Add `AnimationStyle` to `ExpansionTile` (#139664)

fixes [Expose animation parameters for the [ExpansionTile] widget](https://github.com/flutter/flutter/issues/138047)

### Description
Add `AnimationStyle` to the `ExpansionTile` widget to override the default expand and close animation.

Syntax:
```dart
        child: ExpansionTile(
          title: const Text('Tap to expand'),
          expansionAnimationStyle: AnimationStyle(
            duration: Durations.extralong1,
            curve: Easing.emphasizedAccelerate,
          ),
          children: const <Widget>[FlutterLogo(size: 200)],
        ),
```

### Code sample

<details>
<summary>expand to view the code sample</summary> 

```dart
// Copyright 2014 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/material.dart';

/// Flutter code sample for [ExpansionTile] and [AnimationStyle].

void main() {
  runApp(const ExpansionTileAnimationStyleApp());
}

enum AnimationStyles { defaultStyle, custom, none }
const List<(AnimationStyles, String)> animationStyleSegments = <(AnimationStyles, String)>[
  (AnimationStyles.defaultStyle, 'Default'),
  (AnimationStyles.custom, 'Custom'),
  (AnimationStyles.none, 'None'),
];

class ExpansionTileAnimationStyleApp extends StatefulWidget {
  const ExpansionTileAnimationStyleApp({super.key});

  @override
  State<ExpansionTileAnimationStyleApp> createState() => _ExpansionTileAnimationStyleAppState();
}

class _ExpansionTileAnimationStyleAppState extends State<ExpansionTileAnimationStyleApp> {
  Set<AnimationStyles> _animationStyleSelection = <AnimationStyles>{AnimationStyles.defaultStyle};
  AnimationStyle? _animationStyle;

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: SafeArea(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
              SegmentedButton<AnimationStyles>(
                selected: _animationStyleSelection,
                onSelectionChanged: (Set<AnimationStyles> styles) {
                  setState(() {
                    _animationStyleSelection = styles;
                    switch (styles.first) {
                      case AnimationStyles.defaultStyle:
                        _animationStyle = null;
                      case AnimationStyles.custom:
                        _animationStyle = AnimationStyle(
                          curve: Easing.emphasizedAccelerate,
                          duration: Durations.extralong1,
                        );
                      case AnimationStyles.none:
                        _animationStyle = AnimationStyle.noAnimation;
                    }
                  });
                },
                segments: animationStyleSegments
                  .map<ButtonSegment<AnimationStyles>>(((AnimationStyles, String) shirt) {
                    return ButtonSegment<AnimationStyles>(value: shirt.$1, label: Text(shirt.$2));
                  })
                  .toList(),
              ),
              const SizedBox(height: 20),
              ExpansionTile(
                expansionAnimationStyle: _animationStyle,
                title: const Text('ExpansionTile'),
                children: const <Widget>[
                  ListTile(title: Text('Expanded Item 1')),
                  ListTile(title: Text('Expanded Item 2')),
                ],
              )
            ],
          ),
        ),
      ),
    );
  }
}
```

</details>

Related to https://github.com/flutter/flutter/pull/138721.

