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Получение ошибки при модульном тестировании websocket

 Error: <spyOn> : webSocket is not declared writable or has no setter
Usage: spyOn(<object>, <methodName>)

 

вот мой сервис и компонент

 // tikcet.service.ts

    import { webSocket } from 'rxjs/webSocket';
    
    export class ticketService {
    
      ticketVar: number = 0;
    
      private ticketCtrl = new BehaviorSubject(this.ticketVar);
    
      setTicketSubject(value: number) {
        this.ticketCtrl.next(value)
      }

      getTicketSubject() {
        return this.ticketCtrl.asObservable();
      }

      getRealtimeTicket() {
        return webSocket('ws://localhost:8081');
      }
 

и в моем ticket-component.ts

 // ticket-component.ts

  constructor(private ticketService: TicketService) {

                this.ticketSubscription = this.ticketService.getRealtimeTicket().subscribe(
                  data => {
                    this.ticketService.setTicketSubject(data);
                  }
                )
            
              }



  ngOnInit(): void {

    this.realtimeTicketSubscription = this.ticketService.getTicketSubject().subscribe(
      ticket => {
        this.ticketLoader = ticket;
      }
    )
  }
 

 // ticket.service.spec.ts

import { HttpClientTestingModule } from '@angular/common/http/testing';
import { TestBed } from '@angular/core/testing';
import { BehaviorSubject } from 'rxjs';
import * as rxJsWebSocket from 'rxjs/webSocket';

import { TicketService } from './ticket.service';

describe('TicketService', () => {
  let ticketService: TicketService,
      httpClientTestingModule: HttpClientTestingModule;

  beforeEach(() => {
    TestBed.configureTestingModule({
      imports: [
        HttpClientTestingModule
      ],
      providers: [
        TicketService
      ]
    });

    ticketService = TestBed.inject(TicketService);
    httpClientTestingModule = TestBed.inject(HttpClientTestingModule);

  });


  it('should return correct beh subject', () => {

    const testTicket: number = 433;    
    ticketService.setTicketSubject(testTicket);

    ticketService.getTicketSubject()
      .subscribe(response => {
        expect(response).toBe(433);
      });

  });


  it('should return latest realtime ticket', () => {

    const testTicket: number = 433;
    let subject = new BehaviorSubject(testTicket);

    const webSocketSpy = spyOn(rxJsWebSocket, 'webSocket').and.returnValue(<any>subject);

    expect(ticketService.getRealtimeTicket()).toBe(<any>subject);
    expect(webSocketSpy).toHaveBeenCalledWith('ws://localhost:8081');

  });
})