Sinon does not seem to spy for an event handler callback

Question

I'm testing a backbone view with Jasmin, Simon and jasmin-simon.

Here is the code:

var MessageContainerView = Backbone.View.extend({
    id: 'messages',
    initialize: function() {
        this.collection.bind('add', this.addMessage, this);
    },
    render: function( event ) {
        this.collection.each(this.addMessage);
        return this;
    },
    addMessage: function( message ) {
        console.log('addMessage called', message);
        var view = new MessageView({model: message});
        $('#' + this.id).append(view.render().el);
    }
});

Actually, all my tests pass but one. I would like to check that addMessage is called whenever I add an item to this.collection.

describe('Message Container tests', function(){
    beforeEach(function(){
        this.messageView = new Backbone.View;
        this.messageViewStub = sinon.stub(window, 'MessageView').returns(this.messageView);

        this.message1 = new Backbone.Model({message: 'message1', type:'error'});
        this.message2 = new Backbone.Model({message: 'message2', type:'success'});
        this.messages = new Backbone.Collection([
            this.message1, this.message2            
        ]); 

        this.view = new MessageContainerView({ collection: this.messages });
        this.view.render();

        this.eventSpy = sinon.spy(this.view, 'addMessage');
        this.renderSpy = sinon.spy(this.messageView, 'render');
        setFixtures('<div id="messages"></div>');
    });
    afterEach(function(){
        this.messageViewStub.restore();
        this.eventSpy.restore();
    });

    it('check addMessage call', function(){
        var message = new Backbone.Model({message: 'newmessage', type:'success'});
        this.messages.add(message);

        // TODO: this fails not being called at all
        expect(this.view.addMessage).toHaveBeenCalledOnce();
        // TODO: this fails similarly
        expect(this.view.addMessage).toHaveBeenCalledWith(message, 'Expected to have been called with `message`');
        // these pass
        expect(this.messageView.render).toHaveBeenCalledOnce();
        expect($('#messages').children().length).toEqual(1);
    });
});

As you can see addMessage is called indeed. (It logs to the console and it calls this.messageView as it should. What do I miss in spying for addMessage calls?

thanks, Viktor

Answer 1

I'm not quit sure but, as I understand it, the following happens:

1. You create a new view which calls the initialize function and bind your view.addMessage to your collection.
2. Doing this, Backbone take the function and store it in the event store of your collection.
3. Then you spy on view.addMessage which means you overwrite it with a spy function. Doing this will have no effect on the function that is stored in the collection event store.

So their are some problems with your test. You view has a lot of dependencies that you not mock out. You create a bunch of additional Backbone Models and Collections, which means you not test only your view but also Backbones Collection and Model functionality.

You should not test that collection.bind will work, but that you have called bind on the collection with the parameters 'add', this.addMessage, this

initialize: function() {
    //you dont 
    this.collection.bind('add', this.addMessage, this);
},

So, its easy to mock the collection:

var messages = {bind:function(){}, each:function(){}}
spyOn(messages, 'bind');
spyOn(messages, 'each');
this.view = new MessageContainerView({ collection: messages });

expect(message.bind).toHaveBeenCalledWith('bind', this.view.addMessage, this.view);

this.view.render()

expect(message.each).toHaveBeenCalledWith(this.view.addMessage);

... and so on

Doing it this way you test only your code and have not dependencies to Backbone.