Not able to create spy on method

My service is

var testappserviceone = angular.module('testappserviceonemodule',[])

testappserviceone.factory('testappServiceone',[function(){
    return function (x,y) {

        function addobj (x,y){
            return x+y;
        }

        return{
            add:addobj
        }
    }
}]);

My test suite is

describe('testappserviceone add method functionality', function(){

    beforeEach(function () {
        spyOn(testappServiceone(10,15),'add').and.callThrough();
    });

    it('testappServiceone add method functionality', function() {
        testappServiceone(10,15).add();
        expect(testappServiceone(10,15).add).toHaveBeenCalled();
    });

});

The Exception I am getting is

Expected a spy, but got Function.

I think spy() is not creating a spy . Please help me in understanding and solving this problem.