why we need Sinon.js?

You definetly want to make your unit test automate as much as you can. Making test automate means it does not depend over other test. The test will be performed alone for result pass or fail. During the unit test at some point you need to external resource for your testing, like you need to validate to response of ajax request. Or you want to validate the reponse which is came from server and you may need to test callback function. For that you need mock external resoruce, Eg:- fake server which does response your data , fake xhr which does response your request.

So basically sinon.js makes test is easy, maintainable and automate. Lest have some explore about it's feature.

Spy
Spy is a function that stores the arugments, it's calls, returned value, Through the spy you may know, how your function is working in your system, like how many times it's invoked, with which arguments its invoked. Lets take a look example how its worked.

For testig I am using qUnit framework

function add(a, b){
    alert(a + b);
}

test("Fake server is working", function () {
    var callback = this.spy(add);
    callback(10, 20);
    ok(callback.calledOnce);
    ok(callback.calledWith(10, 20), 'called with arugments');

});

First test is passed because callback() is invoked only once
Second test is passed because callback is invoked with 10, 20 arugments.

Stub
Stubs are like spies with predefined behaviours, which means you can use stub when you want to force the function/method to think the way you want. It can use all the api of spies. When you don't want to invoke direct function/method for testing, at that time you can use stubs,

Here is the simple example.
test("Fake server is working", function () {
    var callback = sinon.stub();
    callback.withArgs(42).returns(52);
    alert(callback(42));
    equal(callback(42), 52);
});

Fake server
You can create the fake server to response the data of request to server from your browser, and you can validate that resopnsed data.

Here how you can create fake server.
test("data from server", function () {
   var server = this.sandbox.useFakeServer();
    server.respondWith("GET", "/mytest",
  [200, { "Content-Type": "application/json" },
      '[{ "id": "52", "name": "Rock" }]']);
var callback = this.spy();
$.ajax({
url: "/mytest",
success: callback
        });

server.respond();
equal(server.requests.length, 1, "server request length");
ok(callback.called, "spy called once"); //failed
ok(callback.calledWith([{ id: "52", name: "Rock" }]));       //failed
});

Here we are calling the ajax function, and fake server is responding expected data.
By calledWith() method, we are cheking the relative paramters are passing on succesfull callback function. Here is  LIVE DEMO

Ofcourse I will update this article when will grab more about this topic.