How to use the @openid/appauth.FetchRequestor function in @openid/appauth

beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [ AppRoutingModule, MatCardModule, MatIconModule, MatProgressSpinnerModule ],
      declarations: [ CallbackComponent, MetadataComponent, DashboardComponent, IntroComponent, AuthenticationComponent ],
      providers: [
        {provide: APP_BASE_HREF, useValue: '/'},
        AuthorizationService,
        { provide: Requestor, useValue: new FetchRequestor()},
        { provide: 'AuthorizationConfig', useValue: environment}
      ],
    })
    .compileComponents();
  }));

BrowserAnimationsModule,
    MatButtonModule,
    MatCardModule,
    MatIconModule,
    MatListModule,
    MatProgressBarModule,
    MatProgressSpinnerModule,
    MatSidenavModule,
    MatSnackBarModule,
    MatToolbarModule,
    AppRoutingModule
  ],
  providers: [
    AuthorizationService,
    IntroDisplayService,
    { provide: Requestor, useValue: new FetchRequestor()},
    { provide: 'AuthorizationConfig', useValue: environment}
  ],
  bootstrap: [ AppComponent ]
})
export class AppModule { }

beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ DashboardComponent, AuthenticationComponent, IntroComponent ],
      imports: [MatCardModule, MatIconModule],
      providers: [
        AuthorizationService,
        IntroDisplayService,
        { provide: Requestor, useValue: new FetchRequestor()},
        { provide: 'AuthorizationConfig', useValue: environment}
     ],
    })
    .compileComponents();
  }));

beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [ AuthenticationComponent ],
      imports: [ MatCardModule, MatIconModule ],
      providers: [
        AuthorizationService,
        { provide: Requestor, useValue: new FetchRequestor()},
        { provide: 'AuthorizationConfig', useValue: environment}
     ]
    })
    .compileComponents();
  }));

beforeEach(() => {
    TestBed.configureTestingModule({
      providers: [
        AuthorizationService,
        { provide: Requestor, useValue: new FetchRequestor()},
        { provide: 'AuthorizationConfig', useValue: environment}
     ]
    });
  });

beforeEach(async(() => {
    TestBed.configureTestingModule({
      imports: [ MatCardModule ],
      declarations: [ MetadataComponent ],
      providers: [
        AuthorizationService,
        { provide: Requestor, useValue: new FetchRequestor()},
        { provide: 'AuthorizationConfig', useValue: environment}
     ]
    })
    .compileComponents();
  }));