[Material 3] Add optional indicator to Navigation Rail. (#92930)

packages/flutter/lib/src/material/navigation_bar.dart

@@ -300,7 +300,7 @@ class NavigationDestination extends StatelessWidget {
         return Stack(
           alignment: Alignment.center,
           children: <Widget>[
-            _NavigationIndicator(
+            NavigationIndicator(
               animation: animation,
               color: navigationBarTheme.indicatorColor,
             ),
@@ -507,20 +507,24 @@ class _NavigationDestinationInfo extends InheritedWidget {
   }
 }
 
-/// Selection Indicator for the Material 3 Navigation Bar component.
+/// Selection Indicator for the Material 3 [NavigationBar] and [NavigationRail]
+/// components.
 ///
 /// When [animation] is 0, the indicator is not present. As [animation] grows
 /// from 0 to 1, the indicator scales in on the x axis.
 ///
-/// Useful in a [Stack] widget behind the icons in the Material 3 Navigation Bar
+/// Used in a [Stack] widget behind the icons in the Material 3 Navigation Bar
 /// to illuminate the selected destination.
-class _NavigationIndicator extends StatelessWidget {
+class NavigationIndicator extends StatelessWidget {
   /// Builds an indicator, usually used in a stack behind the icon of a
   /// navigation bar destination.
-  const _NavigationIndicator({
+  const NavigationIndicator({
     Key? key,
     required this.animation,
     this.color,
+    this.width = 64,
+    this.height = 32,
+    this.borderRadius = const BorderRadius.all(Radius.circular(16)),
   }) : super(key: key);
 
   /// Determines the scale of the indicator.
@@ -534,6 +538,21 @@ class _NavigationIndicator extends StatelessWidget {
   /// If null, defaults to [ColorScheme.secondary].
   final Color? color;
 
+  /// The width of the container that holds in the indicator.
+  ///
+  /// Defaults to `64`.
+  final double width;
+
+  /// The height of the container that holds in the indicator.
+  ///
+  /// Defaults to `32`.
+  final double height;
+
+  /// The radius of the container that holds in the indicator.
+  ///
+  /// Defaults to `BorderRadius.circular(16)`.
+  final BorderRadius borderRadius;
+
   @override
   Widget build(BuildContext context) {
     final ColorScheme colorScheme = Theme.of(context).colorScheme;
@@ -573,10 +592,10 @@ class _NavigationIndicator extends StatelessWidget {
               return FadeTransition(
                 opacity: fadeAnimation,
                 child: Container(
-                  width: 64.0,
-                  height: 32.0,
+                  width: width,
+                  height: height,
                   decoration: BoxDecoration(
-                    borderRadius: const BorderRadius.all(Radius.circular(16.0)),
+                    borderRadius: borderRadius,
                     color: color ?? colorScheme.secondary.withOpacity(.24),
                   ),
                 ),

packages/flutter/lib/src/material/navigation_rail.dart

@@ -10,6 +10,7 @@ import 'color_scheme.dart';
 import 'ink_well.dart';
 import 'material.dart';
 import 'material_localizations.dart';
+import 'navigation_bar.dart';
 import 'navigation_rail_theme.dart';
 import 'theme.dart';
 
@@ -94,6 +95,8 @@ class NavigationRail extends StatefulWidget {
     this.selectedIconTheme,
     this.minWidth,
     this.minExtendedWidth,
+    this.useIndicator,
+    this.indicatorColor,
   }) :  assert(destinations != null && destinations.length >= 2),
         assert(selectedIndex != null),
         assert(0 <= selectedIndex && selectedIndex < destinations.length),
@@ -279,6 +282,21 @@ class NavigationRail extends StatefulWidget {
   /// The default value is 256.
   final double? minExtendedWidth;
 
