Sinon

In Practice

Spies

Secretly monitor existing function

test("launch calls missile.engage() with 'meltdown' argument", function () {
    sinon.spy(missile, 'engage'); // attach spy

    launch();

    strictEqual(missile.engage.called, true);
    strictEqual(missile.engage.getCall(0).args[0], 'meltdown');
    
    missile.engage.restore(); // remove spy
});

Stubs

Take over behaviour of existing function

test("greeting is 'Hello Earthlings' when Date.now is morning", function () {
    sinon.stub(Date, 'now').returns('morning'); // attach stub
    var result = greeting();
    strictEqual(result, 'Hello Earthlings');
    
    Date.now.restore(); // remove stub
});

Stubs

Take over behaviour of existing function

test("greeting is 'Does not compute' when Date.now throws an exception", function () {
    var nowStub = sinon.stub(Date, 'now'); // attach stub
    nowStub.throws();
    var result = greeting();
    strictEqual(result, 'Does not compute');
    
    nowStub.restore(); // remove stub
});

Exercises

• Toy exercise: jsbin.com/roxog/1/edit
• Backbone router: jsbin.com/zikoc/1/edit

Verifying Events

Spies can also be used as event callbacks

test("menu.open triggers menuOpened event", function () {
    var mySpy = sinon.spy(); // create a spy
    jQuery.on('menuOpened', mySpy);

    menu.open();

    strictEqual(mySpy.called, true);
});

Exercise

• Turn.js: jsbin.com/kuxoxe/1/edit

Mocking AJAX

test("getSuggestions makes an AJAX request", function () {
    var myServer = sinon.fakeServer.create(),
        suggestionsRoute = new RegExp('/suggestions/.+');

    // step 1
    myServer.respondWith('GET', suggestionsRoute,
            [200, { 'Content-Type': 'application/json' },
             '[{ "suggestions": ["dog", "cat"], "confidence": "95%" }]']);

    getSuggestions();
    myServer.respond(); // don't forget step 2!

    strictEqual(myServer.requests.length, 1);
    strictEqual(myServer.requests[0].method, 'GET');
    myServer.restore();
});

Exercise

• Toy exercise: jsbin.com/vorizo/1/edit

Asynchronous program flow

Some actions produce results only much later

• Network requests
• Writing to filesystem or database
• Complicated mathematical calculations
• Animations

Async Tests

var addStickyNote = function (message) {
    var fadeInDuration = 1500; // milliseconds
    fadeIn(message, fadeInDuration);
};

asyncTest("addStickyNote makes message disappear", function () {
    addStickyNote('hello world');

    setTimeout(function () {
      // this function body is run after 1500ms delay
      
      // assert message has appeared
      
      start(); // resume QUnit execution
    }, 1500);
});

Exercise

• Bloodhound: jsbin.com/bomocu/2/edit

Manipulating time

Accelerates time for functions that use setTimeout

test("menu.open triggers menuOpened event after an animation", function () {
    var timeMachine = sinon.useFakeTimers(),
        mySpy = sinon.spy();

    jQuery.on('menuOpened', mySpy);

    menu.open();
    timeMachine.tick(1000); // fast-forward 1000 milliseconds

    strictEqual(mySpy.called, true);
    timeMachine.restore();
});

Example

Video.js https://github.com/videojs/video.js/blob/stable/test/unit/media.js

Sinon Essentials

• Spies
• Stubs
• Fake callbacks
• Fake server
• Fake timers

Credits

Images (in order of appearance)

• TW Hoon, "Car Tracker", CC Attribution 4.0 International. Composite created from the following 2 images;
• LibreShot.com, "Rear lights of car. Blue Škoda Octavia.", http://libreshot.com/vehicles/cars/, CC0 Public Domain;
• Stefan-Xp, "Digitaler Meldeempfänger", https://de.wikipedia.org/wiki/Funkmeldeempf%C3%A4nger#/media/File:Funkmeldeempf%C3%A4nger_Motorola_Firestorm_3.jpg, CC Attribution-ShareAlike 3.0 Unported;
• Nathan Rupert, "Futurama Brain Slug", https://www.flickr.com/photos/nathaninsandiego/4834246209/, CC Attribution-NonCommercial-NoDerivs 2.0;