Similar to the section on testing Backbone.js apps using the Jasmine BDD framework, we're nearly ready to take what we've learned and write a number of QUnit tests for our Todo application.
Before we start though, you may have noticed that QUnit doesn't support test spies. Test spies are functions which record arguments, exceptions, and return values for any of their calls. They're typically used to test callbacks and how functions may be used in the application being tested. In testing frameworks, spies usually are anonymous functions or wrappers around functions which already exist.
In order for us to substitute support for spies in QUnit, we will be taking advantage of a mocking framework called SinonJS by Christian Johansen. We will also be using the SinonJS-QUnit adapter which provides seamless integration with QUnit (meaning setup is minimal). Sinon.JS is completely test-framework agnostic and should be easy to use with any testing framework, so it's ideal for our needs.
The framework supports three features we'll be taking advantage of for unit testing our application:
- Anonymous spies
- Spying on existing methods
- A rich inspection interface
Using this.spy() without any arguments creates an anonymous spy. This is comparable to jasmine.createSpy(). We can observe basic usage of a SinonJS spy in the following example:
test('should call all subscribers for a message exactly once', function () {
var message = getUniqueString();
var spy = this.spy();
PubSub.subscribe( message, spy );
PubSub.publishSync( message, 'Hello World' );
ok( spy.calledOnce, 'the subscriber was called once' );
});We can also use this.spy() to spy on existing functions (like jQuery's $.ajax) in the example below. When spying on a function which already exists, the function behaves normally but we get access to data about its calls which can be very useful for testing purposes.
test( 'should inspect the jQuery.getJSON usage of jQuery.ajax', function () {
this.spy( jQuery, 'ajax' );
jQuery.getJSON( '/todos/completed' );
ok( jQuery.ajax.calledOnce );
equals( jQuery.ajax.getCall(0).args[0].url, '/todos/completed' );
equals( jQuery.ajax.getCall(0).args[0].dataType, 'json' );
});SinonJS comes with a rich spy interface which allows us to test whether a spy was called with a specific argument, if it was called a specific number of times, and test against the values of arguments. A complete list of features supported in the interface can be found on SinonJS.org, but let's take a look at some examples demonstrating some of the most commonly used ones:
Matching arguments: test a spy was called with a specific set of arguments:
test( 'Should call a subscriber with standard matching': function () {
var spy = sinon.spy();
PubSub.subscribe( 'message', spy );
PubSub.publishSync( 'message', { id: 45 } );
assertTrue( spy.calledWith( { id: 45 } ) );
});Stricter argument matching: test a spy was called at least once with specific arguments and no others:
test( 'Should call a subscriber with strict matching': function () {
var spy = sinon.spy();
PubSub.subscribe( 'message', spy );
PubSub.publishSync( 'message', 'many', 'arguments' );
PubSub.publishSync( 'message', 12, 34 );
// This passes
assertTrue( spy.calledWith('many') );
// This however, fails
assertTrue( spy.calledWithExactly( 'many' ) );
});Testing call order: testing if a spy was called before or after another spy:
test( 'Should call a subscriber and maintain call order': function () {
var a = sinon.spy();
var b = sinon.spy();
PubSub.subscribe( 'message', a );
PubSub.subscribe( 'event', b );
PubSub.publishSync( 'message', { id: 45 } );
PubSub.publishSync( 'event', [1, 2, 3] );
assertTrue( a.calledBefore(b) );
assertTrue( b.calledAfter(a) );
});Match execution counts: test a spy was called a specific number of times:
test( 'Should call a subscriber and check call counts', function () {
var message = getUniqueString();
var spy = this.spy();
PubSub.subscribe( message, spy );
PubSub.publishSync( message, 'some payload' );
// Passes if spy was called once and only once.
ok( spy.calledOnce ); // calledTwice and calledThrice are also supported
// The number of recorded calls.
equal( spy.callCount, 1 );
// Directly checking the arguments of the call
equals( spy.getCall(0).args[0], message );
});SinonJS also supports two other powerful features: stubs and mocks. Both stubs and mocks implement all of the features of the spy API, but have some added functionality.
A stub allows us to replace any existing behaviour for a specific method with something else. They can be very useful for simulating exceptions and are most often used to write test cases when certain dependencies of your code-base may not yet be written.
Let us briefly re-explore our Backbone Todo application, which contained a Todo model and a TodoList collection. For the purpose of this walkthrough, we want to isolate our TodoList collection and fake the Todo model to test how adding new models might behave.
