Spying on a constructor using Jasmine

Question

I am using Jasmine to test if certain objects are created and methods are called on them.

I have a jQuery widget that creates flipcounter objects and calls the setValue method on them. The code for flipcounter is here: https://bitbucket.org/cnanney/apple-style-flip-counter/src/13fd00129a41/js/flipcounter.js

The flipcounters are created using:

var myFlipCounter = new flipCounter("counter", {inc: 23, pace: 500}); 

I want to test that the flipcounters are created and the setValue method is called on them. My problem is that how do I spy on these objects even before they are created? Do I spy on the constructor and return fake objects? Sample code would really help. Thanks for your help! :)

Update:

I've tried spying on the flipCounter like this:

myStub = jasmine.createSpy('myStub'); spyOn(window, 'flipCounter').andReturn(myStub);  //expectation expect(window.flipCounter).toHaveBeenCalled(); 

Then testing for the setValue call by flipCounter:

spyOn(myStub, 'setValue');  //expectation expect(myStub.setValue).toHaveBeenCalled(); 

the first test for initializing flipCounter is fine, but for testing the setValue call, all I'm getting is a 'setValue() method does not exist' error. Am I doing this the right way? Thanks!

Answer 1

flipCounter is just another function, even if it also happens to construct an object. Hence you can do:

var cSpy = spyOn(window, 'flipCounter'); 

to obtain a spy on it, and do all sorts of inspections on it or say:

var cSpy = spyOn(window, 'flipCounter').andCallThrough(); var counter = flipCounter('foo', options); expect(cSpy).wasCalled(); 

However, this seems overkill. It would be enough to do:

var myFlipCounter = new flipCounter("counter", options); expect(myFlipCounter).toBeDefined(); expect(myFlipCounter.getValue(foo)).toEqual(bar);