flutter-testing

Overview

Per flutter-testing-doc:

"Flutter uses a testing pyramid approach with three main categories":

1. Unit Tests - single function / method / class; mocked dependencies; quick.
2. Widget Tests - single widget; UI + lifecycle + interactions; quick.
3. Integration Tests - full app or large sections; on real devices/emulators; highest confidence; slowest.

The framework ships first-party tooling for all three layers.

When to use

• The app is Flutter (the framework's intended use case).
• The team uses Dart and wants test-stack consistency with production code.

Step 1 - Install

Flutter ships with flutter_test (in the SDK). For mocks:

# pubspec.yaml
dev_dependencies:
  flutter_test:
    sdk: flutter
  integration_test:
    sdk: flutter
  mockito: ^5.4.4
  build_runner: ^2.4.13

Step 2 - Unit tests

Pure-Dart functions with mocked dependencies:

// test/cart_test.dart
import 'package:flutter_test/flutter_test.dart';
import 'package:my_app/cart.dart';

void main() {
  group('Cart', () {
    test('addItem increments count', () {
      final cart = Cart();
      cart.addItem(Item(sku: 'BOOK-001', qty: 1));
      expect(cart.itemCount, 1);
    });

    test('addItem rejects negative qty', () {
      final cart = Cart();
      expect(
        () => cart.addItem(Item(sku: 'BOOK-001', qty: -1)),
        throwsA(isA<ArgumentError>()),
      );
    });
  });
}

Run:

flutter test test/cart_test.dart
flutter test                       # all tests
flutter test --coverage            # produces coverage/lcov.info

The LCOV output feeds lcov-analysis (in the qa-test-reporting plugin).

Step 3 - Widget tests

Per flutter-testing-doc, widget tests "verify the UI looks and interacts as expected":

// test/cart_screen_test.dart
import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';
import 'package:my_app/cart_screen.dart';

void main() {
  testWidgets('CartScreen shows item count', (WidgetTester tester) async {
    await tester.pumpWidget(MaterialApp(home: CartScreen(initialCount: 3)));

    expect(find.text('3 items'), findsOneWidget);
    expect(find.byKey(Key('add-to-cart-button')), findsOneWidget);
  });

  testWidgets('Tapping add button increments count', (WidgetTester tester) async {
    await tester.pumpWidget(MaterialApp(home: CartScreen(initialCount: 0)));

    await tester.tap(find.byKey(Key('add-to-cart-button')));
    await tester.pump();   // rebuild after state change

    expect(find.text('1 item'), findsOneWidget);
  });
}

tester.pumpWidget(...) mounts the widget tree. tester.pump() advances the frame; tester.pumpAndSettle() advances until no animations are pending.

Finders:

Finder	Use
find.byKey(Key(...))	By Key (preferred for stable lookups).
find.text("...")	By visible text (translation-fragile).
find.byType(Widget)	By widget type.
find.byIcon(Icons.x)	By Material icon.
find.descendant(of:, matching:)	Nested matching.

Step 4 - Integration tests

Per flutter-testing-doc, integration tests "test complete app or large app sections" on real devices.

// integration_test/checkout_flow_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('checkout flow', (WidgetTester tester) async {
    app.main();
    await tester.pumpAndSettle();

    await tester.tap(find.byKey(Key('login-button')));
    await tester.pumpAndSettle();

    await tester.enterText(find.byKey(Key('email-field')), 'qa-test@example.com');
    // ... etc.
  });
}

Run:

# On a connected device or simulator/emulator
flutter test integration_test/checkout_flow_test.dart

Step 5 - Mockito + build_runner

For mocks:

// test/cart_test.dart
import 'package:mockito/annotations.dart';
import 'package:mockito/mockito.dart';
import 'cart_test.mocks.dart';   // generated

@GenerateMocks([CartRepo])
void main() {
  test('Cart loads from repo', () async {
    final mockRepo = MockCartRepo();
    when(mockRepo.getCart()).thenAnswer(
      (_) async => Cart(items: [Item(sku: 'BOOK-001', qty: 1)]),
    );

    final cart = await mockRepo.getCart();
    expect(cart.itemCount, 1);
    verify(mockRepo.getCart()).called(1);
  });
}

Generate the *.mocks.dart files:

dart run build_runner build --delete-conflicting-outputs

Step 6 - Coverage + reporting

flutter test --coverage           # writes coverage/lcov.info
genhtml coverage/lcov.info -o coverage/html   # human report

The LCOV file feeds the same parser other plugins use (lcov-analysis) for cross-language coverage aggregation.

Step 7 - CI integration

jobs:
  test:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v5
      - uses: subosito/flutter-action@v2
        with:
          channel: stable
      - run: flutter pub get
      - run: dart run build_runner build --delete-conflicting-outputs
      - run: flutter test --coverage
      - uses: codecov/codecov-action@v5
        with:
          files: coverage/lcov.info

  integration-android:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v5
      - uses: subosito/flutter-action@v2
      - uses: reactivecircus/android-emulator-runner@v2
        with:
          api-level: 34
          script: flutter test integration_test/

Per flutter-testing-doc, Flutter supports CI integration via "Fastlane / Travis CI / Cirrus CI / Codemagic / Bitrise / Appcircle / Patrol (for native platform interactions)."

Anti-patterns

Anti-pattern	Why it fails	Fix
All tests as integration tests	Slow; fragile; hides per-layer issues per the pyramid.	Many unit + widget; few integration (Step 1 pyramid).
find.text("...") for translatable strings	Translation breaks tests.	find.byKey(Key("...")) (Step 3).
tester.pump() (single frame) for animations	Animation isn't done; assertion fires too early.	tester.pumpAndSettle() for animations.
Skipping IntegrationTestWidgetsFlutterBinding.ensureInitialized()	Integration test won't bind; runtime errors.	Add as first line in main() (Step 4).
Mock without @GenerateMocks (manual mock classes)	Tedious; drift when the SUT interface changes.	Use @GenerateMocks + build_runner (Step 5).
Coverage from integration tests only	Integration coverage is sparse; misses unit-level branches.	Coverage from flutter test (which runs unit + widget).

Limitations

• flutter drive deprecated for new projects. Use integration_test package (modern; Step 4).
• Native platform features need extra packages. For things like permissions / camera / push notifications, use patrol or per-platform native integration.
• Widget tests use a fake Stub for MediaQuery etc. Surface varies vs production; widget tests don't cover layout/font issues that need a real renderer.
• Mockito's null safety story. Generation handles it; manual mocks are awkward.

References

• ft - Flutter testing pyramid: unit / widget / integration; trade-off matrix (confidence, maintenance, deps, speed); CI integration list; flutter test / flutter drive commands.
• xcuitest-suite, espresso-suite, detox-testing - alternative framework wrappers when the app isn't Flutter.
• lcov-analysis - downstream consumer of flutter test --coverage.