Question

I’m doing some testing with the Jasmine framework and I want to spy on a pub sub publish method that I’m using. However, the publish method is firing twice and I only want to spy on it the second time. I tried to just copy the publish method to another method and then spy on the original method, like so:

pubsub.publishCopy = pubsub.publish;
spyOn(pubsub, "publish");

// this call has another call to pubsub.publish. it is this
// 2nd pub sub call that I want to spy on
pubsub.publishCopy(args); 

// this shows an error because the pubsub.publishCopy is 'pointing to 
// pubsub.publish instead of being a new function with the same functionality
expect(pubsub.publish).toHaveBeenCalledWith(differentArgs); 

However, all I’m doing is just referencing the pubsub.publish method when I call pubsub.publishCopy which throws an error in my test. How would I copy the publish method correctly to suit my needs?

Answer 1

You can try

pubsub.publishCopy = function() {
    var args = Array.prototype.slice.call(arguments, 0);
    this.publish.apply(this, args);
};

It’s basically wrapping the original method in a brand-new method, instead of simply creating an extra reference to the original function object.

No idea if it’ll work, though – haven’t worked with Jasmine