examples/api/lib/material/expansion_tile/expansion_tile.2.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+
+/// Flutter code sample for [ExpansionTile] and [AnimationStyle].
+
+void main() {
+  runApp(const ExpansionTileAnimationStyleApp());
+}
+
+enum AnimationStyles { defaultStyle, custom, none }
+const List<(AnimationStyles, String)> animationStyleSegments = <(AnimationStyles, String)>[
+  (AnimationStyles.defaultStyle, 'Default'),
+  (AnimationStyles.custom, 'Custom'),
+  (AnimationStyles.none, 'None'),
+];
+
+class ExpansionTileAnimationStyleApp extends StatefulWidget {
+  const ExpansionTileAnimationStyleApp({super.key});
+
+  @override
+  State<ExpansionTileAnimationStyleApp> createState() => _ExpansionTileAnimationStyleAppState();
+}
+
+class _ExpansionTileAnimationStyleAppState extends State<ExpansionTileAnimationStyleApp> {
+  Set<AnimationStyles> _animationStyleSelection = <AnimationStyles>{AnimationStyles.defaultStyle};
+  AnimationStyle? _animationStyle;
+
+  @override
+  Widget build(BuildContext context) {
+    return MaterialApp(
+      home: Scaffold(
+        body: SafeArea(
+          child: Column(
+            mainAxisAlignment: MainAxisAlignment.center,
+            children: <Widget>[
+              SegmentedButton<AnimationStyles>(
+                selected: _animationStyleSelection,
+                onSelectionChanged: (Set<AnimationStyles> styles) {
+                  setState(() {
+                    _animationStyleSelection = styles;
+                    switch (styles.first) {
+                      case AnimationStyles.defaultStyle:
+                        _animationStyle = null;
+                      case AnimationStyles.custom:
+                        _animationStyle = AnimationStyle(
+                          curve: Easing.emphasizedAccelerate,
+                          duration: Durations.extralong1,
+                        );
+                      case AnimationStyles.none:
+                        _animationStyle = AnimationStyle.noAnimation;
+                    }
+                  });
+                },
+                segments: animationStyleSegments
+                  .map<ButtonSegment<AnimationStyles>>(((AnimationStyles, String) shirt) {
+                    return ButtonSegment<AnimationStyles>(value: shirt.$1, label: Text(shirt.$2));
+                  })
+                  .toList(),
+              ),
+              const SizedBox(height: 20),
+              ExpansionTile(
+                expansionAnimationStyle: _animationStyle,
+                title: const Text('ExpansionTile'),
+                children: const <Widget>[
+                  ListTile(title: Text('Expanded Item 1')),
+                  ListTile(title: Text('Expanded Item 2')),
+                ],
+              )
+            ],
+          ),
+        ),
+      ),
+    );
+  }
+}

examples/api/test/material/expansion_tile/expansion_tile.2_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/material.dart';
+import 'package:flutter_api_samples/material/expansion_tile/expansion_tile.2.dart' as example;
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  testWidgets('ExpansionTile animation can be customized using AnimationStyle', (WidgetTester tester) async {
+    await tester.pumpWidget(
+      const example.ExpansionTileAnimationStyleApp(),
+    );
+
+    double getHeight(WidgetTester tester) {
+      return tester.getSize(find.byType(ExpansionTile)).height;
+    }
+
+    expect(getHeight(tester), 58.0);
+
+    // Test the default animation style.
+    await tester.tap(find.text('ExpansionTile'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 100));
+
+    expect(getHeight(tester), closeTo(93.4, 0.1));
+
+    await tester.pumpAndSettle();
+
+    expect(getHeight(tester), 170.0);
+
+    // Tap to collapse.
+    await tester.tap(find.text('ExpansionTile'));
+    await tester.pumpAndSettle();
+
+    // Test the custom animation style.
+    await tester.tap(find.text('Custom'));
+    await tester.pumpAndSettle();
+
+    await tester.tap(find.text('ExpansionTile'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 100));
+
+    expect(getHeight(tester), closeTo(59.2, 0.1));
+
+    await tester.pumpAndSettle();
+
+    expect(getHeight(tester), 170.0);
+
+    // Tap to collapse.
+    await tester.tap(find.text('ExpansionTile'));
+    await tester.pumpAndSettle();
+
+    // Test the no animation style.
+    await tester.tap(find.text('None'));
+    await tester.pumpAndSettle();
+
+    await tester.tap(find.text('ExpansionTile'));
+    await tester.pump();
+
+    expect(getHeight(tester), 170.0);
+  });
+}

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

@@ -252,6 +252,7 @@ class ExpansionTile extends StatefulWidget {
     this.dense,
     this.visualDensity,
     this.enableFeedback = true,
+    this.expansionAnimationStyle,
   }) : assert(
        expandedCrossAxisAlignment != CrossAxisAlignment.baseline,
        'CrossAxisAlignment.baseline is not supported since the expanded children '
@@ -506,6 +507,28 @@ class ExpansionTile extends StatefulWidget {
   /// {@macro flutter.material.ListTile.enableFeedback}
   final bool? enableFeedback;
 
