to test the callback you should create a fake implementation of the subscribe:
```javascript
spyOn(view, "trackLike");
spyOn(FB.Event, "subscribe").and.callFake(function(event, callback) {
  callback('test url', 'test element');    
});
```

Also add an expectation to check for the call of trackLike inside the callback.
```javascript
it("should call trackLike inside callback", function(){
  expect(view.trackLike).toHaveBeenCalledWith('FB Like for project', 'test element');
})
```