Fail to inject mock service into root component during unit testing

It seems there’s no way to tell Ionic to use a mock service to create a root component. There’s no way to provide the information regarding the mock service throughIonicModule.forRoot(root, config, deeplink).

My test code looks like this:

beforeEach(async(() => {
    TestBed.configureTestingModule({
        declarations: [MyApp, LocationPage],
        providers: [
            {provide: RealService, useClass: MockService}
        ],
        imports: [IonicModule.forRoot(MyApp)]
    }).compileComponents().then(() => {
        fixture = TestBed.createComponent(MyApp);
        comp =  fixture.componentInstance;
    });
}));

The provider information is hard-coded in IonicModule.forRoot (the following code was taken from Ionic 2 src code):

IonicModule.forRoot = function (appRoot, config, deepLinkConfig) {
    if (config === void 0) { config = null; }
    if (deepLinkConfig === void 0) { deepLinkConfig = null; }
    return {
        ngModule: IonicModule,
        providers: [
            // useValue: bootstrap values
            { provide: AppRootToken, useValue: appRoot },
            { provide: ConfigToken, useValue: config },
            { provide: DeepLinkConfigToken, useValue: deepLinkConfig },
            // useFactory: user values
            { provide: PlatformConfigToken, useFactory: providePlatformConfigs },
            // useFactory: ionic core providers
            { provide: Platform, useFactory: setupPlatform, deps: [DOCUMENT, PlatformConfigToken, NgZone] },
            { provide: Config, useFactory: setupConfig, deps: [ConfigToken, Platform] },
            // useFactory: ionic app initializers
            { provide: APP_INITIALIZER, useFactory: registerModeConfigs, deps: [Config], multi: true },
            { provide: APP_INITIALIZER, useFactory: registerTransitions, deps: [Config], multi: true },
            { provide: APP_INITIALIZER, useFactory: setupProvideEvents, deps: [Platform, DomController], multi: true },
            { provide: APP_INITIALIZER, useFactory: setupTapClick, deps: [Config, Platform, DomController, App, NgZone, GestureController], multi: true },
            // useClass
            { provide: HAMMER_GESTURE_CONFIG, useClass: IonicGestureConfig },
            // useValue
            { provide: ANALYZE_FOR_ENTRY_COMPONENTS, useValue: appRoot, multi: true },
            // ionic providers
            ActionSheetController,
            AlertController,
            App,
            DomController,
            Events,
            Form,
            GestureController,
            Haptic,
            Keyboard,
            LoadingController,
            Location,
            MenuController,
            ModalController,
            PickerController,
            PopoverController,
            TapClick,
            ToastController,
            TransitionController,
            { provide: LocationStrategy, useFactory: provideLocationStrategy, deps: [PlatformLocation, [new Inject(APP_BASE_HREF), new Optional()], Config] },
            { provide: UrlSerializer, useFactory: setupUrlSerializer, deps: [DeepLinkConfigToken] },
            { provide: DeepLinker, useFactory: setupDeepLinker, deps: [App, UrlSerializer, Location] },
        ]
    };
};

Can someone from Ionic team please provide an answer?