+  /// Used to override the expansion animation curve and duration.
+  ///
+  /// If [AnimationStyle.duration] is provided, it will be used to override
+  /// the expansion animation duration. If it is null, then [AnimationStyle.duration]
+  /// from the [ExpansionTileThemeData.expansionAnimationStyle] will be used.
+  /// Otherwise, defaults to 200ms.
+  ///
+  /// If [AnimationStyle.curve] is provided, it will be used to override
+  /// the expansion animation curve. If it is null, then [AnimationStyle.curve]
+  /// from the [ExpansionTileThemeData.expansionAnimationStyle] will be used.
+  /// Otherwise, defaults to [Curves.easeIn].
+  ///
+  /// To disable the theme animation, use [AnimationStyle.noAnimation].
+  ///
+  /// {@tool dartpad}
+  /// This sample showcases how to override the [ExpansionTile] expansion
+  /// animation curve and duration using [AnimationStyle].
+  ///
+  /// ** See code in examples/api/lib/material/expansion_tile/expansion_tile.2.dart **
+  /// {@end-tool}
+  final AnimationStyle? expansionAnimationStyle;
+
   @override
   State<ExpansionTile> createState() => _ExpansionTileState();
 }
@@ -519,6 +542,7 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
   final ColorTween _headerColorTween = ColorTween();
   final ColorTween _iconColorTween = ColorTween();
   final ColorTween _backgroundColorTween = ColorTween();
+  final CurveTween _heightFactorTween = CurveTween(curve: Curves.easeIn);
 
   late AnimationController _animationController;
   late Animation<double> _iconTurns;
@@ -535,7 +559,7 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
   void initState() {
     super.initState();
     _animationController = AnimationController(duration: _kExpand, vsync: this);
-    _heightFactor = _animationController.drive(_easeInTween);
+    _heightFactor = _animationController.drive(_heightFactorTween);
     _iconTurns = _animationController.drive(_halfTween.chain(_easeInTween));
     _border = _animationController.drive(_borderTween.chain(_easeOutTween));
     _headerColor = _animationController.drive(_headerColorTween.chain(_easeInTween));
@@ -711,6 +735,10 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
       || widget.collapsedBackgroundColor != oldWidget.collapsedBackgroundColor) {
       _updateBackgroundColor(expansionTileTheme);
     }
+    if (widget.expansionAnimationStyle != oldWidget.expansionAnimationStyle) {
+      _updateAnimationDuration(expansionTileTheme);
+      _updateHeightFactorCurve(expansionTileTheme);
+    }
   }
 
   @override
@@ -720,13 +748,21 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
     final ExpansionTileThemeData defaults = theme.useMaterial3
       ? _ExpansionTileDefaultsM3(context)
       : _ExpansionTileDefaultsM2(context);
+    _updateAnimationDuration(expansionTileTheme);
     _updateShapeBorder(expansionTileTheme, theme);
     _updateHeaderColor(expansionTileTheme, defaults);
     _updateIconColor(expansionTileTheme, defaults);
     _updateBackgroundColor(expansionTileTheme);
+    _updateHeightFactorCurve(expansionTileTheme);
     super.didChangeDependencies();
   }
 
+  void _updateAnimationDuration(ExpansionTileThemeData expansionTileTheme) {
+    _animationController.duration = widget.expansionAnimationStyle?.duration
+      ?? expansionTileTheme.expansionAnimationStyle?.duration
+      ?? _kExpand;
+  }
+
   void _updateShapeBorder(ExpansionTileThemeData expansionTileTheme, ThemeData theme) {
     _borderTween
       ..begin = widget.collapsedShape
@@ -765,6 +801,12 @@ class _ExpansionTileState extends State<ExpansionTile> with SingleTickerProvider
       ..end = widget.backgroundColor ?? expansionTileTheme.backgroundColor;
   }
 
+  void _updateHeightFactorCurve(ExpansionTileThemeData expansionTileTheme) {
+    _heightFactorTween.curve = widget.expansionAnimationStyle?.curve
+      ?? expansionTileTheme.expansionAnimationStyle?.curve
+      ?? Curves.easeIn;
+  }
+
   @override
   Widget build(BuildContext context) {
     final ExpansionTileThemeData expansionTileTheme = ExpansionTileTheme.of(context);

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

@@ -52,6 +52,7 @@ class ExpansionTileThemeData with Diagnosticable {
     this.shape,
     this.collapsedShape,
     this.clipBehavior,
+    this.expansionAnimationStyle,
   });
 
   /// Overrides the default value of [ExpansionTile.backgroundColor].
@@ -90,6 +91,9 @@ class ExpansionTileThemeData with Diagnosticable {
   /// Overrides the default value of [ExpansionTile.clipBehavior].
   final Clip? clipBehavior;
 
