Test for FirebaseUser update

main.dart

import 'dart:async';

import 'package:firebase_auth/firebase_auth.dart';
import 'package:flutter/material.dart';

void main() {
  runApp(new MyApp());
}

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      title: 'Flutter Demo',
      theme: new ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: new MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => new _MyHomePageState();
}

final auth = FirebaseAuth.instance;

class _MyHomePageState extends State<MyHomePage> {
  String _displayName = "Old display name - should be changed";
  String _photoUrl = "Old photoUrl - should be changed to null";

  Future<Null> _ensureLoggedIn() async {
    await auth.signInAnonymously();
    UserUpdateInfo userUpdateInfo = new UserUpdateInfo()
      ..displayName = _displayName == "New display name" ? null : "New display name";
    await auth.updateProfile(userUpdateInfo);
    FirebaseUser firebaseUser = await auth.currentUser();
    _displayName = firebaseUser.displayName;
    _photoUrl = firebaseUser.photoUrl;
  }

  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        title: new Text(widget.title),
      ),
      body: new Center(
        child: new Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            new Text(_displayName??"Null"),
            new Text(_photoUrl??"Null"),
          ],
        ),
      ),
      floatingActionButton: new FloatingActionButton(
          child: new Icon(Icons.add),
          onPressed: () {
            _ensureLoggedIn();
            setState((){});
          }),
    );
  }
}