How to unit test a function in a component that calls method to parent component

Question

Hello stackoverflow community.

I am working on an Angular project (1.5.6), using a component structure and currently writing some unit tests. I am still learning a lot about unit tests – especially in relation with Angular – and was hoping I can ask you for help for the following issue:

I try to test a component, that receives a callback method from it's parent component. I am trying to mock the method foo (see below the code example). And unfortunately does this method call the parent controller.

So when I try to test it, it complains, that the method is undefined. Then I thought I could mock it with spyOn, but then I get the error Error: <spyOn> : foobar() method does not exist

So I think I am unable to mock that method.

Module:

angular.module("myApp")
.component("sample", {
    "templateUrl": "components/sample/sample.html",
    "controller": "SampleController",
    "controllerAs": "sampleCtrl",
    "bindings": {
        "config": "<",
        "foobar": "&"
    }
})
.controller("SampleController",
           ["$scope",
    function($scope) {
        this.isActive = true;

        this.foo = function() {
             // do stuff
             this.isActive = false;

             // also do
             this.foobar();
        };
    }
);

Unit Test

describe("Component: SampleComponent", function() {

    beforeEach(module("myApp"));

    var sampleComponent, scope, $httpBackend;

    beforeEach(inject(function($componentController, $rootScope, _$httpBackend_) {
        scope = $rootScope.$new();
        sampleComponent = $componentController("sample", {
            "$scope": scope
        }); 
        $httpBackend = _$httpBackend_;
    }));

    it("should do set isActive to false on 'foo' and call method...", function() {
        spyOn(sampleComponent, "foobar")

        expect(sampleComponent.isActive).toBe(true);
        expect(sampleComponent).toBe("");
        expect(sampleComponent.foobar).not.toHaveBeenCalled();

        sampleComponent.foo();

        expect(sampleComponent.foobar).toHaveBeenCalled();
        expect(sampleComponent.foobar.calls.count()).toBe(1);
        expect(sampleComponent.isActive).toBe(false);
    });
});

I hope I didn't add any bugs to this, but this above is approximately what I am trying to do. Any suggestions are welcome and if the approach is wrong or more information needed, please let me know!

Answer 1

After the help from @estus (see comments in question) - I learned that I can use createSpy to resolve this issue.

    it("should do set isActive to false on 'foo' and call method...", function() {
        sampleComponent.foobar = jasmine.createSpy();

        expect(sampleComponent.isActive).toBe(true);
        expect(sampleComponent).toBe("");
        expect(sampleComponent.foobar).not.toHaveBeenCalled();

        sampleComponent.foo();

        expect(sampleComponent.foobar).toHaveBeenCalled();
        expect(sampleComponent.foobar.calls.count()).toBe(1);
        expect(sampleComponent.isActive).toBe(false);
    });

Some additional sources I used were:

• http://angular-tips.com/blog/2014/03/introduction-to-unit-test-spies/
• How does the createSpy work in Angular + Jasmine?