Jasmine: mocking factory

I have the following controller defined in Angular JS that uses a service from Angular Material:

angular.module('leopDirective', [])
    .controller('MenuCtrl', function ($scope, $timeout, $mdSidenav, $log)
{

    $scope.mdSidenav = $mdSidenav;

    $scope.close = function () {
        $mdSidenav('left').close().then(function () {
            $log.debug("close LEFT is done");
            $scope.closed = true;
        });
    };

});

It depends on the service $mdSidenav that I am trying to mock with my own factory object:

describe('Controller: MenuCtrl', function() {
    var $rootScope, $scope, $controller, $q, menuCtrl,
        mock__mdSidenav = function(component) {
            return {
                isMock: true,
                component: component,
                close: function () {}
            }
        };

    beforeEach(function () {
        module('leopDirective', function($provide) {
            $provide.value('$mdSidenav', mock__mdSidenav);
        });
        inject(function ($injector) {
            $rootScope = $injector.get('$rootScope');
            $controller = $injector.get('$controller');
            $q = $injector.get('$q');
            $scope = $rootScope.$new();
        });
        menuCtrl = $controller("MenuCtrl", { $scope: $scope });
    });

    it('should create the $mdSidenav object', function () {
        expect($scope.mdSidenav).toBeDefined();
    });

    describe('managing $mdSidenav', function () {
        it('should close the menu', function () {
            var data, deferred = $q.defer(), promise = deferred.promise;
            mock__mdSidenav.close = function() {
            return promise.then(function (response) {
                data = response.success;
            });
        };
        $rootScope.$digest();
        $scope.close();
    });
});

I have the code in the following plnkr.

Apparently, the only thing that it is not working is my assignment of the $promise to the close() within the second "describe" block of the test. The execution of this test returns the following error:

TypeError: Cannot read property 'then' of undefined
TypeError: Cannot read property 'then' of undefined
    at Scope.$scope.close (app.js:7:35)

What makes me think that either the factory itself or the promise function are not correctly mocked up.

1. Is this the correct way for mocking a factory?
2. Is this the correct way for creating method that returns a promise?