Test 'done' callback function of a jQuery deferred object with sinon.js

Question

I have this piece of CoffeeScript code in one of my Backbone views:

myMethod: ->
     # some code here

     $.when(
          # ...
     ).done(
          @myCallback
     )

and I wanna test that myCallback is called in the done block.

I'm not sure how to do this in Mocha.js + Sinon.js. I was able to spy on jquery and check that the when method is called:

spy = sinon.spy($, 'when')
@view.myMethod()
spy.called.should.be.true
spy.restore()

But I can't do the same with the done block because, if I have unterstood it right, it's related to the deferred object returned by the when method.

I also tried something like this:

# NOT WORKING CODE
stub = sinon.stub($.Deferred(), 'done').returns
     myCallback: sinon.stub()
@view.myMethod()
stub.called.should.be.true
stub.restore()

but still getting:

expected false to be true

Any ideas? :)

shouldn't you be using `@myCallback` instead of `@myCallback()`? Just a blind guess. But $.done doesn't exists. `done` is part of the promise object, so I guess it would be `$.Deferred().done` — pocesar, Jan 23 '13 at 17:30
@pocesar you're right, it's a typo (once I haven't used copy and paste.. sorry!). I agree with you about the deferred, I wrote it like that to make clear what I would like to achieve. I tried to spy on that and I also tried to stub the promise object, without success. Further ideas? — lucke84, Jan 23 '13 at 17:37

score 1 · Answer 1 · answered Jul 06 '16 at 08:51

You can stub $.when similarly as you would do an ajax request. Firstly you have to stub $.when and return a $.Deferred object.

var stub = sinon.stub($, "when", function (event) {
    var result = $.Deferred();
    result.args = event;
    return result;
})

After calling the function you want to test, get the return value of the specific $.when call which will be the deferred object. Resolve it manually and you can do the assertion of the @myCallback being called.

@view.myMethod()

// Get first when call
var call = $.when.getCall(0).returnValue;

// To return successful when call (having used .done() )
call.resolve();

score 0 · Answer 2 · answered Jan 23 '13 at 17:47

0

Mock it in the view class?

#arrange
view = new View
view.myCallback = sinon.spy()

#act
view.myMethod()

#assert
view.myCallback.called.should.be.true

Whether the callback was called as a deferred done handler or any other way is an implementation detail. All that should matter that the method was called (with correct arguments, if you choose).

answered Jan 23 '13 at 17:47

jevakallio

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it still seems that the function hasn't been called. Maybe the done callback could not be triggered for some reasons? – lucke84 Jan 23 '13 at 17:56
Maybe your test found a bug :) Btw. I'm not sure my sinon assert is correct, just copied from your question. Only ever used sinon with Jasmine asserts. – jevakallio Jan 23 '13 at 17:59
If so, I hope to find it out :) The function is working, it has been written without tests before I could notice it and I don't want to leave it uncovered. The assert is fine, used many times before, in fact I get a "good error". – lucke84 Jan 23 '13 at 18:02
Is the deferred an async operation? Do you need to declare tests as async with Mocha? – jevakallio Jan 23 '13 at 18:13
Or maybe if the deferred is async, the callback is not YET called at the time of assert. Don't know how to handle that with Mocha, though. – jevakallio Jan 23 '13 at 18:14
Maybe you're right and it's not yet called when I assert my expectation. How would you deal with that (even with jasmine)? – lucke84 Jan 24 '13 at 09:59
In Jasmine you would use `waitsFor`. See https://github.com/pivotal/jasmine/wiki/Asynchronous-specs – jevakallio Jan 24 '13 at 11:42

Test 'done' callback function of a jQuery deferred object with sinon.js

2 Answers2