在jasmin测试中，angularjs服务似乎是实例化的，但实际上是未定义的

Question

我有一个简单的服务，我正在尝试编写单元测试：

angular
    .module('myapp.core.services')
        .service('searchService', function(api) {
            'use strict';

            this.getFilterState = function(){
                return (sessionStorage.filterState != "undefined" ? angular.fromJson( sessionStorage.filterState ) : {} )
            }

            this.setFilterState = function(filterState){
                sessionStorage.filterState = angular.toJson(filterState);
            }
        });

这是单元测试：

/**
 * Tests for searchService service
 */
describe('searchService service', function() {
    var rootScope, svc;

    beforeEach(module('myapp.core.services'));

    beforeEach( inject(function($window, $rootScope, searchService) {
            rootScope = $rootScope;
            svc = searchService;
    }));

    it('should contain a searchService', function(){
        expect(svc).toBeDefined();
    });

    it('should return an empty object when called the first time',function(){
        console.log(svc);
        expect(svc.getFilterState()).toEqual({});
    });

});

当我运行测试时，expect(svc).toBeDefined();评估为true，但expect(svc.getFilterState()).toEqual({});会抛出错误。

错误日志：

Chrome 34.0.1847 (Mac OS X 10.8.4) LOG: {getFilterState: function (){ ... }, setFilterState: function (filterState){ ... }}
Chrome 34.0.1847 (Mac OS X 10.8.4) searchService service should return an empty object when called the first time FAILED
    Expected undefined to equal {  }.
    Error: Expected undefined to equal {  }.
        at null.<anonymous> (/myapp/assets/js/tests/core/services/searchService.js:20:38)
..................
PhantomJS 1.9.7 (Mac OS X) LOG: {getFilterState: function () { ... }, setFilterState: function (filterState) { ... }}
PhantomJS 1.9.7 (Mac OS X) searchService service should return an empty object when called the first time FAILED
    Expected undefined to equal {  }.

我还运行了返回undefined的console.log（svc.getFilterState（）），所以我有点失落。

以下是我所依据的测试（有效）：

/**
 * Tests for userPromise service
 */
describe('userPromise service', function() {
    var httpBackend, rootScope, svc;

    beforeEach(function(){
        module('myapp.core.services');
        inject(function($window, $rootScope, $httpBackend, userPromise) {
            httpBackend = $httpBackend;
            rootScope = $rootScope;
            svc = userPromise;
        });
    });

    it('should make a request to API', function() {
        httpBackend.expectGET('/api/v1/users/current').respond({a: 'b'});
        svc.then(function(v){
            expect(v.a).toEqual('b');
        },function(){
            // AAAAAAAAAAAA
            expect(false).toBe(true);
        });
        httpBackend.flush();
    });

    it('should return cached userPromise', function() {
        httpBackend.expectGET('/api/v1/users/current').respond({a: 'b'});
        httpBackend.flush();
        svc.then(function(v){
            expect(v.a).toEqual('b');
        },function(){
            // AAAAAAAAAAAA
            expect(false).toBe(true);
        });
    });

    it('should reject in case of failure', function() {
        httpBackend.expectGET('/api/v1/users/current').respond(500);
        svc.then(function(){
            // AAAAAAAAAAAA
            expect(false).toBe(true);
        },function(){
            expect(true).toBe(true);
        });
        httpBackend.flush();
    });
});