flutter-testing-skill

name	flutter-testing-skill
description	Generates Flutter widget tests, integration tests, and golden tests in Dart. Supports local execution and TestMu AI cloud for real device testing. Use when user mentions "Flutter", "widget test", "WidgetTester", "testWidgets", "flutter_test", "integration_test". Triggers on: "Flutter", "widget test", "Dart test", "testWidgets", "WidgetTester", "golden test".
languages	["Dart"]
category	mobile-testing
license	MIT
metadata	{"author":"TestMu AI","version":"1.0"}

Flutter Testing Skill

You are a senior Flutter developer specializing in testing.

Step 1 — Test Type

├─ "unit test", "business logic", "model test"
│  └─ Unit test: test/ directory, flutter_test package
│
├─ "widget test", "component test", "UI test"
│  └─ Widget test: test/ directory, testWidgets()
│
├─ "integration test", "E2E", "full app test"
│  └─ Integration test: integration_test/ directory
│
├─ "golden test", "snapshot", "visual regression"
│  └─ Golden test: matchesGoldenFile()
│
└─ Ambiguous? → Widget test (most common)

Core Patterns — Dart

Widget Test (Most Common)

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:my_app/screens/login_screen.dart';

void main() {
  testWidgets('Login screen shows email and password fields', (WidgetTester tester) async {
    await tester.pumpWidget(const MaterialApp(home: LoginScreen()));

    // Verify fields exist
    expect(find.byType(TextField), findsNWidgets(2));
    expect(find.text('Email'), findsOneWidget);
    expect(find.text('Password'), findsOneWidget);
    expect(find.byType(ElevatedButton), findsOneWidget);
  });

  testWidgets('Login with valid credentials navigates to dashboard', (WidgetTester tester) async {
    await tester.pumpWidget(const MaterialApp(home: LoginScreen()));

    // Enter credentials
    await tester.enterText(find.byKey(const Key('emailField')), '[e-mail]');
    await tester.enterText(find.byKey(const Key('passwordField')), 'password123');

    // Tap login button
    await tester.tap(find.byKey(const Key('loginButton')));
    await tester.pumpAndSettle(); // Wait for animations and navigation

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

  testWidgets('Shows error for invalid credentials', (WidgetTester tester) async {
    await tester.pumpWidget(const MaterialApp(home: LoginScreen()));

    await tester.enterText(find.byKey(const Key('emailField')), '[e-mail]');
    await tester.enterText(find.byKey(const Key('passwordField')), 'wrong');
    await tester.tap(find.byKey(const Key('loginButton')));
    await tester.pumpAndSettle();

    expect(find.text('Invalid credentials'), findsOneWidget);
  });
}

Finder Strategies

// By Key (best — explicit test identifiers)
find.byKey(const Key('loginButton'))
find.byKey(const ValueKey('email_input'))

// By Type
find.byType(ElevatedButton)
find.byType(TextField)
find.byType(LoginScreen)

// By Text
find.text('Login')
find.textContaining('Welcome')

// By Icon
find.byIcon(Icons.login)

// By Widget predicate
find.byWidgetPredicate((widget) => widget is Text && widget.data!.startsWith('Error'))

// Descendant/Ancestor
find.descendant(of: find.byType(AppBar), matching: find.text('Title'))
find.ancestor(of: find.text('Login'), matching: find.byType(Card))

Actions

await tester.tap(finder);                    // Tap
await tester.longPress(finder);              // Long press
await tester.enterText(finder, 'text');      // Type text
await tester.drag(finder, const Offset(0, -300));  // Drag/scroll
await tester.fling(finder, const Offset(0, -500), 1000); // Fling/swipe

// CRITICAL: Always pump after actions
await tester.pump();                         // Single frame
await tester.pump(const Duration(seconds: 1)); // Advance time
await tester.pumpAndSettle();                // Wait for animations to finish

Integration Test

// integration_test/app_test.dart
import 'package:flutter_test/flutter_test.dart';
import 'package:integration_test/integration_test.dart';
import 'package:my_app/main.dart' as app;

void main() {
  IntegrationTestWidgetsFlutterBinding.ensureInitialized();

  testWidgets('Full login flow', (WidgetTester tester) async {
    app.main();
    await tester.pumpAndSettle();

    // Login
    await tester.enterText(find.byKey(const Key('emailField')), '[e-mail]');
    await tester.enterText(find.byKey(const Key('passwordField')), 'password123');
    await tester.tap(find.byKey(const Key('loginButton')));
    await tester.pumpAndSettle();

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

    // Navigate to settings
    await tester.tap(find.byIcon(Icons.settings));
    await tester.pumpAndSettle();
    expect(find.text('Settings'), findsOneWidget);
  });
}

Golden Tests (Visual Regression)

testWidgets('Login screen matches golden', (WidgetTester tester) async {
  await tester.pumpWidget(const MaterialApp(home: LoginScreen()));
  await tester.pumpAndSettle();

  await expectLater(
    find.byType(LoginScreen),
    matchesGoldenFile('goldens/login_screen.png'),
  );
});

# Generate golden files
flutter test --update-goldens

# Run golden comparison
flutter test

Mocking Dependencies

// Using Mockito
import 'package:mockito/mockito.dart';
import 'package:mockito/annotations.dart';

@GenerateMocks([AuthService])
void main() {
  late MockAuthService mockAuth;

  setUp(() {
    mockAuth = MockAuthService();
  });

  testWidgets('Login calls auth service', (tester) async {
    when(mockAuth.login(any, any)).thenAnswer((_) async => true);

    await tester.pumpWidget(MaterialApp(
      home: LoginScreen(authService: mockAuth),
    ));

    await tester.enterText(find.byKey(const Key('emailField')), '[e-mail]');
    await tester.enterText(find.byKey(const Key('passwordField')), 'pass123');
    await tester.tap(find.byKey(const Key('loginButton')));
    await tester.pumpAndSettle();

    verify(mockAuth.login('[e-mail]', 'pass123')).called(1);
  });
}

Anti-Patterns

Bad	Good	Why
No pumpAndSettle() after action	Always pump after interactions	Animations not complete
find.text() for dynamic text	find.byKey()	Locale/text changes break tests
Testing implementation details	Test user-facing behavior	Brittle
No mocking in widget tests	Mock services, repos	Tests hit real APIs

TestMu AI Cloud (Integration Tests)

# Run integration tests on LambdaTest real devices
# 1. Build app for testing
flutter build apk --debug  # Android
flutter build ios --simulator  # iOS

# 2. Upload to LambdaTest
curl -u "$LT_USERNAME:$LT_ACCESS_KEY" \
  -X POST "https://manual-api.lambdatest.com/app/upload/realDevice" \
  -F "appFile=@build/app/outputs/flutter-apk/app-debug.apk"

# 3. Run via Appium (Flutter driver)
# Use appium-flutter-driver for element interaction

Quick Reference

Task	Command
Run all tests	flutter test
Run specific file	flutter test test/login_test.dart
Run with coverage	flutter test --coverage
Run integration tests	flutter test integration_test/
Update goldens	flutter test --update-goldens
Generate mocks	flutter pub run build_runner build
Test specific platform	flutter test --platform chrome

pubspec.yaml

dev_dependencies:
  flutter_test:
    sdk: flutter
  integration_test:
    sdk: flutter
  mockito: ^5.4.0
  build_runner: ^2.4.0

Deep Patterns

For advanced patterns, debugging guides, CI/CD integration, and best practices, see reference/playbook.md.