flutter-testing

Flutter Testing Best Practices

Comprehensive testing strategies for Flutter apps across unit, widget, and integration levels.

1. Widget Testing (flutter_test)

Use testWidgets to render UI components in an isolated test environment without a physical device or emulator.

import 'package:flutter_test/flutter_test.dart';
import 'package:flutter/material.dart';
import 'package:myapp/ui/counter_widget.dart';

void main() {
  testWidgets('Counter increments smoke test', (WidgetTester tester) async {
    // 1. Pump the widget inside a MaterialApp
    await tester.pumpWidget(
      const MaterialApp(home: Scaffold(body: CounterWidget())),
    );

    // 2. Verify initial state
    expect(find.text('0'), findsOneWidget);
    expect(find.text('1'), findsNothing);

    // 3. Perform tap interaction
    await tester.tap(find.byIcon(Icons.add));
    await tester.pump(); // Trigger frame redraw

    // 4. Verify updated state
    expect(find.text('0'), findsNothing);
    expect(find.text('1'), findsOneWidget);
  });
}

Key Tester Methods

• tester.pumpWidget(widget): Renders the given widget tree.
• tester.pump(): Re-renders the frame (synchronous setState).
• tester.pumpAndSettle(): Repeatedly pumps until there are no more scheduled frames or animations.
• find.byKey(Key('myKey')): Most stable selector for testing.
• find.byType(ElevatedButton): Selects by widget type.

---

2. Unit Testing Business Logic & State

Test ViewModels, Repositories, or Bloc without UI:

import 'package:test/test.dart';
import 'package:mocktail/mocktail.dart';
import 'package:myapp/data/repositories/auth_repository.dart';
import 'package:myapp/ui/auth_viewmodel.dart';

class MockAuthRepository extends Mock implements AuthRepository {}

void main() {
  late MockAuthRepository mockRepo;
  late AuthViewModel viewModel;

  setUp(() {
    mockRepo = MockAuthRepository();
    viewModel = AuthViewModel(repository: mockRepo);
  });

  test('login success updates state to authenticated', () async {
    when(() => mockRepo.login('[email protected]', 'secret'))
        .thenAnswer((_) async => const User(id: '123', email: '[email protected]'));

    await viewModel.login('[email protected]', 'secret');

    expect(viewModel.isAuthenticated, isTrue);
    expect(viewModel.currentUser?.id, equals('123'));
  });
}