Add golden test

Ref: #315

.github/workflows/flutter-ci.yml

@@ -58,6 +58,35 @@ jobs:
     - name: Check for any formatting issues
       run: dart format --set-exit-if-changed .
 
+  goldens:
+    runs-on: ubuntu-22.04
+    steps:
+
+    - uses: actions/checkout@v2
+    - uses: subosito/flutter-action@v2
+      with:
+        channel: 'stable'
+        flutter-version: '3.10.x'
+
+    - name: Install apt dependencies
+      run: |
+        sudo apt update
+        sudo apt -y install clang cmake curl libgtk-3-dev ninja-build pkg-config unzip xvfb
+        sudo apt -y install fonts-noto-cjk fonts-ubuntu fonts-tibetan-machine
+
+    - name: Get pub dependencies
+      run: flutter pub get
+
+    - name: Run golden tests
+      run: xvfb-run -a -s '-screen 0 1280x800x24 +extension GLX' flutter test integration_test/golden_test.dart -d linux
+      working-directory: example/
+
+    - uses: actions/upload-artifact@v3
+      if: failure()
+      with:
+        name: failures
+        path: example/integration_test/failures
+
   pub:
     runs-on: ubuntu-20.04
     steps:

Makefile

@@ -0,0 +1,3 @@
+.PHONY: goldens
+goldens:
+	cd example && GDK_BACKEND=x11 GDK_SCALE=1 flutter test integration_test/golden_test.dart -d linux --update-goldens

example/integration_test/golden_test.dart

@@ -0,0 +1,158 @@
+import 'dart:typed_data';
+
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:integration_test/integration_test.dart';
+import 'package:path/path.dart' as path;
+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 `make goldens` to update golden images
+
+const _kGoldenDiffTolerance = 0.005;
+
+Future<void> main() async {
+  IntegrationTestWidgetsFlutterBinding.ensureInitialized();
+
+  goldenFileComparator = GoldenDiffComparator(
+    path.join(
+      path.fromUri((goldenFileComparator as LocalFileComparator).basedir),
+      'yaru.dart',
+    ),
+    tolerance: _kGoldenDiffTolerance,
+  );
+
+  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.devicePixelRatio = 1;
+    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('goldens/$screen-$suffix.png'),
+    );
+  }
+}
+
+class GoldenDiffComparator extends LocalFileComparator {
+  GoldenDiffComparator(
+    String testFile, {
+    required this.tolerance,
+  }) : super(Uri.parse(testFile));
+
+  final double tolerance;
+
+  @override
+  Future<bool> compare(Uint8List imageBytes, Uri golden) async {
+    final ComparisonResult result = await GoldenFileComparator.compareLists(
+      imageBytes,
+      await getGoldenBytes(golden),
+    );
+
+    if (!result.passed && result.diffPercent > tolerance) {
+      final error = await generateFailureOutput(result, golden, basedir);
+      throw FlutterError(error);
+    }
+    if (!result.passed) {
+      debugPrint(
+        'A tolerable difference of ${result.diffPercent * 100}% was found when comparing $golden.',
+      );
+    }
+    return result.passed || result.diffPercent <= tolerance;
+  }
+}

example/pubspec.yaml

@@ -18,6 +18,9 @@ dev_dependencies:
   flutter_lints: ^2.0.1
   flutter_test:
     sdk: flutter
+  integration_test:
+    sdk: flutter
+  path: ^1.8.3
 
 flutter:
   uses-material-design: true