`Could not patch module system` on blank Expo RN project

[samchencode]

Describe the bug

What I'm doing

Following the quick start guide with a new Expo React Native app, blank template. I'm running iOS 26.1 on Simulator.

I built and ran the app as ios bundle with npx expo run:ios and then ran npx react-native-harness --harnessRunner ios. This results in an error port 8081 is not available. So I turn off the expo dev server which occupies 8081. Then I get Could not patch module system

What I expect

I copied the tests in the quick start into __tests__/example.harness.js

I expect the tests in example.harness.js to run and pass

What is happening

I get error Could not patch module system

Output

npx react-native-harness --harnessRunner ios
 HARNESS  Preparing to run tests using ios runner

Test Suites: 0 of 1 total
Tests:       0 total
Snapshots:   0 total
Time:        0.072 s
Ran all test suites.
 HARNESS  Metro port 8081 is not available

npx react-native-harness --harnessRunner ios
 HARNESS  Preparing to run tests using ios runner

Test Suites: 0 of 1 total
Tests:       0 total
Snapshots:   0 total
Time:        0.299 s
Ran all test suites.
CouldNotPatchModuleSystemError: Could not patch module system
    at getMetroConfigPath (/Volumes/jaunty/programming/tinker/fiddle-expo-blank/node_modules/@react-native-harness/metro/dist/moduleSystem.js:22:11)
    at getMetroDefaultsPath (/Volumes/jaunty/programming/tinker/fiddle-expo-blank/node_modules/@react-native-harness/metro/dist/moduleSystem.js:25:29)
    at patchModuleSystem (/Volumes/jaunty/programming/tinker/fiddle-expo-blank/node_modules/@react-native-harness/metro/dist/moduleSystem.js:37:29)
    at /Volumes/jaunty/programming/tinker/fiddle-expo-blank/node_modules/@react-native-harness/metro/dist/withRnHarness.js:21:46
    at process.processTicksAndRejections (node:internal/process/task_queues:105:5)
    at async getMetroInstance (file:///Volumes/jaunty/programming/tinker/fiddle-expo-blank/node_modules/@react-native-harness/bundler-metro/dist/factory.js:38:20)
    at async Promise.all (index 0)
    at async getHarnessInternal (file:///Volumes/jaunty/programming/tinker/fiddle-expo-blank/node_modules/@react-native-harness/jest/dist/harness.js:7:61)
    at async getHarness (file:///Volumes/jaunty/programming/tinker/fiddle-expo-blank/node_modules/@react-native-harness/jest/dist/harness.js:63:25)
    at async setup (file:///Volumes/jaunty/programming/tinker/fiddle-expo-blank/node_modules/@react-native-harness/jest/dist/setup.js:47:21)

System Info

npx react-native info                       
info Fetching system and libraries information...
System:
  OS: macOS 26.2
  CPU: (8) arm64 Apple M1
  Memory: 97.95 MB / 8.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.12.0
    path: /Users/bapspaf/.nvm/versions/node/v22.12.0/bin/node
  Yarn:
    version: 1.22.22
    path: /Users/bapspaf/.nvm/versions/node/v22.12.0/bin/yarn
  npm:
    version: 10.9.0
    path: /Users/bapspaf/.nvm/versions/node/v22.12.0/bin/npm
  Watchman: Not Found
Managers:
  CocoaPods:
    version: 1.16.2
    path: /opt/homebrew/bin/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.1
      - iOS 26.1
      - macOS 26.1
      - tvOS 26.1
      - visionOS 26.1
      - watchOS 26.1
  Android SDK: Not Found
IDEs:
  Android Studio: 2025.2 AI-252.27397.103.2522.14514259
  Xcode:
    version: 26.1/17B55
    path: /usr/bin/xcodebuild
Languages:
  Java: Not Found
  Ruby:
    version: 2.6.10
    path: /usr/bin/ruby
npmPackages:
  "@react-native-community/cli":
    installed: 20.0.2
    wanted: ^20.0.2
  react:
    installed: 19.1.0
    wanted: 19.1.0
  react-native:
    installed: 0.81.5
    wanted: 0.81.5
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: true
  newArchEnabled: true

info React Native v0.83.0 is now available (your project is running on v0.81.5).
info Changelog: https://github.com/facebook/react-native/releases/tag/v0.83.0
info Diff: https://react-native-community.github.io/upgrade-helper/?from=0.81.5&to=0.83.0
info For more info, check out "https://reactnative.dev/docs/upgrading?os=macos".

React Native Harness Version

1.0.0-alpha.19

Reproduction

https://github.com/samchencode/bug-report-expo-harness

Steps to reproduce

1. Create iOS Simulator Device (iPhone 14 Pro) named i6.7 with iOS 26.1
2. npm install
3. npx expo run:ios
4. npx react-native-harness --harnessRunner ios