I am encountering an issue when testing my Flutter widget, CitySearchButton. I want to verify that a CircularProgressIndicator is displayed when isLoading is true, but the test fails.

Problem Description:
I am testing the CitySearchButton widget, and I want to confirm that a CircularProgressIndicator is displayed when isLoading is true. However, the test does not pass.

Reproducible Code:

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:my_app/city_search_button.dart';
import 'package:mockito/mockito.dart';
import 'package:provider/provider.dart';

class MockViewModel extends Mock implements ViewModel {}

void main() {
  testWidgets('Displays CircularProgressIndicator when isLoading is true', (WidgetTester tester) async {
    // Setting up the Mock ViewModel
    final mockViewModel = MockViewModel();
    when(mockViewModel.state).thenReturn(CitySearchState(isLoading: true));

    // Setting up the Provider Container
    final container = ProviderContainer(
      overrides: [
        viewModelProvider.overrideWithValue(mockViewModel),
      ],
    );

    // Building the widget under test
    await tester.pumpWidget(UncontrolledProviderScope(
      container: container,
      child: const MaterialApp(
        home: Scaffold(
          body: CitySearchButton(),
        ),
      ),
    ));

    // Pumping again to reflect the state
    await tester.pump();

    // Debugging the widget tree
    debugDumpApp();

    // Verifying that CircularProgressIndicator is displayed
    expect(find.byType(CircularProgressIndicator), findsOneWidget);
  });
}

What I Have Tried:

• Used pumpAndSettle(), but the result did not change.
• Used debugDumpApp() to debug the widget tree, but the expected widget was not found.

Error Message:

══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following TestFailure was thrown running a test:
Expected: exactly one matching candidate
  Actual: _TypeWidgetFinder:<Found 0 widgets with type "CircularProgressIndicator": []>
   Which: means none were found but one was expected

When the exception was thrown, this was the stack:
#4      main.<anonymous closure>.<anonymous closure> (file:///Users/username/Flutter/weather_app/test/components/city_search_button_test.dart:64:7)
<asynchronous suspension>
#5      testWidgets.<anonymous closure>.<anonymous closure> (package:flutter_test/src/widget_tester.dart:168:15)
<asynchronous suspension>
#6      TestWidgetsFlutterBinding._runTestBody (package:flutter_test/src/binding.dart:1013:5)
<asynchronous suspension>
<asynchronous suspension>
(elided one frame from package:stack_trace)

This was caught by the test expectation on the following line:
# file:///Users/username/Flutter/weather_app/test/components/city_search_button_test.dart line 64
The test description was:
  Displays CircularProgressIndicator when isLoading is true
════════════════════════════════════════════════════════════════════════════════════════════════════

Mock ViewModel Setup:

class MockViewModel extends Mock implements ViewModel {}

final mockViewModel = MockViewModel();
when(mockViewModel.state).thenReturn(CitySearchState(isLoading: true));

Provider Container Setup:

final container = ProviderContainer(
  overrides: [
    viewModelProvider.overrideWithValue(mockViewModel),
  ],
);

Environment:

• Flutter 3.16.3

Additional Information:

• flutter_riverpod: ^2.5.1
• mockito: ^5.4.4

Any help would be greatly appreciated. Thank you!

What Did You Try?

• I used pumpAndSettle() to ensure all animations and state changes were settled before checking for the CircularProgressIndicator.
• I used debugDumpApp() to inspect the widget tree and confirmed that the expected state was not reflected.

What Were You Expecting?

• I expected CircularProgressIndicator to be present in the widget tree when isLoading is set to true in the CitySearchState.
• I expected the debugDumpApp() output to include the CircularProgressIndicator widget, indicating that the loading state was correctly handled by the CitySearchButton.