[question] how to test a bloc listener

[aoatmon]

use case

I would like to structure my tests in a way that allow me to

• test listeners on cubit change
• rely on underlying provider for dependency injections in listeners and cubit
• test general context changes on cubit change (example navigation)

issue

afaik the typical implementation for this is a full blown widget test which may be undesirable when we don't actually need to test the widgets.

I'm trying to streamline the process, so far with mixed results

(if you want to run the code you can just clone the repo)

code

```dart import 'dart:async'; import 'package:flutter/material.dart'; import 'package:flutter_bloc/flutter_bloc.dart'; import 'package:flutter_test/flutter_test.dart' as test; import 'mocks.dart'; typedef ContextTester = FutureOr Function( BuildContext context, test.WidgetTester tester, ); extension BlocProviderGenetator on Cubit { BlocProvider> get provider => BlocProvider( create: (context) => this, ); } extension BlocListProviderGenetator on Iterable { Iterable get providers sync* { for (final cubit in this) { yield cubit.provider; } } } void cubitContextTester({ Iterable listeners = const [], Iterable cubits = const [], Iterable repositories = const [], required String title, required ContextTester contextBlocTest, }) => contextTester( title: title, tester: contextBlocTest, build: (key) => MultiRepositoryProvider( providers: [EmptyRepository(), ...repositories], child: Builder( builder: (context) => MultiBlocProvider( providers: [ ...[EmptyCubit(), ...cubits].providers ], child: Builder( builder: (context) => MultiBlocListener( listeners: [EmptyCubitListener(), ...listeners], child: Builder( builder: (context) => MaterialApp(home: SizedBox(key: key)), ), ), ), ), ), ), ); void contextTester({ required String title, required Widget Function(Key) build, required ContextTester tester, }) { final key = UniqueKey(); test.testWidgets(title, (_tester) async { await _tester.pumpWidget(build(key)); final context = _tester.element(test.find.byKey(key)); await tester(context, _tester); }); } ///? source `https://github.com/felangel/bloc/blob/master/packages/bloc_test/lib/src/bloc_test.dart#L176` ///! modified ContextTester contextBlocTest, State>({ FutureOr Function(BuildContext)? setUp, required B Function(BuildContext) build, State Function(BuildContext)? seed, Function(B bloc)? act, Duration? wait, int? skip, dynamic Function(BuildContext)? expect, Function(B bloc)? verify, dynamic Function()? errors, FutureOr Function(BuildContext)? tearDown, }) { return (context, tester) async { final unhandledErrors =

[aoatmon]

sorry for the wrong label :/

[felangel]

Hi @aoatmon 👋 Thanks for opening an issue!

I'm not sure I understand what you're trying to achieve. If you want to test your widget code (including providing blocs/cubits) then I highly recommend you use a widget test. If you want to test your blocs/cubits alone then I highly recommend you use bloc_test.

I recommend taking a look at the counter example (it includes unit, widget, and integration tests).

Hope that helps 👍

[aoatmon]

hi @felangel I'm not trying to test a widget, but to

• verify the interaction between cubit and listeners
• verify that a listener interact with context (example providers context.read<Foo>()) my current not working solution uses testWidgets

void contextTester({
  required String title,
  required Widget Function(Key) build,
  required ContextTester tester,
}) {
  final key = UniqueKey();
  test.testWidgets(title, (_tester) async {
    await _tester.pumpWidget(build(key));
    final context = _tester.element(test.find.byKey(key));
    await tester(context, _tester);
  });
}

but it fails to find widget in the context (I'm aware the logs point more at a provider issue) but my question is more open ended than "please fix my errors"

I'm trying to find a consistent way to test this aspect of the package

[felangel]

@aoatmon BlocListener and BlocProvider are widgets so I highly recommend using testWidgets as illustrated in the example I shared above.

To verify the interaction between cubits and listeners you can provide a mock cubit to the widget tree and use whenListen from package:bloc_test to stub the state stream.

To verify that a listener interacts with the context you can again provided a mock instance of the bloc or cubit and verify the correct API is called via verify from package:mocktail.

You can refer to the weather example tests for a complete example of what I described/recommend.

Hope that helps 👍

[aoatmon]

I put together this

new sample

```dart import 'dart:async'; import 'package:flutter/material.dart'; import 'package:flutter_bloc/flutter_bloc.dart'; import 'package:flutter_test/flutter_test.dart'; import 'package:go_router/go_router.dart'; import 'package:mocktail/mocktail.dart'; import 'package:bloc_route_test/src/shared/all.dart'; import '../mocks/all.dart'; void routelistenerTest, S>( String description, { required GoRouterBlocListener Function(B, GoRouter) buildListener, required B Function() buildCubit, required void Function(B) act, required String location, Duration? timeout, }) async { if (timeout != null) { Future.delayed(timeout, () => throw Exception('timeout')); } runZonedGuarded( () => testWidgets( description, (tester) async { const key = ValueKey('SizedBox'); final cubit = buildCubit(); final router = MockRouter(); when(() => router.go(location)).thenAnswer((_) { return; }); await tester.pumpWidget(MaterialApp( home: const SizedBox(key: key), builder: (context, app) => MultiBlocListener( listeners: [buildListener(cubit, router)], child: app!, ), )); final _ = tester.element(find.byKey(key)); act(cubit); await cubit.close(); verify(() => router.go(location)).called(1); }, ), (e, s) => throw Exception(e), ); } ```

it works, but I'm not sure I'm using this package as intended I would appreciate if someone could tell me if I'm doing something wrong

[felangel]

@aoatmon if it works for you feel free to keep using that approach but as I mentioned, I recommend following the patterns found in the examples. I can't provide much feedback because I don't feel I have enough context and there are objects like GoRouterBlocListener which are not part of the bloc library.

Closing for now but if you have any other questions that pertain to packages in the bloc library and the recommended usage, then I'm happy to continue the conversation 👍