Modify shape of data returned by Angular 2 MockBackend

So I did some testing with Karma, and using MockBackend provided from '@angular/http/testing'
The shape of data returned by MockBackend is like this :

{ data: [Object1, Object2, Object3] }

however, in my real backend (Spring), I'm not adding 'data' property, so the shape of data to be like this :

[Object1, Object2, Object3]

The error will be like this :

Error: Expected Object({ data: [ Object({ cityId: 1, city: 'Lorem' }), Object({ cityId: 2, city: 'Ipsum' }), Object({ cityId: 3, city: 'Dolor' }), Object({ cityId: 4, city: 'SitAmet' }) ] }) to equal [ Object({ cityId: 1, city: 'Lorem' }), Object({ cityId: 2, city: 'Ipsum' }), Object({ cityId: 3, city: 'Dolor' }), Object({ cityId: 4, city: 'SitAmet' }) ].

How do I modify returned data from MockBackend so that it doesn't automatically add 'data' property? Or I have to switch to other mock tool?

Here is my service :

getAllCities(): Promise<City[]> {
    return this.http.get(this.getCityURL + `/fetch`).toPromise()
        .then(response =>  {
        console.log('data', response.json());
        return response.json() as City[];
     }).catch(this.handleError);
}

Here is test unit :

import { TestBed, inject } from '@angular/core/testing';
import { BaseRequestOptions, Http, Response, ResponseOptions } from '@angular/http';
import { MockBackend } from '@angular/http/testing';
import { Observable } from 'rxjs';

import { CityService } from './city.service';
import { City } from './city';

let mockBackend: MockBackend;
let cityService: CityService;

let MockCity: City = <City>{cityId: 1, city: 'Lorem'};
let MockCity2: City = <City>{cityId: 2, city: 'Ipsum'};
let MockCity3: City = <City>{cityId: 3, city: 'Dolor'};
let MockCity4: City = <City>{cityId: 4, city: 'SitAmet'};

let MockCitiesArray: Array<City> = [ MockCity, MockCity2, MockCity3, MockCity4 ];

let setup = (httpMock) => {
  TestBed.configureTestingModule({
    providers: [
      CityService,
      MockBackend,
      BaseRequestOptions,
      {
        provide: Http,
        useFactory: (backend: MockBackend, options: BaseRequestOptions) => new httpMock(backend, options),
        deps: [ MockBackend, BaseRequestOptions ]
      }
    ]
  });
  inject([ MockBackend, Http ],
    (mb: MockBackend, http: Http) => {
      mockBackend = mb;
      cityService = new CityService(http);
    })();
};


describe('CityService', () => {

  it('should return the cities array from the promise when getAllCities succeeds', (done) => {
    setup(MockSuccessGetHeroesHttp);
    spyOn(cityService, 'handleError');

    cityService.getAllCities().then((heroes) => {
      expect(cityService.handleError).not.toHaveBeenCalled();
      expect(heroes).toEqual(MockCitiesArray);
      done();
    });
  });

});

class MockFailedGetHeroesHttp extends Http {
  constructor(backend, options) {
    super(backend, options);
  }

  get() {
    return Observable.throw('error');
  }
}

class MockSuccessGetHeroesHttp extends Http {
  constructor(backend, options) {
    super(backend, options);
  }

  get() {
    return Observable.from([ new Response(new ResponseOptions({body: {data: MockCitiesArray}})) ]);
  }
}