Add integration test for taking screenshots of the example

Ref: #315

.github/workflows/flutter-ci.yml

@@ -58,6 +58,28 @@ jobs:
     - name: Check for any formatting issues
       run: dart format --set-exit-if-changed .
 
+  integration:
+    runs-on: ubuntu-20.04
+    steps:
+
+    - uses: actions/checkout@v2
+    - uses: subosito/flutter-action@v2
+      with:
+        channel: 'stable'
+        flutter-version: '3.10.x'
+
+    - name: Install dependencies
+      run: |
+        sudo apt update
+        sudo apt -y install clang cmake curl libgtk-3-dev ninja-build pkg-config unzip xvfb
+
+    - name: Get dependencies
+      run: flutter pub get
+
+    - name: Run integration tests
+      run: xvfb-run -a -s '-screen 0 1280x800x24 +extension GLX' flutter test -d linux integration_test
+      working-directory: example/
+
   pub:
     runs-on: ubuntu-20.04
     steps:

example/integration_test/screenshot_test.dart

@@ -0,0 +1,116 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:integration_test/integration_test.dart';
+import 'package:yaru/yaru.dart';
+import 'package:yaru_example/main.dart' as app;
+import 'package:yaru_example/main.dart';
+import 'package:yaru_example/view/home_page.dart';
+
+// NOTE: run `flutter test --update-goldens integration_test` to update screenshots
+
+Future<void> main() async {
+  IntegrationTestWidgetsFlutterBinding.ensureInitialized();
+
+  testWidgets('fonts', (tester) async {
+    tester.runApp();
+    await tester.pumpAndSettle();
+    await tester.takeScreenshots('fonts');
+  });
+
+  testWidgets('buttons', (tester) async {
+    tester.runApp();
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Controls'));
+    await tester.pump();
+    await tester.takeScreenshots('buttons');
+  });
+
+  testWidgets('checks', (tester) async {
+    tester.runApp();
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Controls'));
+    await tester.pump();
+    await tester.tap(find.text('Checks'));
+    await tester.pump();
+    await tester.takeScreenshots('checks');
+  });
+
+  testWidgets('switches', (tester) async {
+    tester.runApp();
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Controls'));
+    await tester.pump();
+    await tester.tap(find.text('Switches'));
+    await tester.pump();
+    await tester.takeScreenshots('switches');
+  });
+
+  testWidgets('text fields', (tester) async {
+    tester.runApp();
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Text Fields'));
+    await tester.pump();
+    primaryFocus?.unfocus();
+    await tester.pump();
+    await tester.takeScreenshots('text-fields');
+  });
+
+  testWidgets('containers', (tester) async {
+    tester.runApp();
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Containers'));
+    await tester.pump();
+    await tester.takeScreenshots('containers');
+  });
+}
+
+extension on WidgetTester {
+  void runApp() {
+    view.physicalSize = const Size(600, 700);
+    app.main();
+  }
+
+  void selectTheme({
+    YaruVariant? variant,
+    bool? highContrast,
+    ThemeMode? themeMode,
+  }) async {
+    final context = element(find.byType(HomePage));
+    AppTheme.apply(
+      context,
+      variant: variant,
+      highContrast: highContrast,
+      themeMode: themeMode,
+    );
+  }
+
+  Future<void> takeScreenshots(String screen) async {
+    for (final themeMode in [ThemeMode.light, ThemeMode.dark]) {
+      selectTheme(
+        variant: YaruVariant.orange,
+        themeMode: themeMode,
+        highContrast: false,
+      );
+      await pumpAndSettle();
+      await takeScreenshot(screen);
+
+      selectTheme(themeMode: themeMode, highContrast: true);
+      await pumpAndSettle();
+      await takeScreenshot(screen);
+    }
+  }
+
+  Future<void> takeScreenshot(String screen) async {
+    final context = element(find.byType(HomePage));
+    final theme = AppTheme.of(context);
+    final suffix = [
+      if (theme.highContrast == true) 'high-contrast' else theme.variant?.name,
+      theme.themeMode?.name,
+    ].join('-');
+
+    await expectLater(
+      find.byType(MaterialApp),
+      matchesGoldenFile('screenshots/$screen-$suffix.png'),
+    );
+  }
+}

example/pubspec.yaml

@@ -18,6 +18,8 @@ dev_dependencies:
   flutter_lints: ^2.0.1
   flutter_test:
     sdk: flutter
+  integration_test:
+    sdk: flutter
 
 flutter:
   uses-material-design: true