How to unit test AngularJs directive requiring parents directive controller with Jasmine?

I have AngularJs directive accordionPanel that requires controller of parent directive accordion. I need to test accordionPanel directive to see if model changes when I call foldUnfold function. How would I write unit test to see if the model changes on foldUnfold call. Thats simplified version of my directives and test I got so far is below that:

   .directive("accordion", [

            function() {
                return {
                    templateUrl: "otherurl",
                    transclude: true,
                    replace: true,
                    scope: {

                    },
                    controller: ["$scope",function($scope) {
                        this.isOneOpenOnly = function() {
                            return $scope.oneOpenOnly;
                        }
                    }],
                    link: function(scope, elem, attrs, ctrl, linker) {
                       // some code
                    }
                }
            }
        ])
        .directive("accordionPanel", [

            function() {
                return {
                    templateUrl: "urlblah",
                    transclude: true,
                    replace: true,
                    require: "^accordion",
                    scope: {},
                    link: function(scope, elem, attrs, ctrl, linker) {
                        scope.foldUnfold = function() {
                            // some logic here then
                            scope.changeThisModel=ctrl.isOneOpenOnly();
                        }
                    }
                }
            }
        ])

Thats my test so far:

it('Should return unfolded as true', function() {
        var scope=$rootScope.$new(),
        element=$compile("<div accordion><div accordion-panel></div></div>")(scope);
        scope.$digest();
        scope.foldUnfold(); // this is fails as scope refers to accordion but I need to access accordionPanel
        expect(scope.changeThisModel).toBe(true);
    });

The problem is I cannot get access to accordionPanel scope where foldUnfold sits. I think it might be possible to access it via $$childHead and such, but even if possible it doesn't seem like the right way to do. How would I test it then?