unit testing - How can I test Broadcast event in AngularJS

Question

I have a controller which emits a broadcast event on the rootscope. I would like to test that the broacast event is fired correctly.

My code in my controller looks like this:

   $scope.$watch("pageIndex", function(){
    if($scope.pageIndex == 4)
    {
      // emit social share
      $rootScope.$broadcast('myEvent');
    }
  });

I have tried to test it with the following code:

    it('Should call myEvent when pageIndex is 4',function(){
    scope.pageIndex = 4;
    scope.$apply();
    expect(rootScope.$on).toHaveBeenCalledWith('myEvent');
});

But it tells me that the code isn't called, which I have manually tested that it does. I have then tried with the following code:

it('Should call myEvent when pageIndex is 4',function(){
    var listener = jasmine.createSpy('listener');
    rootScope.$on('myEvent', listener);
    scope.pageIndex = 4;
    scope.$apply();
    expect(listener).toHaveBeenCalled();
});

But with the same negative result. Is there a way to test that an event is broadcasted?

Answer 1

Assuming you're using Jasmine, the following is working great for me.

... other unit test setup code ...

var rootScope;
beforeEach(inject(function($injector) {
    rootScope = $injector.get('$rootScope');
    spyOn(rootScope, '$broadcast');
}));

describe("my tests", function() {
    it("should broadcast something", function() {
        expect(rootScope.$broadcast).toHaveBeenCalledWith('myEvent');
    });
});

If you're broadcasting a message and attaching objects to it, you can even test that the objects match expectations

someObj = { ... something ... };
expect(rootScope.$broadcast).toHaveBeenCalledWith('someEvent', someObj);