Unit tests using withCredentials flag

Question

We are building an app that is using the withCredentials flag. Referencing this question, we were able to use the withCredentials flag. Now I'm trying to unit test the service with a mockbackend. I was able to get everything working as long as I remove the withCredentials flag.

My service:

@Injectable()
export class AccountService {
  public productParams;

  constructor(
    private http: Http) {
    // This allows the cookie to be set and sent.
    // It appears that once the cookie is set with login, it works for each call (even in other services)
     let _build = (<any>http)._backend._browserXHR.build;
     (<any>http)._backend._browserXHR.build = () => {
       let _xhr = _build();
       _xhr.withCredentials = true;
       return _xhr;
     };
  }
}

My spec file:

let service;

beforeEachProviders(() => [
    AccountService,
    BaseRequestOptions,
    MockBackend,
    provide(Http, {
        deps: [MockBackend, BaseRequestOptions],
        useFactory: (backend: MockBackend, defaultOptions: BaseRequestOptions) => {
            return new Http(backend, defaultOptions);
        },

    }),
]);

beforeEach(inject([AccountService, MockBackend], (s: AccountService, backend: MockBackend) => {
    service = s;
    const baseResponse = new Response(new ResponseOptions({ body: 'got response' }));
    backend.connections.subscribe((c: MockConnection) => c.mockRespond(baseResponse));
}));

it('should return mocked response', () => {
    service.getUsers().subscribe((res: Response) => {
        expect(res.text()).toBe('got response');
    });
});

I'm guessing the problem is because the withCredentials flag isn't mocked in my mockbackend. So how do I do this? Or can I set up my http withCredentials flag in a different way?

The error:

     6) should return mocked response
         AccountService
         _instantiateProvider@C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:18071:38 <- webpack:///~/@angular/core/src/di/reflective_injector.js:626:0
    _new@C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:18060:42 <- webpack:///~/@angular/core/src/di/reflective_injector.js:615:0
    getObjByKeyId@C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:17715:55 <- webpack:///~/@angular/core/src/di/reflective_injector.js:270:0
    _getByKeyDefault@C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:18240:52 <- webpack:///~/@angular/core/src/di/reflective_injector.js:795:0
    _getByKey@C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:18212:42 <- webpack:///~/@angular/core/src/di/reflective_injector.js:767:0
    get@C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:18021:31 <- webpack:///~/@angular/core/src/di/reflective_injector.js:576:0
    C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:26166:75 <- webpack:///~/@angular/core/testing/test_injector.js:46:46
    map@[native code]
    execute@C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:26166:33 <- webpack:///~/@angular/core/testing/test_injector.js:46:0
    C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:26255:63 <- webpack:///~/@angular/core/testing/test_injector.js:135:28
    C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:26480:29 <- webpack:///~/@angular/core/testing/testing.js:98:0 _instantiate@C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:18197:98 <- webpack:///~/@angular/core/src/di/reflective_injector.js:752:0
    14 06 2016 02:36:45.593:WARN [reporter]: SourceMap position not found for trace: TypeError: undefined is not an object (evaluating 'service.getUsers') in http://localhost:9867/base/config/karma-test-shim.js?e346472b463b1f48b98add9734c44e8d5946fda0 (line 44942)
    http://localhost:9867/base/config/karma-test-shim.js?e346472b463b1f48b98add9734c44e8d5946fda0:44942:17
    http://localhost:9867/base/config/karma-test-shim.js?e346472b463b1f48b98add9734c44e8d5946fda0:26480:29
     TypeError: undefined is not an object (evaluating 'service.getUsers') in C:/sites/Scratch/prototype_ui/config/karma-test-shim.js (line 44942)
C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:44942:17 <- webpack:///spec/services/account.service.spec.ts:26:0
C:/sites/Scratch/prototype_ui/config/karma-test-shim.js:26480:29 <- webpack:///~/@angular/core/testing/testing.js:98:0