Testing Ember.js Apps: Managing Dependencies
Wow! This takes me back! Please check the date this post was authored, as it may no longer be relevant in a modern context.
Fresh via EmberFest:
Ember has an amazing testing story built upon the fundamentals of encapsulation and OO programming central to the framework. Despite this, every web application will be dependent upon and need to interact with native and network APIs that are hostile: Unreliable, slow, under-documented, and not to be trusted. The challenge in testing Ember applications lies with how to handle these external entities.
In this talk, we distinguish the domain of an application from its implementation dependencies. The dependency is contained such that it avoids leaking into application code, unit tests, and acceptance tests.
As a addendum exercise, lets consider how to wrap animation frames in a service that can be mocked.
First, consider a component that schedules the animation:
// in ember-cli, app/components/animate-in.js
App.AnimateInComponent = Ember.Component.extend({
animateIn: function(){
var element = this.$();
var position = -100;
element.css({
'margin-left': ''+position+'px'
});
function animate(){
position++;
element.css('margin-left', ''+position+'px');
if (position !== 0) {
window.requestAnimationFrame(animate);
}
}
window.requestAnimationFrame(animate);
}.on('didInsertElement', 'click')
});
Though functional, this component is leaking knowledge about a browser API (requestAnimationFrame) and is difficult to disable or isolate in tests. If in the animation a component property was modified, it might also require the addition of an explicit runloop.
Lets create a service to contain the request animation API and make it easier to mock in tests. A service in Ember.js has two parts, the service itself:
// in ember-cli, app/services/animation.js
App.AnimationService = Ember.Object.extend({
init: function(){
this.frames = [];
},
scheduleFrame: function(frame){
this.frames.push(frame);
Ember.run.scheduleOnce('afterRender', this, this.scheduleAnimationFrame);
},
scheduleAnimationFrame: function(){
window.requestAnimationFrame(Ember.run.bind(this, this._animateFrame));
},
_animateFrame: function(){
var framesLength = this.frames.length;
while (framesLength--) {
var frame = this.frames.shift();
frame();
}
if (this.frames.length) {
Ember.run.scheduleOnce('afterRender', this, this.scheduleAnimationFrame);
}
}
});
And an initializer. In this example, I’m using the globals style of Ember. In ember-cli this would look different (again, see the slides):
// in ember-cli, app/initializers/animation.js
App.register('service:animation', App.AnimationService);
App.inject('component', 'animation', 'service:animation');
And now the component itself can be refactored to use this service:
// in ember-cli, app/components/animate-in.js
App.AnimateInComponent = Ember.Component.extend({
animateIn: function(){
var element = this.$();
var animation = this.animation;
var position = -100;
element.css({
'margin-left': ''+position+'px'
});
function animate(){
position++;
element.css('margin-left', ''+position+'px');
if (position !== 0) {
animation.scheduleFrame(animate);
}
}
animation.scheduleFrame(animate);
}.on('didInsertElement', 'click')
});
A unit test for this component could now easily assert that animation begins, without needing to reference the native requestAnimationFrame itself.
// in ember-cli, tests/components/animate-in-test.js
moduleForComponent('component:animate-in');
test('schedules an animation', function(){
expect(1);
var component = this.subject({
scheduleFrame: function(){
ok(true, 'animation was scheduled!');
}
});
this.append();
});
Additionally, other components can now push frames to our service, conserving how many animation frames the browser needs to manage. This is a great example of how striving to move our technology dependency into a module apart from our domain code can improve the architecture of an application.
Try out the example codebase in this JSBin.
If you joined us in Barcelona, thank you for being part of a great Ember conference. Let me know if you have any thoughts or comments, and hope to see you again!