anchor.diff:    Future<String> _message = new Future<String>.value('');
   
     Future<String> _testSignInAnonymously() async {
  -    FirebaseUser user = await auth.signInAnonymously();
  +    FirebaseUser user = await _auth.signInAnonymously();
       assert(user != null);
  -    assert(user == auth.currentUser);
  +    assert(user == _auth.currentUser);
       assert(user.isAnonymous);
       assert(!user.isEmailVerified);
       if (Platform.isIOS) {
  
positive.code:   }
  
    Future<String> _testSignInWithGoogle() async {
      GoogleSignInAccount googleUser = await googleSignIn.signIn();
      GoogleSignInAuthentication googleAuth = await googleUser.authentication;
      FirebaseUser user = await auth.signInWithGoogle(
        accessToken: googleAuth.accessToken,
        idToken: googleAuth.idToken,
      );
  
negative.code: import 'package:firebase_auth/firebase_auth.dart';
  import 'package:google_sign_in/google_sign_in.dart';
  
  final FirebaseAuth _auth = FirebaseAuth.instance;
  final GoogleSignIn _googleSignIn = new GoogleSignIn();
  
  void main() {
    runApp(new MyApp());
  