Add integration test for taking screenshots of the example

Ref: #315

example/integration_test/screenshot_test.dart

@@ -0,0 +1,133 @@
+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/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 {
+    app.main();
+    await tester.pumpAndSettle();
+    await tester.takeScreenshots('fonts');
+  });
+
+  testWidgets('buttons', (tester) async {
+    app.main();
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Controls'));
+    await tester.pump();
+    await tester.takeScreenshots('buttons');
+  });
+
+  testWidgets('checks', (tester) async {
+    app.main();
+    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 {
+    app.main();
+    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 {
+    app.main();
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Text Fields'));
+    await tester.pump();
+    await tester.takeScreenshots('switches');
+  });
+
+  testWidgets('containers', (tester) async {
+    app.main();
+    await tester.pumpAndSettle();
+    await tester.tap(find.text('Containers'));
+    await tester.pump();
+    await tester.takeScreenshots('containers');
+  });
+}
+
+extension on WidgetTester {
+  Brightness get brightness {
+    final context = element(find.byType(HomePage));
+    return Theme.of(context).brightness;
+  }
+
+  YaruVariant get variant {
+    final context = element(find.byType(HomePage));
+    return YaruTheme.of(context).variant!;
+  }
+
+  bool get highContrast {
+    final context = element(find.byType(HomePage));
+    return YaruTheme.of(context).highContrast!;
+  }
+
+  Future<void> toggleBrightness() async {
+    for (final icon in [Icons.light_mode, Icons.dark_mode]) {
+      final button = find.widgetWithIcon(TextButton, icon);
+      if (button.evaluate().isNotEmpty) {
+        await tap(button);
+        await pumpAndSettle();
+        break;
+      }
+    }
+  }
+
+  Future<void> selectTheme(Color color) async {
+    await tap(find.byType(PopupMenuButton<Color>));
+    await pumpAndSettle();
+
+    final menuItem = find.byWidgetPredicate((widget) {
+      return widget is PopupMenuItem<Color> && widget.value == color;
+    });
+    await ensureVisible(menuItem);
+    await tap(menuItem);
+    await pumpAndSettle();
+  }
+
+  Future<void> takeScreenshots(String screen) async {
+    for (var i = 0; i < 2; ++i) {
+      await toggleBrightness();
+
+      await selectTheme(YaruVariant.orange.color);
+      await takeScreenshot(screen);
+
+      switch (brightness) {
+        case Brightness.light:
+          await selectTheme(Colors.black);
+          break;
+        case Brightness.dark:
+          await selectTheme(Colors.white);
+          break;
+      }
+      await takeScreenshot(screen);
+    }
+  }
+
+  Future<void> takeScreenshot(String screen) async {
+    final suffix = [
+      if (highContrast) 'high-contrast' else variant.name,
+      brightness.name,
+    ].join('-');
+
+    await expectLater(
+      find.byType(MaterialApp),
+      matchesGoldenFile('screenshots/$screen-$suffix.png'),
+    );
+  }
+}

example/lib/view/home_page.dart

@@ -69,6 +69,9 @@ class HomePageState extends State<HomePage> {
             itemBuilder: (context) {
               return [
                 PopupMenuItem(
+                  value: theme.themeMode == ThemeMode.light
+                      ? Colors.black
+                      : Colors.white,
                   onTap: () => AppTheme.apply(context, highContrast: true),
                   child: Row(
                     children: [
@@ -84,6 +87,7 @@ class HomePageState extends State<HomePage> {
                 ),
                 for (final variant in YaruVariant.values) // skip flavors
                   PopupMenuItem(
+                    value: variant.color,
                     onTap: () => AppTheme.apply(
                       context,
                       variant: variant,

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