googleData.ts

export interface GoogleData {
  id: number;
  country: string;
  zipCode: string;
}

sharedService.service.spec.ts

import { TestBed } from '@angular/core/testing';
import { HttpClientTestingModule, HttpTestingController } from '@angular/common/http/testing';
import { SharedService } from './sharedService.service';


describe('Shared service:', () => {

  beforeEach(() => {
    TestBed.configureTestingModule({
      providers: [SharedService],
      imports: [HttpClientTestingModule]
    });
    // HttpClientTestingModule - Extended interactions between a data service and the HttpClient can be complex
    // and difficult to mock with spies.
   //  The HttpClientTestingModule can make these testing scenarios more manageable.
  });
    describe(':', () => {

      function setup() {
        const sharedService = TestBed.get(SharedService);
        const httpTestingController = TestBed.get(HttpTestingController);
        return { sharedService, httpTestingController };
      }

      it('should call the google\'s map data', () => {
        const { sharedService, httpTestingController } = setup();
        const mockGoogleMapData = {id: 1, country : 'United states of america', zipcode: '56743'};
        sharedService.getGoogleMapData().subscribe(data => {
          expect(data.mapData).toEqual(mockGoogleMapData);
        });

        const req = httpTestingController.expectOne('https:www.google.com/googleMapData');

        expect(req.request.method).toBe('GET');

        req.flush({
          mapData: mockGoogleMapData
        });
      });

      afterEach(() => {
        const { httpTestingController } = setup();
        httpTestingController.verify();
      });
    });
});

sharedService.service.ts

import { Injectable } from '@angular/core';
import { HttpClient, HttpHeaders } from '@angular/common/http';
import { Observable } from 'rxjs';
import { GoogleData } from './googleData';

@Injectable({ providedIn: 'root' })
export class SharedService {

  constructor(private httpClient: HttpClient) { }

  public getGoogleMapData(): Observable<GoogleData> {
    const options = {
      headers: new HttpHeaders({
        'content-Type': 'application/json',
        'Authorization': 'my-auth-token'
      })
    };

    return this.httpClient.get<GoogleData>('https:www.google.com/googleMapData', options);
  }

}