+  /// Overrides the default value of [ExpansionTile.expansionAnimationStyle].
+  final AnimationStyle? expansionAnimationStyle;
+
   /// Creates a copy of this object with the given fields replaced with the
   /// new values.
   ExpansionTileThemeData copyWith({
@@ -105,6 +109,7 @@ class ExpansionTileThemeData with Diagnosticable {
     ShapeBorder? shape,
     ShapeBorder? collapsedShape,
     Clip? clipBehavior,
+    AnimationStyle? expansionAnimationStyle,
   }) {
     return ExpansionTileThemeData(
       backgroundColor: backgroundColor ?? this.backgroundColor,
@@ -119,6 +124,7 @@ class ExpansionTileThemeData with Diagnosticable {
       shape: shape ?? this.shape,
       collapsedShape: collapsedShape ?? this.collapsedShape,
       clipBehavior: clipBehavior ?? this.clipBehavior,
+      expansionAnimationStyle: expansionAnimationStyle ?? this.expansionAnimationStyle,
     );
   }
 
@@ -139,6 +145,8 @@ class ExpansionTileThemeData with Diagnosticable {
       collapsedTextColor: Color.lerp(a?.collapsedTextColor, b?.collapsedTextColor, t),
       shape: ShapeBorder.lerp(a?.shape, b?.shape, t),
       collapsedShape: ShapeBorder.lerp(a?.collapsedShape, b?.collapsedShape, t),
+      clipBehavior: t < 0.5 ? a?.clipBehavior : b?.clipBehavior,
+      expansionAnimationStyle: t < 0.5 ? a?.expansionAnimationStyle : b?.expansionAnimationStyle,
     );
   }
 
@@ -157,6 +165,7 @@ class ExpansionTileThemeData with Diagnosticable {
       shape,
       collapsedShape,
       clipBehavior,
+      expansionAnimationStyle,
     );
   }
 
@@ -180,7 +189,8 @@ class ExpansionTileThemeData with Diagnosticable {
       && other.collapsedTextColor == collapsedTextColor
       && other.shape == shape
       && other.collapsedShape == collapsedShape
-      && other.clipBehavior == clipBehavior;
+      && other.clipBehavior == clipBehavior
+      && other.expansionAnimationStyle == expansionAnimationStyle;
   }
 
   @override
@@ -198,6 +208,7 @@ class ExpansionTileThemeData with Diagnosticable {
     properties.add(DiagnosticsProperty<ShapeBorder>('shape', shape, defaultValue: null));
     properties.add(DiagnosticsProperty<ShapeBorder>('collapsedShape', collapsedShape, defaultValue: null));
     properties.add(DiagnosticsProperty<Clip>('clipBehavior', clipBehavior, defaultValue: null));
+    properties.add(DiagnosticsProperty<AnimationStyle>('expansionAnimationStyle', expansionAnimationStyle, defaultValue: null));
   }
 }
 

packages/flutter/test/material/expansion_tile_test.dart

@@ -1049,6 +1049,107 @@ void main() {
     expect(tester.state<TestTextState>(find.byType(TestText)).textStyle.color, const Color(0xffffffff));
   });
 
