how to test flutter widget that depends on data coming from provider

I need to test this widget which depends on user provider that has user data inside it

 @override
  Widget build(BuildContext context) {
    final _userProvider = Provider.of<User>(context);
    UserSerializer _user = _userProvider.user;

    return Scaffold(
      appBar: appBar(
          backTheme: true,
          context: context,
          title: widget.edit ? 'Edit Profile' : 'Profile'),

this is the provider class

class User with ChangeNotifier {
  final facebookLogin = FacebookLogin();

  UserSerializer _loadedUser;
  UserSerializer get user {
    return _loadedUser;
  }

my problem is that profile screen don't have parametre or even provider.value. then how to force data into _user variable to test rest of screen. this is how widgets get access to providers

@override
Widget build(BuildContext context) {
return MultiProvider(
    providers: [
        ChangeNotifierProvider(create: (context) => User()),
        ],