Service

export interface ITransferRequest {
    serviceName:string;
    amount:number
}

@Injectable()
export class TransferService
{
    transferMoneyUrl = 'https://localhost:44321/api/TransferService';

    constructor(private http:HttpClient){}

    doTransfer(transferRequest: ITransferRequest): Observable<TransferResult> {
        return this.http.post<TransferResult>(this.transferMoneyUrl, transferRequest).pipe();
      }
}

Test Code

describe('AppComponent', () => {

  let transferService: TransferService,
  mockHttp: any;

  beforeEach(async () => {

    mockHttp = jasmine.createSpyObj('mockHttp',['get', 'post']);
    transferService = new TransferService(mockHttp);

    await TestBed.configureTestingModule({
      imports: [
        RouterTestingModule
      ],
      declarations: [
        AppComponent
      ],
    }).compileComponents();

  });

  it('should do transfer', done => {
    
    const transferRequest: ITransferRequest = { serviceName: "A", amount: 1000 };

    mockHttp.get.and.returnValue(of(<TransferResult>{ result : 600 }));

    transferService.doTransfer(<ITransferRequest>transferRequest)
      .subscribe((x: TransferResult) => {   
        expect(x.result).toBe(600);
        done();
      });
   
  });

ERROR

TypeError: Cannot read properties of undefined (reading 'pipe')
    at TransferService.doTransfer (http://localhost:9876/_karma_webpack_/webpack:/src/app/services/transfer.service.ts:32:86)
    at UserContext.<anonymous> (http://localhost:9876/_karma_webpack_/webpack:/src/app/app.component.spec.ts:35:21)
    at _ZoneDelegate.invoke (http://localhost:9876/_karma_webpack_/webpack:/node_modules/zone.js/fesm2015/zone.js:372:1)
    at ProxyZoneSpec.onInvoke (http://localhost:9876/_karma_webpack_/webpack:/node_modules/zone.js/fesm2015/zone-testing.js:287:1)
    at _ZoneDelegate.invoke (http://localhost:9876/_karma_webpack_/webpack:/node_modules/zone.js/fesm2015/zone.js:371:1)
    at Zone.run (http://localhost:9876/_karma_webpack_/webpack:/node_modules/zone.js/fesm2015/zone.js:134:1)
    at runInTestZone (http://localhost:9876/_karma_webpack_/webpack:/node_modules/zone.js/fesm2015/zone-testing.js:564:1)
    at UserContext.<anonymous> (http://localhost:9876/_karma_webpack_/webpack:/node_modules/zone.js/fesm2015/zone-testing.js:580:1)
    at <Jasmine>

CodePudding user response：

First off, the TestBed configuration is totally useless in your sample. Just delete it.

Your bug is because you are providing a mock return value for get but your method under test calls post. Because the default return value for spied methods is undefined it blows up on the .pipe() with that error.