httpMock = injector.get(HttpTestingController) cant read properties

I don't know what I'm missing but when I added APP_INITIALIZER to load the API url in my angular application, the tests stopped working because the Auth service can't find the url

test.spec.ts

describe('AppSevice', () => {
let injector: TestBed;
let service: AppService;
let appConfig: AppConfigService;
let httpMock: HttpTestingController;

beforeAll(() => {
    console.log('beforeAll');
    TestBed.resetTestEnvironment();
    TestBed.initTestEnvironment(BrowserDynamicTestingModule, platformBrowserDynamicTesting());
});

beforeEach(async () => {
    console.log('beforeEach');
    TestBed.configureTestingModule({
        imports: [ HttpClientTestingModule, RouterTestingModule ],
        providers: [ AppConfigService, AppService ]
    });
    injector = getTestBed();
    appConfig = injector.get(AppConfigService);
    service = injector.get(AppService);
    httpMock = injector.get(HttpTestingController);  <---cant read property 'serviceBaseUrl' of undefined
});

...

AppConfigService.ts <--- this is a service load url from JSON

@Injectable({
    providedIn: 'root'
})
export class AppConfigService {
    private appConfig: any;

    constructor(private injector: Injector) {}

    async loadAppConfig() {
        let http = this.injector.get(HttpClient);

        return http
            .get('./assets/app-config.json')
            .toPromise()
            .then((data) => {
                this.appConfig = data;
                // window['app-config'] = data;
            })
            .catch((er) => {
                console.error('>>>> Problem getting app-config <<<<', er);
                this.appConfig = environment;
                // window['app-config'] = environment;
            });
    }

    config() {
        return this.appConfig;
    }
}

app.module.ts <---this is a main module with a APP_INITIALIZER

const appInitializerFn = (appConfig: AppConfigService) => {
    return async () => {
        return await appConfig.loadAppConfig();
    };
};

@NgModule({
    declarations: [ ... ],
    imports: [
        ...
    ],
    schemas: [ CUSTOM_ELEMENTS_SCHEMA ],
    providers: [
        {
            provide: HTTP_INTERCEPTORS,
            useClass: AppInterceptor,
            multi: true
        },
        AppConfigService,
        {
            provide: APP_INITIALIZER,
            useFactory: appInitializerFn,
            multi: true,
            deps: [ AppConfigService, Injector ]
        }
    ],
    bootstrap: [ AppComponent ]
})
export class AppModule {}

and this is a auth service

auth.service.ts

   @Injectable({
    providedIn: 'root'
})
export class AuthService {
    /**
     * Apiurl  of auth service
     */
    private APIURL: string;
    /**
   * Http options of auth service
   */
    private httpOptions = {
        headers: new HttpHeaders({
            'Content-type': 'application/x-www-form-urlencoded; charset=utf-8'
            // Authorization: 'Basic ...'
        })
    };

    /**
     * Creates an instance of auth service.
     * @param http 
     */
    constructor(private http: HttpClient, private appconfig: AppConfigService) {
        this.APIURL = appconfig.config().servicesBaseUrl;
    }

...

app-config.json

{
    "servicesBaseUrl": "http://...."
}

the application works perfect but the tests fail all because they do not recognize the url