+  /// If `true`, adds a rounded [NavigationIndicator] behind the selected
+  /// destination's icon.
+  ///
+  /// The indicator's shape will be circular if [labelType] is
+  /// [NavigationRailLabelType.none], or a [StadiumBorder] if [labelType] is
+  /// [NavigationRailLabelType.all] or [NavigationRailLabelType.selected].
+  ///
+  /// If `null`, defaults to [NavigationRailThemeData.useIndicator]. If that is
+  /// `null`, defaults to [ThemeData.useMaterial3].
+  final bool? useIndicator;
+
+  /// Overrides the default value of [NavigationRail]'s selection indicator color,
+  /// when [useIndicator] is true.
+  final Color? indicatorColor;
+
   /// Returns the animation that controls the [NavigationRail.extended] state.
   ///
   /// This can be used to synchronize animations in the [leading] or [trailing]
@@ -413,6 +431,8 @@ class _NavigationRailState extends State<NavigationRail> with TickerProviderStat
                           iconTheme: widget.selectedIndex == i ? selectedIconTheme : unselectedIconTheme,
                           labelTextStyle: widget.selectedIndex == i ? selectedLabelTextStyle : unselectedLabelTextStyle,
                           padding: widget.destinations[i].padding,
+                          useIndicator: widget.useIndicator ?? navigationRailTheme.useIndicator ?? theme.useMaterial3,
+                          indicatorColor: widget.indicatorColor ?? navigationRailTheme.indicatorColor,
                           onTap: () {
                             if (widget.onDestinationSelected != null)
                               widget.onDestinationSelected!(i);
@@ -498,6 +518,8 @@ class _RailDestination extends StatelessWidget {
     required this.onTap,
     required this.indexLabel,
     this.padding,
+    required this.useIndicator,
+    this.indicatorColor,
   }) : assert(minWidth != null),
        assert(minExtendedWidth != null),
        assert(icon != null),
@@ -529,11 +551,18 @@ class _RailDestination extends StatelessWidget {
   final VoidCallback onTap;
   final String indexLabel;
   final EdgeInsetsGeometry? padding;
+  final bool useIndicator;
+  final Color? indicatorColor;
 
   final Animation<double> _positionAnimation;
 
   @override
   Widget build(BuildContext context) {
+    assert(
+      useIndicator || indicatorColor == null,
+      '[NavigationRail.indicatorColor] does not have an effect when [NavigationRail.useIndicator] is false',
+    );
+
     final Widget themedIcon = IconTheme(
       data: iconTheme,
       child: icon,
@@ -542,13 +571,19 @@ class _RailDestination extends StatelessWidget {
       style: labelTextStyle,
       child: label,
     );
+
     final Widget content;
+
     switch (labelType) {
       case NavigationRailLabelType.none:
         final Widget iconPart = SizedBox(
           width: minWidth,
           height: minWidth,
-          child: Align(
+          child: _AddIndicator(
+            addIndicator: useIndicator,
+            indicatorColor: indicatorColor,
+            isCircular: true,
+            indicatorAnimation: destinationAnimation,
             child: themedIcon,
           ),
         );
@@ -606,6 +641,7 @@ class _RailDestination extends StatelessWidget {
         final double verticalPadding = lerpDouble(_verticalDestinationPaddingNoLabel, _verticalDestinationPaddingWithLabel, appearingAnimationValue)!;
         final Interval interval = selected ? const Interval(0.25, 0.75) : const Interval(0.75, 1.0);
         final Animation<double> labelFadeAnimation = destinationAnimation.drive(CurveTween(curve: interval));
+
         content = Container(
           constraints: BoxConstraints(
             minWidth: minWidth,
@@ -618,7 +654,13 @@ class _RailDestination extends StatelessWidget {
               mainAxisAlignment: MainAxisAlignment.center,
               children: <Widget>[
                 SizedBox(height: verticalPadding),
-                themedIcon,
+                _AddIndicator(
+                  addIndicator: useIndicator,
+                  indicatorColor: indicatorColor,
+                  isCircular: false,
+                  indicatorAnimation: destinationAnimation,
+                  child: themedIcon,
+                ),
                 Align(
                   alignment: Alignment.topCenter,
                   heightFactor: appearingAnimationValue,
@@ -645,7 +687,13 @@ class _RailDestination extends StatelessWidget {
           child: Column(
             children: <Widget>[
               const SizedBox(height: _verticalDestinationPaddingWithLabel),
-              themedIcon,
+              _AddIndicator(
+                addIndicator: useIndicator,
+                indicatorColor: indicatorColor,
+                isCircular: false,
+                indicatorAnimation: destinationAnimation,
+                child: themedIcon,
+              ),
               styledLabel,
               const SizedBox(height: _verticalDestinationPaddingWithLabel),
             ],
@@ -682,6 +730,62 @@ class _RailDestination extends StatelessWidget {
   }
 }
 