We can pretend that the models have yet to be written just to demonstrate how stubbing might be carried out. A shell collection just containing a reference to the model to be used might look like this:
var TodoList = Backbone.Collection.extend({
model: Todo
});
// Let's assume our instance of this collection is
this.todoList;Assuming our collection is instantiating new models itself, it's necessary for us to stub the model's constructor function for the the test. This can be done by creating a simple stub as follows:
this.todoStub = sinon.stub( window, 'Todo' );The above creates a stub of the Todo method on the window object. When stubbing a persistent object, it's necessary to restore it to its original state. This can be done in a teardown() as follows:
this.todoStub.restore();After this, we need to alter what the constructor returns, which can be efficiently done using a plain Backbone.Model constructor. While this isn't a Todo model, it does still provide us an actual Backbone model.
setup: function() {
this.model = new Backbone.Model({
id: 2,
title: 'Hello world'
});
this.todoStub.returns( this.model );
});The expectation here might be that this snippet would ensure our TodoList collection always instantiates a stubbed Todo model, but because a reference to the model in the collection is already present, we need to reset the model property of our collection as follows:
this.todoList.model = Todo;The result of this is that when our TodoList collection instantiates new Todo models, it will return our plain Backbone model instance as desired. This allows us to write a test for the addition of new model literals as follows:
module( 'Should function when instantiated with model literals', {
setup:function() {
this.todoStub = sinon.stub(window, 'Todo');
this.model = new Backbone.Model({
id: 2,
title: 'Hello world'
});
this.todoStub.returns(this.model);
this.todos = new TodoList();
// Let's reset the relationship to use a stub
this.todos.model = Todo;
// add a model
this.todos.add({
id: 2,
title: 'Hello world'
});
},
teardown: function() {
this.todoStub.restore();
}
});
test('should add a model', function() {
equal( this.todos.length, 1 );
});
test('should find a model by id', function() {
equal( this.todos.get(5).get('id'), 5 );
});
});Mocks are effectively the same as stubs, however they mock a complete API and have some built-in expectations for how they should be used. The difference between a mock and a spy is that as the expectations for their use are pre-defined and the test will fail if any of these are not met.
Here's a snippet with sample usage of a mock based on PubSubJS. Here, we have a clearTodo() method as a callback and use mocks to verify its behavior.
test('should call all subscribers when exceptions', function () {
var myAPI = { clearTodo: function () {} };
var spy = this.spy();
var mock = this.mock( myAPI );
mock.expects( 'clearTodo' ).once().throws();
PubSub.subscribe( 'message', myAPI.clearTodo );
PubSub.subscribe( 'message', spy );
PubSub.publishSync( 'message', undefined );
mock.verify();
ok( spy.calledOnce );
});We can now begin writing tests for our Todo application, which are listed and separated by component (e.g., Models, Collections, etc.). It's useful to pay attention to the name of the test, the logic being tested, and most importantly the assertions being made as this will give you some insight into how what we've learned can be applied to a complete application.
To get the most out of this section, I recommend looking at the QUnit Koans included in the practicals/qunit-koans folder - this is a port of the Backbone.js Jasmine Koans over to QUnit.
In case you haven't had a chance to try out one of the Koans kits as yet, they are a set of unit tests using a specific testing framework that both demonstrate how a set of tests for an application may be written, but also leave some tests unfilled so that you can complete them as an exercise.
For our models we want to at minimum test that:
- New instances can be created with the expected default values
- Attributes can be set and retrieved correctly
- Changes to state correctly fire off custom events where needed
- Validation rules are correctly enforced
module( 'About Backbone.Model');
test('Can be created with default values for its attributes.', function() {
expect( 3 );
var todo = new Todo();
equal( todo.get('text'), '' );
equal( todo.get('done'), false );
equal( todo.get('order'), 0 );
});
test('Will set attributes on the model instance when created.', function() {
expect( 1 );
var todo = new Todo( { text: 'Get oil change for car.' } );
equal( todo.get('text'), 'Get oil change for car.' );
});
test('Will call a custom initialize function on the model instance when created.', function() {
expect( 1 );
var toot = new Todo({ text: 'Stop monkeys from throwing their own crap!' });
equal( toot.get('text'), 'Stop monkeys from throwing their own rainbows!' );
});
test('Fires a custom event when the state changes.', function() {
expect( 1 );
var spy = this.spy();
var todo = new Todo();
todo.on( 'change', spy );
// Change the model state
todo.set( { text: 'new text' } );
ok( spy.calledOnce, 'A change event callback was correctly triggered' );
});
test('Can contain custom validation rules, and will trigger an invalid event on failed validation.', function() {
expect( 3 );
var errorCallback = this.spy();
var todo = new Todo();
todo.on('invalid', errorCallback);
// Change the model state in such a way that validation will fail
todo.set( { done: 'not a boolean' } );
