spyOn with Promise

I have the following function that I would like to spy... but it contains a promise... But I am getting TypeError: 'undefined' is not an object (evaluating 'modalService.showModal({}, modalOptions).then')

Because of course I have just spyOn(modalService,'showModal')

How do I account for the promise too so ??

_modalService = {
    close: function (value) { console.log(value) },
    dismiss: function (value) { console.log(value) },
    showModal: function (value) { console.log(value) }
};

spyOn(_modalService, 'close');
spyOn(_modalService, 'dismiss');
spyOn(_modalService, 'showModal');

Controller function:

user.resetPassword = function () {
            var modalOptions = {
                closeButtonText: 'Cancel',
                actionButtonText: 'Reset',
                headerText: 'Reset Password',
                bodyText: 'Are you sure you want to reset the users password?'
            };

            modalService.showModal({}, modalOptions).then(function (result) {
                if (result === 'ok') {
                    userDataService.resetPassword(user.data).then(function (result) {
                        $scope.$emit('showSuccessReset');
                    });

                };
            });
        };

Here is my unit test:

it('should allow the users password to be reset', function () {
        var controller = createController();
        controller.resetPassword();
        $httpBackend.flush();
    })