Backbone: how to test preventDefault to be called without testing directly the callback - testing

Question

Let's say we have a simple Backbone View, like this:
class MyView extends Backbone.View
events:
'click .save': 'onSave'
onSave: (event) ->
event.preventDefault()
# do something interesting
I want to test that event.preventDefault() gets called when I click on my element with the .save class.
I could test the implementation of my callback function, pretty much like this (Mocha + Sinon.js):
it 'prevents default submission', ->
myView.onSave()
myView.args[0][0].preventDefault.called.should.be.true
I don't think it's working but this is only to get the idea; writing the proper code, this works. My problem here is that this way I'm testing the implementation and not the functionality.
So, my question really is: how can I verify , supposing to trigger a click event on my .save element?
it 'prevents default submission', ->
myView.$('.save').click()
# assertion here ??
Thanks as always :)

Answer 1

Try adding a listener on the view's $el, then triggering click on .save, then verify the event hasn't bubbled up to the view's element.
var view = new MyView();
var called = false;
function callback() { called = true; }
view.render();
// Attach a listener on the view's element
view.$el.on('click', callback);
// Test
view.$('.save').trigger('click');
// Verify
expect(called).toBeFalsy();

Answer 2

So you want to test that preventDefault is called when a click event is generated, correct?
Couldn't you do something like (in JavaScript. I'll leave the CoffeeScript as an exercise ;)):
var preventDefaultSpy;
before(function() {
preventDefaultSpy = sinon.spy(Event.prototype, 'preventDefault');
});
after(function() {
preventDefaultSpy.restore();
});
it('should call "preventDefault"', function() {
myView.$('.save').click();
expect(preventDefaultSpy.callCount).to.equal(1);
});
You might want to call preventDefaultSpy.reset() just before creating the click event so the call count is not affected by other things going on.
I haven't tested it, but I believe it would work.
edit: in other words, since my answer is not that different from a part of your question: I think your first approach is ok. By spying on Event.prototype you don't call myView so it's acting more as a black box, which might alleviate some of your concerns.