+/// When [addIndicator] is `true`, puts [child] center aligned in a [Stack] with
+/// a [NavigationIndicator] behind it, otherwise returns [child].
+///
+/// When [isCircular] is true, the indicator will be a circle, otherwise the
+/// indicator will be a stadium shape.
+class _AddIndicator extends StatelessWidget {
+  const _AddIndicator({
+    Key? key,
+    required this.addIndicator,
+    required this.isCircular,
+    required this.indicatorColor,
+    required this.indicatorAnimation,
+    required this.child,
+  }) : super(key: key);
+
+  final bool addIndicator;
+  final bool isCircular;
+  final Color? indicatorColor;
+  final Animation<double> indicatorAnimation;
+  final Widget child;
+
+  @override
+  Widget build(BuildContext context) {
+    if (!addIndicator) {
+      return child;
+    }
+    late final Widget indicator;
+    if (isCircular) {
+      const double circularIndicatorDiameter = 56;
+      indicator = NavigationIndicator(
+        animation: indicatorAnimation,
+        height: circularIndicatorDiameter,
+        width: circularIndicatorDiameter,
+        borderRadius: BorderRadius.circular(circularIndicatorDiameter / 2),
+        color: indicatorColor,
+      );
+    } else {
+      indicator = NavigationIndicator(
+        animation: indicatorAnimation,
+        width: 56,
+        borderRadius: BorderRadius.circular(16),
+        color: indicatorColor,
+      );
+    }
+
+    return Stack(
+      alignment: Alignment.center,
+      children: <Widget>[
+        indicator,
+        child,
+      ],
+    );
+  }
+}
+
+
 /// Defines the behavior of the labels of a [NavigationRail].
 ///
 /// See also:

packages/flutter/lib/src/material/navigation_rail_theme.dart

@@ -44,6 +44,8 @@ class NavigationRailThemeData with Diagnosticable {
     this.selectedIconTheme,
     this.groupAlignment,
     this.labelType,
+    this.useIndicator,
+    this.indicatorColor,
   });
 
   /// Color to be used for the [NavigationRail]'s background.
@@ -76,6 +78,14 @@ class NavigationRailThemeData with Diagnosticable {
   /// [NavigationRail].
   final NavigationRailLabelType? labelType;
 
+  /// Whether or not the selected [NavigationRailDestination] should include a
+  /// [NavigationIndicator].
+  final bool? useIndicator;
+
+  /// Overrides the default value of [NavigationRail]'s selection indicator color,
+  /// when [useIndicator] is true.
+  final Color? indicatorColor;
+
   /// Creates a copy of this object with the given fields replaced with the
   /// new values.
   NavigationRailThemeData copyWith({
@@ -87,6 +97,8 @@ class NavigationRailThemeData with Diagnosticable {
     IconThemeData? selectedIconTheme,
     double? groupAlignment,
     NavigationRailLabelType? labelType,
+    bool? useIndicator,
+    Color? indicatorColor,
   }) {
     return NavigationRailThemeData(
       backgroundColor: backgroundColor ?? this.backgroundColor,
@@ -97,6 +109,8 @@ class NavigationRailThemeData with Diagnosticable {
       selectedIconTheme: selectedIconTheme ?? this.selectedIconTheme,
       groupAlignment: groupAlignment ?? this.groupAlignment,
       labelType: labelType ?? this.labelType,
+      useIndicator: useIndicator ?? this.useIndicator,
+      indicatorColor: indicatorColor ?? this.indicatorColor,
     );
   }
 
@@ -118,6 +132,8 @@ class NavigationRailThemeData with Diagnosticable {
       selectedIconTheme: IconThemeData.lerp(a?.selectedIconTheme, b?.selectedIconTheme, t),
       groupAlignment: lerpDouble(a?.groupAlignment, b?.groupAlignment, t),
       labelType: t < 0.5 ? a?.labelType : b?.labelType,
+      useIndicator: t < 0.5 ? a?.useIndicator : b?.useIndicator,
+      indicatorColor: Color.lerp(a?.indicatorColor, b?.indicatorColor, t),
     );
   }
 
@@ -132,6 +148,8 @@ class NavigationRailThemeData with Diagnosticable {
       selectedIconTheme,
       groupAlignment,
       labelType,
+      useIndicator,
+      indicatorColor,
     );
   }
 
