test: add node extension test

frontend/app_flowy/packages/appflowy_editor/test/extensions/node_extension_test.dart

@@ -0,0 +1,31 @@
+import 'dart:ui';
+
+import 'package:appflowy_editor/appflowy_editor.dart';
+import 'package:flutter_test/flutter_test.dart';
+import 'package:mockito/mockito.dart';
+import 'package:appflowy_editor/src/extensions/node_extensions.dart';
+
+class MockNode extends Mock implements Node {}
+
+void main() {
+  group('NodeExtensions::', () {
+    final mockNode = MockNode();
+
+    final selection = Selection(
+      start: Position(path: [0, 1]),
+      end: Position(path: [1, 0]),
+    );
+
+    test('rect - renderBox is null', () {
+      when(mockNode.renderBox).thenReturn(null);
+      final result = mockNode.rect;
+      expect(result, Rect.zero);
+    });
+
+    // test('inSelection', () {
+    //   when(mockNode.path).thenAnswer((_) => [3, 3]);
+    //   final result = mockNode.inSelection(selection);
+    //   expect(result, true);
+    // });
+  });
+}