+  testWidgetsWithLeakTracking('Override ExpansionTile animation using AnimationStyle', (WidgetTester tester) async {
+    const Key expansionTileKey = Key('expansionTileKey');
+
+    Widget buildExpansionTile({ AnimationStyle? animationStyle }) {
+      return MaterialApp(
+        home: Material(
+          child: Center(
+            child: ExpansionTile(
+              key: expansionTileKey,
+              expansionAnimationStyle: animationStyle,
+              title: const TestText('title'),
+              children: const <Widget>[
+                SizedBox(height: 100, width: 100),
+              ],
+            ),
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildExpansionTile());
+
+    double getHeight(Key key) => tester.getSize(find.byKey(key)).height;
+
+    // Test initial ExpansionTile height.
+    expect(getHeight(expansionTileKey), 58.0);
+
+    // Test the default expansion animation.
+    await tester.tap(find.text('title'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 50)); // Advance the animation by 1/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(67.4, 0.1));
+
+    await tester.pump(const Duration(milliseconds: 50)); // Advance the animation by 2/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(89.6, 0.1));
+
+    await tester.pumpAndSettle(); // Advance the animation to the end.
+
+    expect(getHeight(expansionTileKey), 158.0);
+
+    // Tap to collapse the ExpansionTile.
+    await tester.tap(find.text('title'));
+    await tester.pumpAndSettle();
+
+    // Override the animation duration.
+    await tester.pumpWidget(buildExpansionTile(animationStyle: AnimationStyle(duration: const Duration(milliseconds: 800))));
+    await tester.pumpAndSettle();
+
+    // Test the overridden animation duration.
+    await tester.tap(find.text('title'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 200)); // Advance the animation by 1/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(67.4, 0.1));
+
+    await tester.pump(const Duration(milliseconds: 200)); // Advance the animation by 2/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(89.6, 0.1));
+
+    await tester.pumpAndSettle(); // Advance the animation to the end.
+
+    expect(getHeight(expansionTileKey), 158.0);
+
+    // Tap to collapse the ExpansionTile.
+    await tester.tap(find.text('title'));
+    await tester.pumpAndSettle();
+
+    // Override the animation curve.
+    await tester.pumpWidget(buildExpansionTile(animationStyle: AnimationStyle(curve: Easing.emphasizedDecelerate)));
+    await tester.pumpAndSettle();
+
+    // Test the overridden animation curve.
+    await tester.tap(find.text('title'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 50)); // Advance the animation by 1/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(141.2, 0.1));
+
+    await tester.pump(const Duration(milliseconds: 50)); // Advance the animation by 2/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(153, 0.1));
+
+    await tester.pumpAndSettle(); // Advance the animation to the end.
+
+    expect(getHeight(expansionTileKey), 158.0);
+
+    // Tap to collapse the ExpansionTile.
+    await tester.tap(find.text('title'));
+
+    // Test no animation.
+    await tester.pumpWidget(buildExpansionTile(animationStyle: AnimationStyle.noAnimation));
+
+    // Tap to expand the ExpansionTile.
+    await tester.tap(find.text('title'));
+    await tester.pump();
+
+    expect(getHeight(expansionTileKey), 158.0);
+  });
+
   group('Material 2', () {
     // These tests are only relevant for Material 2. Once Material 2
     // support is deprecated and the APIs are removed, these tests

packages/flutter/test/material/expansion_tile_theme_test.dart

@@ -68,6 +68,7 @@ void main() {
     expect(theme.shape, null);
     expect(theme.collapsedShape, null);
     expect(theme.clipBehavior, null);
+    expect(theme.expansionAnimationStyle, null);
   });
 
   testWidgetsWithLeakTracking('Default ExpansionTileThemeData debugFillProperties', (WidgetTester tester) async {
@@ -84,19 +85,20 @@ void main() {
 
   testWidgetsWithLeakTracking('ExpansionTileThemeData implements debugFillProperties', (WidgetTester tester) async {
     final DiagnosticPropertiesBuilder builder = DiagnosticPropertiesBuilder();
-    const ExpansionTileThemeData(
-      backgroundColor: Color(0xff000000),
-      collapsedBackgroundColor: Color(0xff6f83fc),
-      tilePadding: EdgeInsets.all(20.0),
+    ExpansionTileThemeData(
+      backgroundColor: const Color(0xff000000),
+      collapsedBackgroundColor: const Color(0xff6f83fc),
+      tilePadding: const EdgeInsets.all(20.0),
       expandedAlignment: Alignment.bottomCenter,
-      childrenPadding: EdgeInsets.all(10.0),
-      iconColor: Color(0xffa7c61c),
-      collapsedIconColor: Color(0xffdd0b1f),
-      textColor: Color(0xffffffff),
-      collapsedTextColor: Color(0xff522bab),
-      shape: Border(),
-      collapsedShape: Border(),
+      childrenPadding: const EdgeInsets.all(10.0),
+      iconColor: const Color(0xffa7c61c),
+      collapsedIconColor: const Color(0xffdd0b1f),
+      textColor: const Color(0xffffffff),
+      collapsedTextColor: const Color(0xff522bab),
+      shape: const Border(),
+      collapsedShape: const Border(),
       clipBehavior: Clip.antiAlias,
+      expansionAnimationStyle: AnimationStyle(curve: Curves.easeInOut),
     ).debugFillProperties(builder);
 
     final List<String> description = builder.properties
@@ -104,7 +106,7 @@ void main() {
         .map((DiagnosticsNode node) => node.toString())
         .toList();
 