@@ -149,7 +167,9 @@ class NavigationRailThemeData with Diagnosticable {
         && other.unselectedIconTheme == unselectedIconTheme
         && other.selectedIconTheme == selectedIconTheme
         && other.groupAlignment == groupAlignment
-        && other.labelType == labelType;
+        && other.labelType == labelType
+        && other.useIndicator == useIndicator
+        && other.indicatorColor == indicatorColor;
   }
 
   @override
@@ -165,6 +185,8 @@ class NavigationRailThemeData with Diagnosticable {
     properties.add(DiagnosticsProperty<IconThemeData>('selectedIconTheme', selectedIconTheme, defaultValue: defaultData.selectedIconTheme));
     properties.add(DoubleProperty('groupAlignment', groupAlignment, defaultValue: defaultData.groupAlignment));
     properties.add(DiagnosticsProperty<NavigationRailLabelType>('labelType', labelType, defaultValue: defaultData.labelType));
+    properties.add(DiagnosticsProperty<bool>('useIndicator', useIndicator, defaultValue: defaultData.useIndicator));
+    properties.add(ColorProperty('indicatorColor', indicatorColor, defaultValue: defaultData.indicatorColor));
   }
 }
 

packages/flutter/test/material/navigation_rail_test.dart

@@ -2160,6 +2160,195 @@ void main() {
     expect(secondItem.padding, secondItemPadding);
     expect(thirdItem.padding, thirdItemPadding);
   });
+
+  testWidgets('NavigationRailDestination adds indicator by default when ThemeData.useMaterial3 is true', (WidgetTester tester) async {
+    await _pumpNavigationRail(
+      tester,
+      theme: ThemeData(useMaterial3: true),
+      navigationRail: NavigationRail(
+        labelType: NavigationRailLabelType.selected,
+        selectedIndex: 0,
+        destinations: const <NavigationRailDestination>[
+          NavigationRailDestination(
+            icon: Icon(Icons.favorite_border),
+            selectedIcon: Icon(Icons.favorite),
+            label: Text('Abc'),
+          ),
+          NavigationRailDestination(
+            icon: Icon(Icons.bookmark_border),
+            selectedIcon: Icon(Icons.bookmark),
+            label: Text('Def'),
+          ),
+          NavigationRailDestination(
+            icon: Icon(Icons.star_border),
+            selectedIcon: Icon(Icons.star),
+            label: Text('Ghi'),
+          ),
+        ],
+      ),
+    );
+
+    expect(find.byType(NavigationIndicator), findsWidgets);
+  });
+
+  testWidgets('NavigationRailDestination adds indicator when useIndicator is true', (WidgetTester tester) async {
+    await _pumpNavigationRail(
+      tester,
+      navigationRail: NavigationRail(
+        useIndicator: true,
+        labelType: NavigationRailLabelType.selected,
+        selectedIndex: 0,
+        destinations: const <NavigationRailDestination>[
+          NavigationRailDestination(
+            icon: Icon(Icons.favorite_border),
+            selectedIcon: Icon(Icons.favorite),
+            label: Text('Abc'),
+          ),
+          NavigationRailDestination(
+            icon: Icon(Icons.bookmark_border),
+            selectedIcon: Icon(Icons.bookmark),
+            label: Text('Def'),
+          ),
+          NavigationRailDestination(
+            icon: Icon(Icons.star_border),
+            selectedIcon: Icon(Icons.star),
+            label: Text('Ghi'),
+          ),
+        ],
+      ),
+    );
+
+    expect(find.byType(NavigationIndicator), findsWidgets);
+  });
+
+  testWidgets('NavigationRailDestination does not add indicator when useIndicator is false', (WidgetTester tester) async {
+    await _pumpNavigationRail(
+      tester,
+      navigationRail: NavigationRail(
+        useIndicator: false,
+        labelType: NavigationRailLabelType.selected,
+        selectedIndex: 0,
+        destinations: const <NavigationRailDestination>[
+          NavigationRailDestination(
+            icon: Icon(Icons.favorite_border),
+            selectedIcon: Icon(Icons.favorite),
+            label: Text('Abc'),
+          ),
+          NavigationRailDestination(
+            icon: Icon(Icons.bookmark_border),
+            selectedIcon: Icon(Icons.bookmark),
+            label: Text('Def'),
+          ),
+          NavigationRailDestination(
+            icon: Icon(Icons.star_border),
+            selectedIcon: Icon(Icons.star),
+            label: Text('Ghi'),
