Example not working #17074

Steps to Reproduce

I installed the package, copy paste the exact code snippet in the Example, run on both Emulator (Nexus 2 API 27) and my Samsung S8 (Android 8).

After choosing an existing account or logging in with new account, the app returns to the first screen with the button "Sign in"

Logs

flutter run output

Launching lib/main.dart on SM G950U1 in debug mode...
Initializing gradle... 0.5s
Resolving dependencies... 0.6s
Running 'gradlew assembleDebug'... 1.9s
Built build/app/outputs/apk/debug/app-debug.apk (33.3MB).
I/FlutterActivityDelegate(27473): onResume setting current activity to this
Syncing files to device SM G950U1... 1.9s

flutter analyze output

Analyzing /home/minhtriet/playground/flutter/google_login_example...
error • The constructor returns type 'dynamic' that isn't of expected type 'Widget' at test/widget_test.dart:15:29 • strong_mode_invalid_cast_new_expr
error • Undefined class 'MyApp' at test/widget_test.dart:15:33 • undefined_class
hint • Unused import: 'package:google_login_example/main.dart' at test/widget_test.dart:10:8 • unused_import
3 issues found.
(Ran in 5.0s)

Flutter Doctor

flutter doctor -v output

[✓] Flutter (Channel beta, v0.2.8, on Linux, locale en_US.UTF-8)
• Flutter version 0.2.8 at /home/minhtriet/software/flutter
• Framework revision b397406 (4 weeks ago), 2018-04-02 13:53:20 -0700
• Engine revision c903c21
• Dart version 2.0.0-dev.43.0.flutter-52afcba357

[✓] Android toolchain - develop for Android devices (Android SDK 27.0.3)
• Android SDK at /home/minhtriet/Android/Sdk
• Android NDK location not configured (optional; useful for native profiling support)
• Platform android-27, build-tools 27.0.3
• Java binary at: /home/minhtriet/software/android-studio/jre/bin/java
• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)
• All Android licenses accepted.

[✓] Android Studio (version 3.1)
• Android Studio at /home/minhtriet/software/android-studio
• Java version OpenJDK Runtime Environment (build 1.8.0_152-release-1024-b01)

[!] IntelliJ IDEA Ultimate Edition (version 2018.1)
• IntelliJ at /home/minhtriet/software/idea-IU-181.4203.550
✗ Flutter plugin not installed; this adds Flutter specific functionality.
✗ Dart plugin not installed; this adds Dart specific functionality.
• For information about installing plugins, see
https://flutter.io/intellij-setup/#installing-the-plugins

[!] VS Code (version 1.19.1)
• VS Code at /usr/share/code
• Dart Code extension not installed; install from
https://marketplace.visualstudio.com/items?itemName=Dart-Code.dart-code

[✓] Connected devices (1 available)
• SM G950U1 • 988820315651584756 • android-arm64 • Android 8.0.0 (API 26)

! Doctor found issues in 2 categories.