Flutter Mocktail : <type 'Future<PermissionStatus>' is not a subtype of type 'Permissions'>

Question

I'm trying to mock the background_downloader package , specifically this line in my class I'm trying to mock:

var status = await fileDownloader.permissions.status(permissionType);

I keep getting error message:

Here is my Test class:

class MockFileDownloader extends Mock implements FileDownloader {}

void main() {
  late MockFileDownloader mockFileDownloader;

  setUp(() {});

  tearDown(() {});

  group('BkgrdFileTransferBloc : _initBackgroundFileTransfer() ', () {
    setUp(() {
      SharedPreferences.setMockInitialValues({BackgroundFileTransfer.notificationDlgShownPref: false});

      mockFileDownloader = MockFileDownloader();

      var testBasedownloader = FileDownloader().downloaderForTesting;
      var permissionService = testBasedownloader.permissionsService;
      
      ///these lines here, I'm having issues with
      when(() => mockFileDownloader.permissions).thenReturn(permissionService);
      when(() => mockFileDownloader.permissions.status(PermissionType.notifications)).thenAnswer((_) async => PermissionStatus.denied);
      
    });
    blocTest(
      'should show notificationNotGrantedWarning - notificationDlgShownPref = false,   ',
      build: () {
        return BkgrdFileTransferBloc(mockFileDownloader);
      },
      act: (bloc) => bloc.add(BkgrdFilesTransferEvent.initialize(DownloadTask(url: ''))),
      expect:
          () => [
            TypeMatcher<BkgrdFileTransferState>()
                .having((bkgrdFileTransferState) => bkgrdFileTransferState.notificationNotGrantedWarning, 'notificationNotGrantedWarning', isTrue)
                .having((bkgrdFileTransferState) => bkgrdFileTransferState.task, 'task', isNotNull),
          ],
    );
  });
}

Albert221 · Accepted Answer · 2025-04-18 09:44:55Z

1

You can do

when(() => mockFileDownloader.permissions).thenReturn(permissionService);

but you cannot do

when(() => mockFileDownloader.permissions.status(PermissionType.notifications)).thenAnswer((_) async => PermissionStatus.denied);

because mockFileDownloader.permissions is already a permissionService. You would need to also create a mock of the permission service, mock its status method and then return it from the mockFileDownloader.permissions mock.

class MockPermissionsService extends Mock implements PermissionsService {}

final permissionsService = MockPermissionsService();
when(() => permissionsService.status(PermissionType.notifications)).thenAnswer((_) async => PermissionStatus.denied);

when(() => mockFileDownloader.permissions).thenReturn(permissionService);

answered Apr 18 at 9:44

Albert221

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1 Comment

Mike6679 Apr 18 at 20:16

I think thats the problem ......the 3rd party package: "background_downloader" does not export / expose "PermissionsService" class so I cannot mock it

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Flutter Mocktail : <type 'Future<PermissionStatus>' is not a subtype of type 'Permissions'>

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Here is my Test class:

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I keep getting error message:

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