Script to update tester files during integration

.gitignore

@@ -44,6 +44,9 @@ package-lock.json
 *BundleArtifacts*
 *ReactAssets*
 
+# RN Tester sync cache (created by scripts/sync-rn-tester.ps1)
+.rn-cache/
+
 #OS junk files
 [Tt]humbs.db
 *.DS_Store

scripts/README.md

@@ -0,0 +1,103 @@
+# RNTester Sync Script
+
+A PowerShell script that syncs React Native Windows files with upstream React Native commits. Fixes `yarn validate-overrides` errors and keeps IntegrationTests up to date.
+
+## 🎯 What It Does
+
+**Syncs TWO things from upstream React Native:**
+1. **RNTester files** → `packages/@react-native/tester/js/` (fixes yarn validate-overrides)
+2. **IntegrationTests** → `vnext/ReactCopies/IntegrationTests/` (keeps tests current)
+
+**Uses the commit hash YOU provide** - so you control exactly which React Native version to sync from.
+
+## 🚀 Quick Start
+
+```powershell
+# Preview what will change (recommended first)
+.\scripts\sync-rn-tester.ps1 -CommitHash '1a6d466f1' -DryRun
+
+# Apply the changes
+.\scripts\sync-rn-tester.ps1 -CommitHash '1a6d466f1'
+
+# Verify it worked
+yarn validate-overrides
+```
+
+## 📖 Usage
+
+### Basic Command
+```powershell
+.\sync-rn-tester.ps1 -CommitHash <your-commit-hash>
+```
+
+### Options
+- `-CommitHash` (required) - React Native commit to sync from
+- `-DryRun` - Preview changes without modifying files
+- `-ForceClone` - Force fresh download (if cache issues)
+
+## 🔍 Finding the Right Commit Hash
+
+### From GitHub Compare URL
+```
+https://github.com/facebook/react-native/compare/old...NEW
+Use the NEW commit hash (after the ...)
+Example: 1a6d466f1
+```
+
+### From Command Line
+```bash
+git ls-remote https://github.com/facebook/react-native.git main
+```
+
+### From GitHub Web
+Visit: https://github.com/facebook/react-native/commits/main
+
+## ⚡ Performance
+
+- **First run**: Downloads React Native (~30-60 seconds)
+- **Later runs**: Uses cache (~5-10 seconds)
+- **Cache location**: `[YourRepoParent]/.rn-cache/`
+
+## 🛡️ Safety
+
+- **Preview mode**: Use `-DryRun` to see changes first
+- **Git tracked**: All changes show up in `git diff`
+- **Limited scope**: Only touches RNTester and IntegrationTests
+- **Auto-detection**: Finds your repo automatically
+
+## 💡 Common Workflow
+
+```powershell
+# 1. Save your work
+git add . && git commit -m "checkpoint before sync"
+
+# 2. Preview the sync
+.\scripts\sync-rn-tester.ps1 -CommitHash 'TARGET_COMMIT' -DryRun
+
+# 3. Apply the sync  
+.\scripts\sync-rn-tester.ps1 -CommitHash 'TARGET_COMMIT'
+
+# 4. Verify and commit
+yarn validate-overrides
+git add . && git commit -m "sync: RNTester with TARGET_COMMIT"
+```
+
+## 🔧 Troubleshooting
+
+**"Could not auto-detect repository root"**
+→ Run from inside react-native-windows directory
+
+**"Failed to checkout commit"**  
+→ Try: `.\sync-rn-tester.ps1 -CommitHash 'abc123' -ForceClone`
+
+**yarn validate-overrides still fails**
+→ Double-check the commit hash is correct
+
+## 📁 What Gets Modified
+
+✅ **Modified**: RNTester examples and IntegrationTests only  
+❌ **Never touched**: Your app code, Windows native code, build files
+
+---
+
+**That's it!** Simple script, one mode, syncs both areas you need for React Native Windows integration work.