test: migrate page up and down

example/lib/pages/simple_editor.dart

@@ -158,6 +158,10 @@ class SimpleEditor extends StatelessWidget {
         outdentCommand,
 
         exitEditingCommand,
+
+        //
+        pageUpCommand,
+        pageDownCommand,
       ],
     );
   }

lib/src/editor/editor_component/service/shortcuts/command_shortcut_events/page_down_command.dart

@@ -25,7 +25,7 @@ CommandShortcutEventHandler _pageUpCommandHandler = (editorState) {
 
   final scrollHeight = scrollService.onePageHeight;
   final dy = scrollService.dy;
-  if (dy <= 0 || scrollHeight == null) {
+  if (dy < 0 || scrollHeight == null) {
     return KeyEventResult.ignored;
   }
   scrollService.scrollTo(

test/new/infra/testable_editor.dart

@@ -109,6 +109,10 @@ class TestableEditor {
         outdentCommand,
 
         exitEditingCommand,
+
+        //
+        pageUpCommand,
+        pageDownCommand,
       ],
     );
     await tester.pumpWidget(

test/service/internal_key_event_handlers/page_up_down_handler_test.dart

@@ -1,7 +1,7 @@
 import 'package:appflowy_editor/appflowy_editor.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
-import '../../infra/test_editor.dart';
+import '../../new/infra/testable_editor.dart';
 
 void main() async {
   setUpAll(() {
@@ -12,38 +12,26 @@ void main() async {
     testWidgets('Presses PageUp and pageDown key in large document',
         (tester) async {
       const text = 'Welcome to Appflowy 😁';
-      final editor = tester.editor;
+      final editor = tester.editor..addParagraphs(1000, initialText: text);
-      for (var i = 0; i < 1000; i++) {
-        editor.insertTextNode(text);
-      }
       await editor.startTesting();
       await editor.updateSelection(
         Selection.single(path: [0], startOffset: 0),
       );
 
-      final scrollService = editor.editorState.service.scrollService;
+      final scrollService = editor.editorState.service.scrollService!;
-
+      final page = scrollService.page!;
-      expect(scrollService != null, true);
+      final onePageHeight = scrollService.onePageHeight!;
-
-      if (scrollService == null) {
-        return;
-      }
-
-      final page = scrollService.page;
-      final onePageHeight = scrollService.onePageHeight;
-      expect(page != null, true);
-      expect(onePageHeight != null, true);
 
       // Pressing the pageDown key continuously.
       var currentOffsetY = 0.0;
-      for (int i = 1; i <= page!; i++) {
+      for (int i = 1; i <= page; i++) {
         await editor.pressLogicKey(
           key: LogicalKeyboardKey.pageDown,
         );
         if (i == page) {
           currentOffsetY = scrollService.maxScrollExtent;
         } else {
-          currentOffsetY += onePageHeight!;
+          currentOffsetY += onePageHeight;
         }
         final dy = scrollService.dy;
         expect(dy, currentOffsetY);
@@ -65,9 +53,9 @@ void main() async {
         if (i == 1) {
           currentOffsetY = scrollService.minScrollExtent;
         } else {
-          currentOffsetY -= onePageHeight!;
+          currentOffsetY -= onePageHeight;
         }
-        final dy = editor.editorState.service.scrollService?.dy;
+        final dy = scrollService.dy;
         expect(dy, currentOffsetY);
       }