[flutter_markdown] test for custom font feature

packages/flutter_markdown/test/footnote_test.dart

@@ -158,7 +158,7 @@ void defineTests() {
     'superscript textstyle replacing',
     () {
       testWidgets(
-        'superscript has correct fontfeature',
+        'superscript has correct default fontfeature',
         (WidgetTester tester) async {
           const String data = 'Foo[^a]\n[^a]: Bar';
           await tester.pumpWidget(
@@ -184,6 +184,35 @@ void defineTests() {
         },
       );
 
+      testWidgets(
+        'superscript has correct custom fontfeature',
+        (WidgetTester tester) async {
+          const String data = 'Foo[^a]\n[^a]: Bar';
+          await tester.pumpWidget(
+            boilerplate(
+              MarkdownBody(
+                data: data,
+                styleSheet:
+                    MarkdownStyleSheet(superscriptFontFeatureTag: 'numr'),
+              ),
+            ),
+          );
+
+          final Iterable<Widget> widgets = tester.allWidgets;
+          final RichText richText = widgets
+              .firstWhere((Widget widget) => widget is RichText) as RichText;
+
+          final TextSpan span = richText.text as TextSpan;
+          final List<InlineSpan>? children = span.children;
+
+          expect(children, isNotNull);
+          expect(children!.length, 2);
+          expect(children[1].style, isNotNull);
+          expect(children[1].style!.fontFeatures?.length, 2);
+          expect(children[1].style!.fontFeatures?[1].feature, 'numr');
+        },
+      );
+
       testWidgets(
         'superscript index has the same font style like text',
         (WidgetTester tester) async {