how to test variables in angular services

angular.module('myApp').factory('someService', function(){
    var foo = {}; // can not get access to this variable

    function setData(data){
        foo.data = data;
    }

    function getData(data){
        return foo.data;
    }

   return {
       getData: getData,
       setData: setData
   }
})

how to test this two functions for set and get some data from local variable in service?

describe('someService', function () {
    var someService,
        foo ;

    beforeEach(module('myApp'));
    beforeEach(inject(function (_someService_) {
        someService= _someServicee_;
    }));

    it('should return bundle id', function () {
        expect(someService.setData('test')) // foo.data toBe 'test'
    });
});

how to get access to foo var in service?