anchor.diff:  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();
  +final FirebaseAuth _auth = FirebaseAuth.instance;
  +final GoogleSignIn _googleSignIn = new GoogleSignIn();
   
   void main() {
     runApp(new MyApp());
  
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:   Future<String> _message = new Future<String>.value('');
  
    Future<String> _testSignInAnonymously() async {
      FirebaseUser user = await _auth.signInAnonymously();
      assert(user != null);
      assert(user == _auth.currentUser);
      assert(user.isAnonymous);
      assert(!user.isEmailVerified);
      if (Platform.isIOS) {
  