From 160f0cd4f3cb5171fbfdda97a7ffcd1f4a5df5b0 Mon Sep 17 00:00:00 2001
From: Fabrizio Duroni <fabrizio.duroni@gmail.com>
Date: Tue, 28 Apr 2026 00:13:32 +0200
Subject: [PATCH 1/2] refactor(test): re-enable test for retain batch region
 weh item append (react 19 differen)

Co-authored-by: Copilot <copilot@github.com>
---
 .../Lists/__tests__/VirtualizedList-test.js   | 27 ++++++++++++++-----
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/packages/virtualized-lists/Lists/__tests__/VirtualizedList-test.js b/packages/virtualized-lists/Lists/__tests__/VirtualizedList-test.js
index b02757cadf9..2c79bc843a0 100644
--- a/packages/virtualized-lists/Lists/__tests__/VirtualizedList-test.js
+++ b/packages/virtualized-lists/Lists/__tests__/VirtualizedList-test.js
@@ -1836,8 +1836,7 @@ it('retains initial render region when an item is appended', async () => {
   expect(component).toMatchSnapshot();
 });
 
-// TODO: Revisit this test case after upgrading to React 19.
-skipTestSilenceLinter(
+it(
   'retains batch render region when an item is appended',
   async () => {
     const items = generateItems(10);
@@ -1860,12 +1859,9 @@ skipTestSilenceLinter(
         viewport: {width: 10, height: 50},
         content: {width: 10, height: 100},
       });
-      performAllBatches();
     });
 
-    await act(async () => {
-      await jest.runAllTimersAsync();
-    });
+    await advanceUntilLastCellIndexRendered(component, items.length - 1);
 
     await act(() => {
       component.update(
@@ -2639,13 +2635,30 @@ async function advanceUntilRenderAreaChanged(component) {
     }
 
     await act(() => {
-      jest.advanceTimersToNextTimer(1);
+      performNextBatch();
     });
   }
 
   throw new Error(`Render area did not change`);
 }
 
+async function advanceUntilLastCellIndexRendered(component, targetLastIndex) {
+  const instance = component.getInstance();
+  const MAX_TIMER_STEPS = 20;
+
+  for (let step = 0; step < MAX_TIMER_STEPS; step++) {
+    if (instance.state.cellsAroundViewport.last === targetLastIndex) {
+      return;
+    }
+
+    await act(() => {
+      performNextBatch();
+    });
+  }
+
+  throw new Error(`Target last index ${targetLastIndex} not rendered`);
+}
+
 function performAllBatches() {
   jest.runAllTimers();
 }

From a7a6905fce46531b4ac3dd1c1e471a4bc5a6a600 Mon Sep 17 00:00:00 2001
From: Fabrizio Duroni <fabrizio.duroni@gmail.com>
Date: Wed, 29 Apr 2026 21:32:45 +0200
Subject: [PATCH 2/2] chore: linting

---
 .../Lists/__tests__/VirtualizedList-test.js   | 77 +++++++++----------
 1 file changed, 37 insertions(+), 40 deletions(-)

diff --git a/packages/virtualized-lists/Lists/__tests__/VirtualizedList-test.js b/packages/virtualized-lists/Lists/__tests__/VirtualizedList-test.js
index 2c79bc843a0..6fe771ea183 100644
--- a/packages/virtualized-lists/Lists/__tests__/VirtualizedList-test.js
+++ b/packages/virtualized-lists/Lists/__tests__/VirtualizedList-test.js
@@ -1836,52 +1836,49 @@ it('retains initial render region when an item is appended', async () => {
   expect(component).toMatchSnapshot();
 });
 
-it(
-  'retains batch render region when an item is appended',
-  async () => {
-    const items = generateItems(10);
-    const ITEM_HEIGHT = 10;
+it('retains batch render region when an item is appended', async () => {
+  const items = generateItems(10);
+  const ITEM_HEIGHT = 10;
 
-    let component;
-    await act(() => {
-      component = create(
-        <VirtualizedList
-          initialNumToRender={1}
-          maxToRenderPerBatch={1}
-          {...baseItemProps(items)}
-          {...fixedHeightItemLayoutProps(ITEM_HEIGHT)}
-        />,
-      );
-    });
+  let component;
+  await act(() => {
+    component = create(
+      <VirtualizedList
+        initialNumToRender={1}
+        maxToRenderPerBatch={1}
+        {...baseItemProps(items)}
+        {...fixedHeightItemLayoutProps(ITEM_HEIGHT)}
+      />,
+    );
+  });
 
-    await act(() => {
-      simulateLayout(component, {
-        viewport: {width: 10, height: 50},
-        content: {width: 10, height: 100},
-      });
+  await act(() => {
+    simulateLayout(component, {
+      viewport: {width: 10, height: 50},
+      content: {width: 10, height: 100},
     });
+  });
 
-    await advanceUntilLastCellIndexRendered(component, items.length - 1);
+  await advanceUntilLastCellIndexRendered(component, items.length - 1);
 
-    await act(() => {
-      component.update(
-        <VirtualizedList
-          initialNumToRender={1}
-          maxToRenderPerBatch={1}
-          {...baseItemProps(items)}
-          {...fixedHeightItemLayoutProps(ITEM_HEIGHT)}
-          data={generateItems(11)}
-        />,
-      );
-    });
+  await act(() => {
+    component.update(
+      <VirtualizedList
+        initialNumToRender={1}
+        maxToRenderPerBatch={1}
+        {...baseItemProps(items)}
+        {...fixedHeightItemLayoutProps(ITEM_HEIGHT)}
+        data={generateItems(11)}
+      />,
+    );
+  });
 
-    // Adding an item to the list after batch render should keep the existing
-    // rendered items rendered. We batch render 10 items, then add an 11th. Expect
-    // the first ten items to be present, with a spacer for the 11th until the
-    // next batch render.
-    expect(component).toMatchSnapshot();
-  },
-);
+  // Adding an item to the list after batch render should keep the existing
+  // rendered items rendered. We batch render 10 items, then add an 11th. Expect
+  // the first ten items to be present, with a spacer for the 11th until the
+  // next batch render.
+  expect(component).toMatchSnapshot();
+});
 
 it('constrains batch render region when an item is removed', async () => {
   const items = generateItems(10);