+          ),
+        ],
+      ),
+    );
+
+    expect(find.byType(NavigationIndicator), findsNothing);
+  });
+
+  testWidgets('NavigationRailDestination adds circular indicator when no labels are present', (WidgetTester tester) async {
+    await _pumpNavigationRail(
+      tester,
+      navigationRail: NavigationRail(
+        useIndicator: true,
+        labelType: NavigationRailLabelType.none,
+        selectedIndex: 0,
+        destinations: const <NavigationRailDestination>[
+          NavigationRailDestination(
+            icon: Icon(Icons.favorite_border),
+            selectedIcon: Icon(Icons.favorite),
+            label: Text('Abc'),
+          ),
+          NavigationRailDestination(
+            icon: Icon(Icons.bookmark_border),
+            selectedIcon: Icon(Icons.bookmark),
+            label: Text('Def'),
+          ),
+          NavigationRailDestination(
+            icon: Icon(Icons.star_border),
+            selectedIcon: Icon(Icons.star),
+            label: Text('Ghi'),
+          ),
+        ],
+      ),
+    );
+
+    final NavigationIndicator indicator = tester.widget<NavigationIndicator>(find.byType(NavigationIndicator).first);
+
+    expect(indicator.width, 56);
+    expect(indicator.height, 56);
+  });
+
+  testWidgets('NavigationRailDestination adds circular indicator when selected labels are present', (WidgetTester tester) async {
+    await _pumpNavigationRail(
+      tester,
+      navigationRail: NavigationRail(
+        useIndicator: true,
+        labelType: NavigationRailLabelType.selected,
+        selectedIndex: 0,
+        destinations: const <NavigationRailDestination>[
+          NavigationRailDestination(
+            icon: Icon(Icons.favorite_border),
+            selectedIcon: Icon(Icons.favorite),
+            label: Text('Abc'),
+          ),
+          NavigationRailDestination(
+            icon: Icon(Icons.bookmark_border),
+            selectedIcon: Icon(Icons.bookmark),
+            label: Text('Def'),
+          ),
+          NavigationRailDestination(
+            icon: Icon(Icons.star_border),
+            selectedIcon: Icon(Icons.star),
+            label: Text('Ghi'),
+          ),
+        ],
+      ),
+    );
+
+    final NavigationIndicator indicator = tester.widget<NavigationIndicator>(find.byType(NavigationIndicator).first);
+
+    expect(indicator.width, 56);
+    expect(indicator.height, 32);
+  });
+
+  testWidgets('NavigationRailDestination adds circular indicator when all labels are present', (WidgetTester tester) async {
+    await _pumpNavigationRail(
+      tester,
+      navigationRail: NavigationRail(
+        useIndicator: true,
+        labelType: NavigationRailLabelType.all,
+        selectedIndex: 0,
+        destinations: const <NavigationRailDestination>[
+          NavigationRailDestination(
+            icon: Icon(Icons.favorite_border),
+            selectedIcon: Icon(Icons.favorite),
+            label: Text('Abc'),
+          ),
+          NavigationRailDestination(
+            icon: Icon(Icons.bookmark_border),
+            selectedIcon: Icon(Icons.bookmark),
+            label: Text('Def'),
+          ),
+          NavigationRailDestination(
+            icon: Icon(Icons.star_border),
+            selectedIcon: Icon(Icons.star),
+            label: Text('Ghi'),
+          ),
+        ],
+      ),
+    );
+
+    final NavigationIndicator indicator = tester.widget<NavigationIndicator>(find.byType(NavigationIndicator).first);
+
+    expect(indicator.width, 56);
+    expect(indicator.height, 32);
+  });
 }
 
 TestSemantics _expectedSemantics() {
@@ -2243,9 +2432,11 @@ Future<void> _pumpNavigationRail(
   WidgetTester tester, {
   double textScaleFactor = 1.0,
   required NavigationRail navigationRail,
+  ThemeData? theme,
 }) async {
   await tester.pumpWidget(
     MaterialApp(
+      theme: theme,
       home: Builder(
         builder: (BuildContext context) {
           return MediaQuery(

packages/flutter/test/material/navigation_rail_theme_test.dart

@@ -36,6 +36,7 @@ void main() {
     expect(_unselectedLabelStyle(tester).fontSize, 14.0);
     expect(_destinationsAlign(tester).alignment, Alignment.topCenter);
     expect(_labelType(tester), NavigationRailLabelType.none);
+    expect(find.byType(NavigationIndicator), findsNothing);
   });
 