-    expect(description, <String>[
+    expect(description, equalsIgnoringHashCodes(<String>[
       'backgroundColor: Color(0xff000000)',
       'collapsedBackgroundColor: Color(0xff6f83fc)',
       'tilePadding: EdgeInsets.all(20.0)',
@@ -117,7 +119,8 @@ void main() {
       'shape: Border.all(BorderSide(width: 0.0, style: none))',
       'collapsedShape: Border.all(BorderSide(width: 0.0, style: none))',
       'clipBehavior: Clip.antiAlias',
-    ]);
+      'expansionAnimationStyle: AnimationStyle#983ac(curve: Cubic(0.42, 0.00, 0.58, 1.00))',
+    ]));
   });
 
   testWidgetsWithLeakTracking('ExpansionTileTheme - collapsed', (WidgetTester tester) async {
@@ -305,4 +308,109 @@ void main() {
     expect(childRect.right, paddingRect.right - 20);
     expect(childRect.bottom, paddingRect.bottom - 20);
   });
+
+  testWidgetsWithLeakTracking('Override ExpansionTile animation using ExpansionTileThemeData.AnimationStyle', (WidgetTester tester) async {
+    const Key expansionTileKey = Key('expansionTileKey');
+
+    Widget buildExpansionTile({ AnimationStyle? animationStyle }) {
+      return MaterialApp(
+        theme: ThemeData(
+          expansionTileTheme: ExpansionTileThemeData(
+            expansionAnimationStyle: animationStyle,
+          ),
+        ),
+        home: const Material(
+          child: Center(
+            child: ExpansionTile(
+              key: expansionTileKey,
+              title: TestText('title'),
+              children: <Widget>[
+                SizedBox(height: 100, width: 100),
+              ],
+            ),
+          ),
+        ),
+      );
+    }
+
+    await tester.pumpWidget(buildExpansionTile());
+
+    double getHeight(Key key) => tester.getSize(find.byKey(key)).height;
+
+    // Test initial ExpansionTile height.
+    expect(getHeight(expansionTileKey), 58.0);
+
+    // Test the default expansion animation.
+    await tester.tap(find.text('title'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 50)); // Advance the animation by 1/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(67.4, 0.1));
+
+    await tester.pump(const Duration(milliseconds: 50)); // Advance the animation by 2/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(89.6, 0.1));
+
+    await tester.pumpAndSettle(); // Advance the animation to the end.
+
+    expect(getHeight(expansionTileKey), 158.0);
+
+    // Tap to collapse the ExpansionTile.
+    await tester.tap(find.text('title'));
+    await tester.pumpAndSettle();
+
+    // Override the animation duration.
+    await tester.pumpWidget(buildExpansionTile(animationStyle: AnimationStyle(duration: const Duration(milliseconds: 800))));
+    await tester.pumpAndSettle();
+
+    // Test the overridden animation duration.
+    await tester.tap(find.text('title'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 200)); // Advance the animation by 1/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(67.4, 0.1));
+
+    await tester.pump(const Duration(milliseconds: 200)); // Advance the animation by 2/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(89.6, 0.1));
+
+    await tester.pumpAndSettle(); // Advance the animation to the end.
+
+    expect(getHeight(expansionTileKey), 158.0);
+
+    // Tap to collapse the ExpansionTile.
+    await tester.tap(find.text('title'));
+    await tester.pumpAndSettle();
+
+    // Override the animation curve.
+    await tester.pumpWidget(buildExpansionTile(animationStyle: AnimationStyle(curve: Easing.emphasizedDecelerate)));
+    await tester.pumpAndSettle();
+
+    // Test the overridden animation curve.
+    await tester.tap(find.text('title'));
+    await tester.pump();
+    await tester.pump(const Duration(milliseconds: 50)); // Advance the animation by 1/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(141.2, 0.1));
+
+    await tester.pump(const Duration(milliseconds: 50)); // Advance the animation by 2/4 of its duration.
+
+    expect(getHeight(expansionTileKey), closeTo(153, 0.1));
+
+    await tester.pumpAndSettle(); // Advance the animation to the end.
+
+    expect(getHeight(expansionTileKey), 158.0);
+
+    // Tap to collapse the ExpansionTile.
+    await tester.tap(find.text('title'));
+
+    // Test no animation.
+    await tester.pumpWidget(buildExpansionTile(animationStyle: AnimationStyle.noAnimation));
+
+    // Tap to expand the ExpansionTile.
+    await tester.tap(find.text('title'));
+    await tester.pump();
+
+    expect(getHeight(expansionTileKey), 158.0);
+  });
 }