Jasmine and AngularJS - how to test a factory function when the function is used as a dependency

I have the following simple factory that i would like write a unit test around.

(function () {
"use strict";

angular
   .module("math")
    .factory("addservice", [addTwoNumbers]);

function addTwoNumbers(a, b) {
    return a + b;
}
return { add: addTwoNumbers };

})();

This is what i have so far in my test spec.

describe('adding two numbers', function () {
var addService;

beforeEach(function () {
    module('math');
    inject(function ($injector) {
        addService = $injector.get('addservice');
    });
});
it('should add two numbers', function () {
    var result = addService.addTwoNumbers(1, 1);
    expect(result).toBe(2);
});

});

When trying to run this unit test i get TypeError: addService.addTwoNumbers is not a function. I am missing something obvious so any help is greatly appreciated.