   testWidgets('NavigationRailThemeData values are used when no NavigationRail properties are specified', (WidgetTester tester) async {
@@ -51,6 +52,8 @@ void main() {
     const double unselectedLabelFontSize = 11.0;
     const double groupAlignment = 0.0;
     const NavigationRailLabelType labelType = NavigationRailLabelType.all;
+    const bool useIndicator = true;
+    const Color indicatorColor = Color(0x00000004);
 
     await tester.pumpWidget(
       MaterialApp(
@@ -73,6 +76,8 @@ void main() {
               unselectedLabelTextStyle: TextStyle(fontSize: unselectedLabelFontSize),
               groupAlignment: groupAlignment,
               labelType: labelType,
+              useIndicator: useIndicator,
+              indicatorColor: indicatorColor,
             ),
             child: NavigationRail(
               selectedIndex: 0,
@@ -95,6 +100,8 @@ void main() {
     expect(_unselectedLabelStyle(tester).fontSize, unselectedLabelFontSize);
     expect(_destinationsAlign(tester).alignment, Alignment.center);
     expect(_labelType(tester), labelType);
+    expect(find.byType(NavigationIndicator), findsWidgets);
+    expect(_indicatorDecoration(tester)?.color, indicatorColor);
   });
 
   testWidgets('NavigationRail values take priority over NavigationRailThemeData values when both properties are specified', (WidgetTester tester) async {
@@ -110,6 +117,8 @@ void main() {
     const double unselectedLabelFontSize = 11.0;
     const double groupAlignment = 0.0;
     const NavigationRailLabelType labelType = NavigationRailLabelType.all;
+    const bool useIndicator = true;
+    const Color indicatorColor = Color(0x00000004);
 
     await tester.pumpWidget(
       MaterialApp(
@@ -132,6 +141,8 @@ void main() {
               unselectedLabelTextStyle: TextStyle(fontSize: 7.0),
               groupAlignment: 1.0,
               labelType: NavigationRailLabelType.selected,
+              useIndicator: false,
+              indicatorColor: Color(0x00000096),
             ),
             child: NavigationRail(
               selectedIndex: 0,
@@ -152,6 +163,8 @@ void main() {
               unselectedLabelTextStyle: const TextStyle(fontSize: unselectedLabelFontSize),
               groupAlignment: groupAlignment,
               labelType: labelType,
+              useIndicator: useIndicator,
+              indicatorColor: indicatorColor,
             ),
           ),
         ),
@@ -170,6 +183,8 @@ void main() {
     expect(_unselectedLabelStyle(tester).fontSize, unselectedLabelFontSize);
     expect(_destinationsAlign(tester).alignment, Alignment.center);
     expect(_labelType(tester), labelType);
+    expect(find.byType(NavigationIndicator), findsWidgets);
+    expect(_indicatorDecoration(tester)?.color, indicatorColor);
   });
 
   testWidgets('Default debugFillProperties', (WidgetTester tester) async {
@@ -195,6 +210,8 @@ void main() {
       unselectedLabelTextStyle: TextStyle(fontSize: 7.0),
       groupAlignment: 1.0,
       labelType: NavigationRailLabelType.selected,
+      useIndicator: true,
+      indicatorColor: Color(0x00000096),
     ).debugFillProperties(builder);
 
     final List<String> description = builder.properties
@@ -215,7 +232,8 @@ void main() {
 
     expect(description[6], 'groupAlignment: 1.0');
     expect(description[7], 'labelType: NavigationRailLabelType.selected');
-
+    expect(description[8], 'useIndicator: true');
+    expect(description[9], 'indicatorColor: Color(0x00000096)');
   });
 }
 
@@ -244,6 +262,16 @@ Material _railMaterial(WidgetTester tester) {
   );
 }
 
+
+BoxDecoration? _indicatorDecoration(WidgetTester tester) {
+  return tester.firstWidget<Container>(
+    find.descendant(
+      of: find.byType(NavigationIndicator),
+      matching: find.byType(Container),
+    ),
+  ).decoration as BoxDecoration?;
+}
+
 IconThemeData _selectedIconTheme(WidgetTester tester) {
   return _iconTheme(tester, Icons.favorite);
 }