skills/flutter/references/advanced-testing.md

name	description
advanced-testing	Flutter testing - widget testing, integration testing, test utilities, and testing best practices

Testing

Flutter provides comprehensive testing tools for unit, widget, and integration tests.

Widget Testing

Test individual widgets in isolation.

import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('Counter increments when button is pressed', (WidgetTester tester) async {
    // Build widget
    await tester.pumpWidget(const MyApp());

    // Find widget
    expect(find.text('0'), findsOneWidget);
    expect(find.text('1'), findsNothing);

    // Tap button
    await tester.tap(find.byType(ElevatedButton));
    await tester.pump();

    // Verify result
    expect(find.text('0'), findsNothing);
    expect(find.text('1'), findsOneWidget);
  });
}

Finding Widgets

// Find by text
find.text('Hello')
find.textContaining('Hello')

// Find by type
find.byType(ElevatedButton)
find.byType(Text)

// Find by key
find.byKey(Key('my-key'))

// Find by icon
find.byIcon(Icons.star)

// Find by widget
find.byWidget(myWidget)

// Find ancestors/descendants
find.ancestor(of: find.text('Hello'), matching: find.byType(Container))
find.descendant(of: find.byType(Column), matching: find.text('Hello'))

Widget Tester Methods

// Pump widget
await tester.pumpWidget(MyWidget());

// Pump frames
await tester.pump(); // One frame
await tester.pump(Duration(seconds: 1)); // Multiple frames

// Tap
await tester.tap(find.byType(ElevatedButton));
await tester.tapAt(Offset(100, 100));

// Drag
await tester.drag(find.byType(ListView), Offset(0, -100));

// Enter text
await tester.enterText(find.byType(TextField), 'Hello');

// Long press
await tester.longPress(find.byType(ElevatedButton));

// Fling
await tester.fling(find.byType(ListView), Offset(0, -100), 1000);

Expectations

// Find widgets
expect(find.text('Hello'), findsOneWidget);
expect(find.text('Hello'), findsNothing);
expect(find.text('Hello'), findsWidgets);
expect(find.text('Hello'), findsNWidgets(2));

// Widget properties
final widget = tester.widget<Text>(find.text('Hello'));
expect(widget.style?.fontSize, 16);

// Widget exists
expect(find.byType(ElevatedButton), findsOneWidget);

Integration Testing

Test complete app flows.

import 'package:flutter_test/flutter_test.dart';
import 'package:integration_test/integration_test.dart';

void main() {
  IntegrationTestWidgetsFlutterBinding.ensureInitialized();

  testWidgets('Complete user flow', (WidgetTester tester) async {
    // Start app
    await tester.pumpWidget(const MyApp());
    await tester.pumpAndSettle();

    // Navigate
    await tester.tap(find.text('Login'));
    await tester.pumpAndSettle();

    // Enter credentials
    await tester.enterText(find.byKey(Key('email')), 'user@example.com');
    await tester.enterText(find.byKey(Key('password')), 'password');
    await tester.tap(find.text('Submit'));
    await tester.pumpAndSettle();

    // Verify navigation
    expect(find.text('Dashboard'), findsOneWidget);
  });
}

Mocking

Mock dependencies for testing.

// Mock HTTP client
class MockHttpClient extends Mock implements http.Client {}

void main() {
  testWidgets('Loads data from API', (WidgetTester tester) async {
    final mockClient = MockHttpClient();
    
    when(mockClient.get(any)).thenAnswer(
      (_) async => http.Response('{"data": "test"}', 200),
    );

    await tester.pumpWidget(
      MyApp(httpClient: mockClient),
    );
    
    await tester.pumpAndSettle();
    
    expect(find.text('test'), findsOneWidget);
  });
}

Golden Tests

Test widget appearance.

testWidgets('Widget appearance', (WidgetTester tester) async {
  await tester.pumpWidget(const MyWidget());
  
  await expectLater(
    find.byType(MyWidget),
    matchesGoldenFile('golden/my_widget.png'),
  );
});

Key Points

• Use testWidgets() for widget tests
• Use find to locate widgets
• Use tester.pumpWidget() to build widgets
• Use tester.pump() to advance frames
• Use expect() with findsOneWidget, findsNothing, etc.
• Use IntegrationTestWidgetsFlutterBinding for integration tests
• Mock dependencies for isolated testing
• Use golden tests for visual regression testing
• Use pumpAndSettle() to wait for animations to complete