Update BottomSheet test for M3 + fix an issue in elevation resolution (#136071)

This PR updates unit tests from bottom sheet tests for M3 migration.

More info in https://github.com/flutter/flutter/issues/127064

It also contains in bottom_sheet.dart where a default value took precedence over a theme attribute.

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

@@ -1071,7 +1071,7 @@ class ModalBottomSheetRoute<T> extends PopupRoute<T> {
           return _ModalBottomSheet<T>(
             route: this,
             backgroundColor: backgroundColor ?? sheetTheme.modalBackgroundColor ?? sheetTheme.backgroundColor ?? defaults.backgroundColor,
-            elevation: elevation ?? sheetTheme.modalElevation ?? defaults.modalElevation ?? sheetTheme.elevation,
+            elevation: elevation ?? sheetTheme.modalElevation ?? sheetTheme.elevation ?? defaults.modalElevation,
             shape: shape,
             clipBehavior: clipBehavior,
             constraints: constraints,

packages/flutter/test/material/bottom_sheet_theme_test.dart

@@ -79,7 +79,34 @@ void main() {
     ]);
   });
 
-  testWidgetsWithLeakTracking('Passing no BottomSheetThemeData returns defaults', (WidgetTester tester) async {
+  testWidgetsWithLeakTracking('Material3 - Passing no BottomSheetThemeData returns defaults', (WidgetTester tester) async {
+    await tester.pumpWidget(MaterialApp(
+      theme: ThemeData(useMaterial3: true),
+      home: Scaffold(
+        body: BottomSheet(
+          onClosing: () {},
+          builder: (BuildContext context) {
+            return Container();
+          },
+        ),
+      ),
+    ));
+
+    final Material material = tester.widget<Material>(
+      find.descendant(
+        of: find.byType(BottomSheet),
+        matching: find.byType(Material),
+      ),
+    );
+
+    final ThemeData theme = Theme.of(tester.element(find.byType(Scaffold)));
+    expect(material.color, theme.colorScheme.surface);
+    expect(material.elevation, 1.0);
+    expect(material.shape, const RoundedRectangleBorder(borderRadius: BorderRadius.vertical(top: Radius.circular(28.0))));
+    expect(material.clipBehavior, Clip.none);
+  });
+
+  testWidgetsWithLeakTracking('Material2 - Passing no BottomSheetThemeData returns defaults', (WidgetTester tester) async {
     await tester.pumpWidget(MaterialApp(
       theme: ThemeData(useMaterial3: false),
       home: Scaffold(
@@ -227,7 +254,7 @@ void main() {
     expect(material.color, persistentBackgroundColor);
   });
 
-  testWidgetsWithLeakTracking("Modal bottom sheet-specific parameters don't apply to persistent bottom sheets", (WidgetTester tester) async {
+  testWidgetsWithLeakTracking("Material3 - Modal bottom sheet-specific parameters don't apply to persistent bottom sheets", (WidgetTester tester) async {
     const double modalElevation = 5.0;
     const Color modalBackgroundColor = Colors.yellow;
     const BottomSheetThemeData bottomSheetTheme = BottomSheetThemeData(
@@ -239,6 +266,29 @@ void main() {
     await tester.tap(find.text('Show Persistent'));
     await tester.pumpAndSettle();
 
+    final Material material = tester.widget<Material>(
+      find.descendant(
+        of: find.byType(BottomSheet),
+        matching: find.byType(Material),
+      ),
+    );
+    expect(material.elevation, 1.0);
+    final ThemeData theme = Theme.of(tester.element(find.byType(Scaffold)));
+    expect(material.color, theme.colorScheme.surface);
+  });
+
+  testWidgetsWithLeakTracking("Material2 - Modal bottom sheet-specific parameters don't apply to persistent bottom sheets", (WidgetTester tester) async {
+    const double modalElevation = 5.0;
+    const Color modalBackgroundColor = Colors.yellow;
+    const BottomSheetThemeData bottomSheetTheme = BottomSheetThemeData(
+      modalElevation: modalElevation,
+      modalBackgroundColor: modalBackgroundColor,
+    );
+
+    await tester.pumpWidget(bottomSheetWithElevations(bottomSheetTheme, useMaterial3: false));
+    await tester.tap(find.text('Show Persistent'));
+    await tester.pumpAndSettle();
+
     final Material material = tester.widget<Material>(
       find.descendant(
         of: find.byType(BottomSheet),
@@ -258,14 +308,14 @@ void main() {
     const Color darkShadowColor = Colors.purple;
 
     await tester.pumpWidget(MaterialApp(
-      theme: ThemeData.light(useMaterial3: false).copyWith(
+      theme: ThemeData.light().copyWith(
         bottomSheetTheme: const BottomSheetThemeData(
           elevation: lightElevation,
           backgroundColor: lightBackgroundColor,
           shadowColor: lightShadowColor,
         ),
       ),
-      darkTheme: ThemeData.dark(useMaterial3: false).copyWith(
+      darkTheme: ThemeData.dark().copyWith(
         bottomSheetTheme: const BottomSheetThemeData(
           elevation: darkElevation,
           backgroundColor: darkBackgroundColor,
@@ -323,9 +373,9 @@ void main() {
   });
 }
 
-Widget bottomSheetWithElevations(BottomSheetThemeData bottomSheetTheme) {
+Widget bottomSheetWithElevations(BottomSheetThemeData bottomSheetTheme, {bool useMaterial3 = true}) {
   return MaterialApp(
-    theme: ThemeData(bottomSheetTheme: bottomSheetTheme, useMaterial3: false),
+    theme: ThemeData(bottomSheetTheme: bottomSheetTheme, useMaterial3: useMaterial3),
     home: Scaffold(
       body: Builder(
         builder: (BuildContext context) {