Creating a Mock stops debugger from working in flutter application

[themizzi]

In a simple app, if you import mockito into a flutter application test and then create any mock class (don't even have to use it) using extends Mock the debugger will no longer stop at any breakpoints in non-test code. This has caused us a number of headaches. If there is anything I can do to help, please let me know.

[srawlins]

That's a bizarre bug. Can you show me the exact code that creates this bug? class X ... and maybe new X();...?

Can you show me the output of flutter doctor?

[themizzi]

Here's a sample I put together. All I have to do in the test file at the bottom is remove the class MockNoteListModel extends Mock implements NoteListModel {} line and the debugger starts working again. I never even call new on it. Note, the debugger will always stop on breakpoints in the test file and can even step into the app file; however, a breakpoint in the app file is never stopped at on its own and in code/studio it shows that the breakpoint will not be hit after the test begins. I notice there is some bootstrap code in a few of the files in the library so my best guess is something there is causing the problem once the code is loaded up after using extends Mock maybe mixing with something weird I do not understand. I didn't add a lot here, certainly not anything out of the ordinary, so I'm a little stumped. On a totally blank project, it does work with the default test, so something in here mixing with mockito seems to be causing the issue. Tested in latest versions of vscode and android studio. Flutter 1.22.0. We have this problem across our team on a large project our team is working on so I am going to have some folks test on their machines tomorrow to make sure it's not something specific to my setup.

here's main.dart:

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';

void main() {
  runApp(
    MyApp(),
  );
}

abstract class HomeRouteFactory {
  Route call();
}

class MyApp extends StatelessWidget {
  final HomeRouteFactory myAppHomePageRouteFactory;

  const MyApp({
    Key key,
    this.myAppHomePageRouteFactory,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      onGenerateRoute: (settings) {
        return MaterialPageRoute(
          builder: (context) {
            return NotesListPage(
              notesValueListenable: ValueNotifier<List<NoteListModel>>([]),
            );
          },
        );
      },
    );
  }
}

abstract class NoteListModel {
  String get title;

  String get id;
}

class NotesListPage extends StatelessWidget {
  final ValueListenable<List<NoteListModel>> notesValueListenable;

  const NotesListPage({
    this.notesValueListenable,
  });

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Notes'),
      ),
      body: ValueListenableBuilder<List<NoteListModel>>(
        valueListenable:
            notesValueListenable ?? ValueNotifier<List<NoteListModel>>([]),
        builder: (context, notes, child) {
          return Visibility(
            visible: notes != null,
            replacement: Center(child: CircularProgressIndicator()),
            child: ListView.separated(
              itemBuilder: (context, index) {
                return ListTile(
                  title: Text(notes[index]?.title ?? ''),
                );
              },
              separatorBuilder: (context, index) => Divider(),
              itemCount: notesValueListenable?.value?.length ?? 0,
            ),
          );
        },
      ),
    );
  }
}

and main_test.dart:

import 'package:flutter/material.dart';
import 'package:flutter_notes/main.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:mockito/mockito.dart';

class StubNoteListModel implements NoteListModel {
  final String title;
  final String id;

  StubNoteListModel({this.title, this.id});
}

class MockNoteListModel extends Mock implements NoteListModel {}

void main() {
  group('Note List Page', () {
    testWidgets('it shows list of notes', (WidgetTester tester) async {
      // GIVEN
      final note1 = StubNoteListModel();
      final note2 = StubNoteListModel();
      final notesValuesNotifier = ValueNotifier<List<NoteListModel>>([
        note1,
        note2,
      ]);

      // WHEN
      await tester.pumpWidget(
        MaterialApp(
          home: NotesListPage(
            notesValueListenable: notesValuesNotifier,
          ),
        ),
      );

      // THEN
      expect(find.byType(ListTile), findsNWidgets(2));
    });
  });
}

pubspec.yaml:

name: flutter_notes
description: A new Flutter project.

