[SuperEditor] Add test to demonstrate that changing layer builders does not re-layout

super_editor/test/super_editor/supereditor_theme_switching_test.dart

@@ -0,0 +1,103 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter_test_runners/flutter_test_runners.dart';
+import 'package:super_editor/super_editor.dart';
+import 'package:super_editor/super_editor_test.dart';
+
+import 'test_documents.dart';
+
+void main() {
+  group('SuperEditor > theme switching', () {
+    testWidgetsOnArbitraryDesktop('switches caret color', (tester) async {
+      final brightnessNotifier = ValueNotifier<Brightness>(Brightness.light);
+
+      await _pumpThemeSwitchingTestApp(tester, brightnessNotifier: brightnessNotifier);
+
+      // Place the caret at the beginning of the paragraph.
+      await tester.placeCaretInParagraph('1', 0);
+
+      // Ensure the caret is green, because the theme is light.
+      expect(_findDesktopCaretColor(tester), Colors.green.shade500);
+
+      // Switch the theme to dark.
+      brightnessNotifier.value = Brightness.dark;
+      await tester.pumpAndSettle();
+
+      // Ensure the caret is red, because the theme is dark.
+      expect(_findDesktopCaretColor(tester), Colors.red.shade500);
+    });
+
+    testWidgetsOnArbitraryDesktop('switches caret color after typing', (tester) async {
+      final brightnessNotifier = ValueNotifier<Brightness>(Brightness.light);
+
+      await _pumpThemeSwitchingTestApp(tester, brightnessNotifier: brightnessNotifier);
+
+      // Place the caret at the beginning of the paragraph.
+      await tester.placeCaretInParagraph('1', 0);
+
+      // Ensure the caret is green, because the theme is light.
+      expect(_findDesktopCaretColor(tester), Colors.green.shade500);
+
+      // Switch the theme to dark.
+      brightnessNotifier.value = Brightness.dark;
+      await tester.pumpAndSettle();
+
+      // Type a character to trigger a re-layout.
+      await tester.typeImeText('a');
+
+      // Ensure the caret is red, because the theme is dark.
+      expect(_findDesktopCaretColor(tester), Colors.red.shade500);
+    });
+  });
+}
+
+/// Pumps a widget tree that rebuilds when the [brightnessNotifier] changes.
+///
+/// The widget tree contains a [SuperEditor] with a custom caret overlay that
+/// changes color based on the brightness of the theme.
+Future<void> _pumpThemeSwitchingTestApp(
+  WidgetTester tester, {
+  required ValueNotifier<Brightness> brightnessNotifier,
+}) async {
+  final composer = MutableDocumentComposer();
+  final editor = createDefaultDocumentEditor(
+    document: singleParagraphDoc(),
+    composer: composer,
+  );
+
+  await tester.pumpWidget(
+    MaterialApp(
+      home: Scaffold(
+        body: ValueListenableBuilder(
+          valueListenable: brightnessNotifier,
+          builder: (context, brightness, child) {
+            return Theme(
+              data: ThemeData(
+                brightness: brightness,
+              ),
+              child: SuperEditor(
+                editor: editor,
+                documentOverlayBuilders: [
+                  // Copy all default overlay builders except the caret overlay builder.
+                  ...defaultSuperEditorDocumentOverlayBuilders.where(
+                    (builder) => builder is! DefaultCaretOverlayBuilder,
+                  ),
+                  DefaultCaretOverlayBuilder(
+                    caretStyle: CaretStyle(
+                      color: brightness == Brightness.light ? Colors.green : Colors.red,
+                    ),
+                  )
+                ],
+              ),
+            );
+          },
+        ),
+      ),
+    ),
+  );
+}
+
+Color _findDesktopCaretColor(WidgetTester tester) {
+  final caret = tester.widget<Container>(find.byKey(DocumentKeys.caret));
+  return (caret.decoration as BoxDecoration).color!;
+}