anchor.diff:    }
   
     Future<String> _testSignInWithGoogle() async {
  -    GoogleSignInAccount googleUser = await googleSignIn.signIn();
  +    GoogleSignInAccount googleUser = await _googleSignIn.signIn();
       GoogleSignInAuthentication googleAuth = await googleUser.authentication;
  -    FirebaseUser user = await auth.signInWithGoogle(
  +    FirebaseUser user = await _auth.signInWithGoogle(
         accessToken: googleAuth.accessToken,
         idToken: googleAuth.idToken,
       );
  
positive.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) {
  
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());
  