Images are not visible during flutter_driver tests

Question

When running UI tests with flutter driver the assets are not displayed on iPhone simulator. They are displayed when app is run in debug mode from VS Code.

I tried to reproduce it on the example project generated by flutter create -i swift -a kotlin --androidx --org com.example example but without success. I followed exactly the same process of introducing flutter_driver tests in both apps according to this article. Unfortunately, in my app the images are not shown, and in example app they appear just fine. I compared project.pbxproj and pubspec.yaml files and they look fine to me.

For instance my pubspec.yaml:

dev_dependencies:
  flutter_driver:
    sdk: flutter
  test: any
  flutter_test:
    sdk: flutter
  screenshots:

flutter:
  uses-material-design: true

  assets:
    - assets/lang/pl.json
    - assets/images/

Is there anything that can help me with this issue? What can I do to debug the problem?

Logs

Beware, this is a very long log output.

flutter drive --target=test_driver/app.dart --verbose

https://gist.github.com/orestesgaolin/861c4f191773ca152b400d97ced2daeb

Flutter doctor

flutter doctor -v

[✓] Flutter (Channel stable, v1.7.8+hotfix.4, on Mac OS X 10.14.6 18G87, locale pl-PL)
    • Flutter version 1.7.8+hotfix.4 at /Users/dominik/Library/flutter
    • Framework revision 20e59316b8 (6 weeks ago), 2019-07-18 20:04:33 -0700
    • Engine revision fee001c93f
    • Dart version 2.4.0


[✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
    • Android SDK at /Users/dominik/Library/Android/sdk
    • Android NDK location not configured (optional; useful for native profiling support)
    • Platform android-28, build-tools 28.0.3
    • ANDROID_SDK_ROOT = /Users/dominik/Library/Android/sdk
    • Java binary at: /Users/dominik/Library/Application Support/JetBrains/Toolbox/apps/AndroidStudio/ch-0/191.5791312/Android
      Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b49-5587405)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 10.3)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 10.3, Build version 10G8
    • CocoaPods version 1.7.5

[✓] iOS tools - develop for iOS devices
    • ios-deploy 1.9.4

[✓] Android Studio (version 3.5)
    • Android Studio at /Users/dominik/Library/Application Support/JetBrains/Toolbox/apps/AndroidStudio/ch-0/191.5791312/Android Studio.app/Contents
    • Flutter plugin version 37.1.1
    • Dart plugin version 183.6270
    • Java version OpenJDK Runtime Environment (build 1.8.0_202-release-1483-b49-5587405)

[✓] VS Code (version 1.37.1)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.3.0

[✓] Connected device (1 available)
    • iPhone Xs Max • C1A5534A-AE3A-4FB3-95F6-993E351FF2D3 • ios • com.apple.CoreSimulator.SimRuntime.iOS-12-4 (simulator)

• No issues found!

Answer 1

So the solution was to create separate main_test.dart file that wraps whole app in DefaultAssetBundle like so:

runApp(DefaultAssetBundle(
      bundle: TestAssetBundle(),
      child: App(),
    ));

and TestAssetBundle is like so:

class TestAssetBundle extends CachingAssetBundle {
  @override
  Future<String> loadString(String key, {bool cache = true}) async {
    final ByteData data = await load(key);
    if (data == null) throw FlutterError('Unable to load asset');
    return utf8.decode(data.buffer.asUint8List());
  }

  @override
  Future<ByteData> load(String key) async => rootBundle.load(key);
}

And in app.dart you have to reference correct file:

import 'package:flutter_driver/driver_extension.dart';
import 'package:playoo_league_player/main_test.dart' as app;

void main() {
  // This line enables the extension.
  enableFlutterDriverExtension();

  // Call the `main()` function of the app, or call `runApp` with
  // any widget you are interested in testing.
  app.main();
}

Full explanation can be found here: https://medium.com/@sardox.vl/flutter-test-and-randomly-missing-assets-in-goldens-ea959cdd336a