ok( errorCallback.called, 'A failed validation correctly triggered an error' );
notEqual( errorCallback.getCall(0), undefined );
equal( errorCallback.getCall(0).args[1], 'Todo.done must be a boolean value.' );
});For our collection we'll want to test that:
- The Collection has a Todo Model
- Uses localStorage for syncing
- That done(), remaining() and clear() work as expected
- The order for Todos is numerically correct
describe('Test Collection', function() {
beforeEach(function() {
// Define new todos
this.todoOne = new Todo;
this.todoTwo = new Todo({
title: "Buy some milk"
});
// Create a new collection of todos for testing
return this.todos = new TodoList([this.todoOne, this.todoTwo]);
});
it('Has the Todo model', function() {
return expect(this.todos.model).toBe(Todo);
});
it('Uses local storage', function() {
return expect(this.todos.localStorage).toEqual(new Store('todos-backbone'));
});
describe('done', function() {
return it('returns an array of the todos that are done', function() {
this.todoTwo.done = true;
return expect(this.todos.done()).toEqual([this.todoTwo]);
});
});
describe('remaining', function() {
return it('returns an array of the todos that are not done', function() {
this.todoTwo.done = true;
return expect(this.todos.remaining()).toEqual([this.todoOne]);
});
});
describe('clear', function() {
return it('destroys the current todo from local storage', function() {
expect(this.todos.models).toEqual([this.todoOne, this.todoTwo]);
this.todos.clear(this.todoOne);
return expect(this.todos.models).toEqual([this.todoTwo]);
});
});
return describe('Order sets the order on todos ascending numerically', function() {
it('defaults to one when there arent any items in the collection', function() {
this.emptyTodos = new TodoApp.Collections.TodoList;
return expect(this.emptyTodos.order()).toEqual(0);
});
return it('Increments the order by one each time', function() {
expect(this.todos.order(this.todoOne)).toEqual(1);
return expect(this.todos.order(this.todoTwo)).toEqual(2);
});
});
});For our views we want to ensure:
- They are being correctly tied to a DOM element when created
- They can render, after which the DOM representation of the view should be visible
- They support wiring up view methods to DOM elements
One could also take this further and test that user interactions with the view correctly result in any models that need to be changed being updated correctly.
module( 'About Backbone.View', {
setup: function() {
$('body').append('<ul id="todoList"></ul>');
this.todoView = new TodoView({ model: new Todo() });
},
teardown: function() {
this.todoView.remove();
$('#todoList').remove();
}
});
test('Should be tied to a DOM element when created, based off the property provided.', function() {
expect( 1 );
equal( this.todoView.el.tagName.toLowerCase(), 'li' );
});
test('Is backed by a model instance, which provides the data.', function() {
expect( 2 );
notEqual( this.todoView.model, undefined );
equal( this.todoView.model.get('done'), false );
});
test('Can render, after which the DOM representation of the view will be visible.', function() {
this.todoView.render();
// Append the DOM representation of the view to ul#todoList
$('ul#todoList').append(this.todoView.el);
// Check the number of li items rendered to the list
equal($('#todoList').find('li').length, 1);
});
asyncTest('Can wire up view methods to DOM elements.', function() {
expect( 2 );
var viewElt;
$('#todoList').append( this.todoView.render().el );
setTimeout(function() {
viewElt = $('#todoList li input.check').filter(':first');
equal(viewElt.length > 0, true);
// Ensure QUnit knows we can continue
start();
}, 1000, 'Expected DOM Elt to exist');
// Trigget the view to toggle the 'done' status on an item or items
$('#todoList li input.check').click();
// Check the done status for the model is true
equal( this.todoView.model.get('done'), true );
});It can also be useful to write tests for any application bootstrap you may have in place. For the following module, our setup instantiates and appends to a TodoApp view and we can test anything from local instances of views being correctly defined to application interactions correctly resulting in changes to instances of local collections.
module( 'About Backbone Applications' , {
setup: function() {
Backbone.localStorageDB = new Store('testTodos');
$('#qunit-fixture').append('<div id="app"></div>');
this.App = new TodoApp({ appendTo: $('#app') });
},
teardown: function() {
this.App.todos.reset();
$('#app').remove();
}
});
test('Should bootstrap the application by initializing the Collection.', function() {
expect( 2 );
// The todos collection should not be undefined
notEqual( this.App.todos, undefined );
// The initial length of our todos should however be zero
equal( this.App.todos.length, 0 );
});
test( 'Should bind Collection events to View creation.' , function() {
// Set the value of a brand new todo within the input box
$('#new-todo').val( 'Buy some milk' );
// Trigger the enter (return) key to be pressed inside #new-todo
// causing the new item to be added to the todos collection
$('#new-todo').trigger(new $.Event( 'keypress', { keyCode: 13 } ));
// The length of our collection should now be 1
equal( this.App.todos.length, 1 );
});That's it for this section on testing applications with QUnit and SinonJS. I encourage you to try out the QUnit Backbone.js Koans and see if you can extend some of the examples. For further reading consider looking at some of the additional resources below: