Flutter widget test mockito error type Null is not a subtype of bool

So I am writing widget testing for Flutter using flutter test plugin. So, in my test widget, I am using mockito to mock third party services. So, I am getting an error that says 'type Null is not a subtype of bool'. I tried to cover for that but I do not get why am I still getting the error when I run the test code.

I tried to cover for that but I do not get why am I still getting the error when I run the test code. Here is my code below:

class MockGlobalSearchViewModel extends Mock implements GlobalSearchViewModel {}

@GenerateMocks([MockGlobalSearchViewModel])

testWidgets('Global Widget Test', (WidgetTester tester) async {
    // Create mock instances
    final mockGlobalSearchViewModel = MockGlobalSearchViewModel();
   

    when(mockGlobalSearchViewModel.isNetworkError()).thenReturn(true);//this is where I am getting the error

        final globalSearchViewModelProvider = Provider<GlobalSearchViewModel>.value(value: mockGlobalSearchViewModel);

 await tester.pumpWidget(
      MaterialApp(
        home: MultiProvider(
          providers: [
            globalSearchViewModelProvider,
     
          ],
          child: const GlobalSearchWidget()

So, can I please have some assistance from anyone, I honestly tried anything and I cannot get why am I not getting it right.

Solution

Problem:

You're getting the error because the mocks for GlobalSearchViewModel has not been generated. Mockito uses code generation to create its mocks.

Solution:

To generate the mocks for GlobalSearchViewModel, do the following:

Remove the manually written mock from your test file:

class MockGlobalSearchViewModel extends Mock implements GlobalSearchViewModel {}

Add the build_runner package to your project's dev dependencies:
```
dart pub add dev:build_runner
```

Import the generated mocks file and annotate it with @GenerateMocks:

@GenerateMocks([GlobalSearchViewModel])
import 'test_file_name.mocks.dart'; // Replace `test_file_name` with your test file name

Run build_runner to generate the mocks file:
```
dart run build_runner build
```
Run your tests and the "Null is not a subtype of bool" error should not up.
```
flutter test
```