# The following line prevents the package from being accidentally published to
# pub.dev using `pub publish`. This is preferred for private packages.
publish_to: 'none' # Remove this line if you wish to publish to pub.dev

# The following defines the version and build number for your application.
# A version number is three numbers separated by dots, like 1.2.43
# followed by an optional build number separated by a +.
# Both the version and the builder number may be overridden in flutter
# build by specifying --build-name and --build-number, respectively.
# In Android, build-name is used as versionName while build-number used as versionCode.
# Read more about Android versioning at https://developer.android.com/studio/publish/versioning
# In iOS, build-name is used as CFBundleShortVersionString while build-number used as CFBundleVersion.
# Read more about iOS versioning at
# https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
version: 1.0.0+1

environment:
  sdk: ">=2.7.0 <3.0.0"

dependencies:
  flutter:
    sdk: flutter

  # The following adds the Cupertino Icons font to your application.
  # Use with the CupertinoIcons class for iOS style icons.
  cupertino_icons: ^0.1.3

dev_dependencies:
  flutter_test:
    sdk: flutter
  mockito: ^4.0.0
  integration_test: ^0.9.1

# For information on the generic Dart part of this file, see the
# following page: https://dart.dev/tools/pub/pubspec

# The following section is specific to Flutter.
flutter:

  # The following line ensures that the Material Icons font is
  # included with your application, so that you can use the icons in
  # the material Icons class.
  uses-material-design: true

  # To add assets to your application, add an assets section, like this:
  # assets:
  #   - images/a_dot_burr.jpeg
  #   - images/a_dot_ham.jpeg

  # An image asset can refer to one or more resolution-specific "variants", see
  # https://flutter.dev/assets-and-images/#resolution-aware.

  # For details regarding adding assets from package dependencies, see
  # https://flutter.dev/assets-and-images/#from-packages

  # To add custom fonts to your application, add a fonts section here,
  # in this "flutter" section. Each entry in this list should have a
  # "family" key with the font family name, and a "fonts" key with a
  # list giving the asset and other descriptors for the font. For
  # example:
  # fonts:
  #   - family: Schyler
  #     fonts:
  #       - asset: fonts/Schyler-Regular.ttf
  #       - asset: fonts/Schyler-Italic.ttf
  #         style: italic
  #   - family: Trajan Pro
  #     fonts:
  #       - asset: fonts/TrajanPro.ttf
  #       - asset: fonts/TrajanPro_Bold.ttf
  #         weight: 700
  #
  # For details regarding fonts from package dependencies,
  # see https://flutter.dev/custom-fonts/#from-packages

[themizzi]

Here's another quick piece of crazy info, if I change the mock to:

class MockNoteListModel extends Mock implements ValueNotifier {}

any internal class to dart/flutter sdk and it starts working again.

[themizzi]

also here is flutter doctor, almost forgot:

[✓] Flutter (Channel stable, 1.22.0, on Mac OS X 10.15.7 19H2, locale en-US)
    • Flutter version 1.22.0 at /Users/themizzi/.asdf/installs/flutter/1.22.0-stable
    • Framework revision d408d302e2 (7 days ago), 2020-09-29 11:49:17 -0700
    • Engine revision 5babba6c4d
    • Dart version 2.10.0

[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
    • Android SDK at /Users/themizzi/Library/Android/sdk
    • Platform android-29, build-tools 29.0.2
    • Java binary at: /Users/themizzi/Library/Application Support/JetBrains/Toolbox/apps/AndroidStudio/ch-0/193.6821437/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 12.0.1)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 12.0.1, Build version 12A7300
    • CocoaPods version 1.9.3

[✓] Android Studio (version 4.0)
    • Android Studio at /Users/themizzi/Library/Application Support/JetBrains/Toolbox/apps/AndroidStudio/ch-0/193.6821437/Android Studio.app/Contents
    • Flutter plugin version 50.0.1
    • Dart plugin version 193.7547
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)

[✓] VS Code (version 1.49.3)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.15.0

[✓] Connected device (1 available)
    • sdk gphone x86 64 (mobile) • emulator-5554 • android-x64 • Android 11 (API 30) (emulator)
    ! Error: iPhone is not connected. Xcode will continue when iPhone is connected. (code -13)

• No issues found!