feat(flutter): 统一空列表占位组件

test/empty_state/empty_state_test.dart

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+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'package:fruitshorts/core/theme/app_colors.dart';
+import 'package:fruitshorts/core/theme/app_theme.dart';
+import 'package:fruitshorts/core/widgets/empty_state.dart';
+
+void main() {
+  testWidgets('should_render_title_subtitle_action_and_title_only_semantics', (
+    tester,
+  ) async {
+    var taps = 0;
+    await _pump(
+      tester,
+      theme: AppTheme.dark(),
+      child: EmptyState(
+        icon: Icons.movie_outlined,
+        title: 'No stories',
+        subtitle: 'New content will appear here.',
+        actionLabel: 'Retry',
+        onAction: () => taps++,
+      ),
+    );
+
+    expect(find.byKey(const Key('empty-state-art')), findsOneWidget);
+    expect(find.byKey(const Key('empty-state-icon')), findsOneWidget);
+    expect(find.text('No stories'), findsOneWidget);
+    expect(find.text('New content will appear here.'), findsOneWidget);
+    expect(
+      tester.getSize(find.byKey(const Key('empty-state-art'))),
+      const Size(96, 96),
+    );
+    expect(
+      tester.getSize(find.byKey(const Key('empty-state-icon'))),
+      const Size(42, 42),
+    );
+    expect(
+      tester
+          .widget<Text>(find.byKey(const Key('empty-state-title')))
+          .style
+          ?.fontSize,
+      16,
+    );
+    expect(
+      tester.getSize(find.byKey(const Key('empty-state-action'))).height,
+      greaterThanOrEqualTo(44),
+    );
+
+    final semantics = tester.ensureSemantics();
+    expect(find.bySemanticsLabel('No stories'), findsOneWidget);
+    expect(
+      find.bySemanticsLabel('New content will appear here.'),
+      findsNothing,
+    );
+
+    await tester.tap(find.byKey(const Key('empty-state-action')));
+    expect(taps, 1);
+    semantics.dispose();
+  });
+
+  testWidgets('should_render_compact_dimensions_for_embedded_empty_state', (
+    tester,
+  ) async {
+    await _pump(
+      tester,
+      child: const EmptyState(
+        icon: Icons.chat_bubble_outline_rounded,
+        title: 'No comments yet.',
+        compact: true,
+      ),
+    );
+
+    expect(
+      tester.getSize(find.byKey(const Key('empty-state-art'))),
+      const Size(64, 64),
+    );
+    expect(
+      tester.getSize(find.byKey(const Key('empty-state-icon'))),
+      const Size(28, 28),
+    );
+    expect(
+      tester
+          .widget<Text>(find.byKey(const Key('empty-state-title')))
+          .style
+          ?.fontSize,
+      14,
+    );
+    expect(find.byKey(const Key('empty-state-action')), findsNothing);
+  });
+
+  testWidgets('should_use_theme_aware_icon_colors', (tester) async {
+    await _pump(
+      tester,
+      theme: AppTheme.dark(),
+      child: const EmptyState(icon: Icons.history_rounded, title: 'No history'),
+    );
+    expect(
+      tester.widget<Icon>(find.byKey(const Key('empty-state-icon'))).color,
+      AppColors.blueSoft,
+    );
+
+    await _pump(
+      tester,
+      theme: AppTheme.light(),
+      child: const EmptyState(icon: Icons.history_rounded, title: 'No history'),
+    );
+    expect(
+      tester.widget<Icon>(find.byKey(const Key('empty-state-icon'))).color,
+      AppColors.blue,
+    );
+  });
+
+  testWidgets('should_fit_compact_width_without_overflow', (tester) async {
+    tester.view.physicalSize = const Size(320, 568);
+    tester.view.devicePixelRatio = 1;
+    addTearDown(tester.view.resetPhysicalSize);
+    addTearDown(tester.view.resetDevicePixelRatio);
+
+    await _pump(
+      tester,
+      child: const EmptyState(
+        icon: Icons.download_outlined,
+        title: 'No download authorizations yet.',
+        subtitle: 'New content will appear here.',
+        actionLabel: 'Retry',
+      ),
+    );
+
+    final content = tester.widget<ConstrainedBox>(
+      find.byKey(const Key('empty-state-content')),
+    );
+    expect(content.constraints.maxWidth, 280);
+    expect(tester.takeException(), isNull);
+  });
+}
+
+Future<void> _pump(
+  WidgetTester tester, {
+  ThemeData? theme,
+  required Widget child,
+}) async {
+  await tester.pumpWidget(
+    MaterialApp(
+      theme: theme ?? AppTheme.dark(),
+      home: Scaffold(body: child),
+    ),
+  );
+  await tester.pumpAndSettle();
+}