Flutter Integration Testing

Flutter Integration Testing That Catches Real Bugs

Core Principle

Integration tests verify that components work TOGETHER correctly. Unit tests prove functions work in isolation. Integration tests prove THE SYSTEM works.

When to Use Integration vs Unit Tests

Flutter-Specific Patterns

Pattern 1: Widget Test with Real Providers

testWidgets('favorite button toggles and persists', (tester) async {
  final fakePrefs = FakeSharedPreferences();
  
  await tester.pumpWidget(
    ProviderScope(
      overrides: [
        sharedPreferencesProvider.overrideWithValue(fakePrefs),
      ],
      child: MaterialApp(home: StopDetailPage(stop: testStop)),
    ),
  );
  
  // Verify initial state: not favorited
  expect(find.byIcon(Icons.favorite_border), findsOneWidget);
  
  // Act: tap favorite
  await tester.tap(find.byIcon(Icons.favorite_border));
  await tester.pumpAndSettle();
  
  // Assert: icon changed AND data persisted
  expect(find.byIcon(Icons.favorite), findsOneWidget);
  expect(fakePrefs.getStringList('favorites'), contains(testStop.id));
});

Bug this catches: UI updates but data doesn't persist (or vice versa).

Pattern 2: Navigation Integration Test

testWidgets('tapping map link navigates to map page', (tester) async {
  await tester.pumpWidget(
    ProviderScope(
      child: MaterialApp.router(routerConfig: appRouter),
    ),
  );

  // Navigate to AI assistant
  await tester.tap(find.text('AI 助手'));
  await tester.pumpAndSettle();

  // Simulate map link tap
  // Find the MarkdownBody and trigger onTapLink
  final markdownFinder = find.byType(MarkdownBody);
  // ... trigger link callback

  await tester.pumpAndSettle();

  // Assert: now on map page
  expect(find.byType(MapPage), findsOneWidget);
});

Pattern 3: Async Provider Integration

testWidgets('loading → data → display flow', (tester) async {
  final fakeRepo = FakeVehicleRepository();
  
  await tester.pumpWidget(
    ProviderScope(
      overrides: [
        vehicleRepoProvider.overrideWithValue(fakeRepo),
      ],
      child: MaterialApp(home: MapPage()),
    ),
  );

  // Initially shows loading
  expect(find.byType(CircularProgressIndicator), findsOneWidget);
  
  // Simulate data arrival
  fakeRepo.emitVehicles(testVehicles);
  await tester.pumpAndSettle();
  
  // Shows data
  expect(find.byType(CircularProgressIndicator), findsNothing);
  expect(find.text('車號 ABC-123'), findsOneWidget);
});

Pattern 4: Error State Integration

testWidgets('API failure shows error UI with retry', (tester) async {
  final fakeRepo = FakeVehicleRepository();
  
  await tester.pumpWidget(testApp(fakeRepo));
  
  // Simulate error
  fakeRepo.emitError(Exception('Server 500'));
  await tester.pumpAndSettle();
  
  // Shows error message (not raw exception)
  expect(find.text('Server 500'), findsNothing);  // No raw error
  expect(find.textContaining('暫時無法'), findsOneWidget);
  
  // Retry button works
  fakeRepo.willSucceedNext = true;
  await tester.tap(find.text('重試'));
  await tester.pumpAndSettle();
  
  expect(find.byType(CircularProgressIndicator), findsNothing);
  expect(find.textContaining('資料已更新'), findsOneWidget);
});

Pattern 5: E2E CRUD Flow

testWidgets('full CRUD: add → view → edit → delete favorite', (tester) async {
  await tester.pumpWidget(testApp());
  
  // CREATE
  await tester.tap(find.byIcon(Icons.favorite_border).first);
  await tester.pumpAndSettle();
  expect(find.byIcon(Icons.favorite), findsOneWidget);
  
  // READ - navigate to favorites
  await tester.tap(find.text('設定'));
  await tester.pumpAndSettle();
  await tester.tap(find.text('我的收藏'));
  await tester.pumpAndSettle();
  expect(find.text(testStop.name), findsOneWidget);
  
  // DELETE
  await tester.tap(find.byIcon(Icons.delete).first);
  await tester.pumpAndSettle();
  expect(find.text(testStop.name), findsNothing);
});

Integration Test Structure

// test/e2e/feature_name_test.dart

import 'package:flutter_test/flutter_test.dart';

// Helper to create test app with all required overrides
Widget testApp({List<Override>? extraOverrides}) {
  return ProviderScope(
    overrides: [
      // Always override external dependencies
      sharedPreferencesProvider.overrideWithValue(FakeSharedPreferences()),
      locationServiceProvider.overrideWithValue(FakeLocationService()),
      ...?extraOverrides,
    ],
    child: MaterialApp.router(
      routerConfig: appRouter,
      localizationsDelegates: AppLocalizations.localizationsDelegates,
      supportedLocales: AppLocalizations.supportedLocales,
    ),
  );
}

What to Test in Integration (Bug-Finding Priority)

1. Cross-widget data flow — Provider state → Widget display
2. Navigation with parameters — Route params arrive correctly
3. User interaction sequences — Multi-step flows that exercise real paths
4. Error recovery — Error state → retry → success
5. State persistence — Data survives page navigation
6. Responsive layout — Key UI works at different screen sizes

Anti-Patterns to AVOID

❌ Over-Mocking in Integration Tests

// BAD: Everything is mocked — you're testing nothing real
testWidgets('page loads', (tester) async {
  await tester.pumpWidget(
    ProviderScope(
      overrides: [
        dataProvider.overrideWithValue(AsyncData(mockData)),
        // 10 more overrides...
      ],
      child: MockPage(), // Even the page is mocked!
    ),
  );
  expect(find.text('mock'), findsOneWidget); // Tests mock, not app
});

❌ No pumpAndSettle After State Change

// BAD: Assertions before widget tree rebuilds
await tester.tap(find.byIcon(Icons.add));
// Missing: await tester.pumpAndSettle();
expect(find.text('Added'), findsOneWidget); // FLAKY!

❌ Testing Widget Existence Without Behavior

// BAD: Only checks widget tree, not behavior
expect(find.byType(ElevatedButton), findsOneWidget);
// So what? Does the button DO anything?

// GOOD: Test the button works
await tester.tap(find.byType(ElevatedButton));
await tester.pumpAndSettle();
expect(someStateChanged, isTrue);

Localization in Tests

Always include localization delegates for widget tests that render localized text:

MaterialApp(
  localizationsDelegates: AppLocalizations.localizationsDelegates,
  supportedLocales: AppLocalizations.supportedLocales,
  home: PageUnderTest(),
)

Verification Checklist

• Tests exercise real user flows (not just render checks)
• External deps (network, DB, GPS) are faked, not the components under test
• Error states tested (not just happy path)
• Navigation tested with parameter passing
• Async loading states verified (loading → data → error)
• No flaky time-dependent assertions
• All tests pass: fvm flutter test

Related skills

• integration-testing-dart — DISAMBIGUATION: integration-testing-dart covers multi-module Dart integration test patterns. flutter-integration-testing is Flutter-specific widget integration testing. Use flutter-integration-testing for Flutter widget tests; use integration-testing-dart for Dart module integration tests.
• test-driven-development — use TDD for integration test implementation.
• testing-anti-patterns — audit for mocking errors after integration tests pass.