React Native Harness

Router only. Private setup before using this skill:

harness --version

Require react-native-harness >= 1.3.0-rc.1; older CLIs lack these skill commands. If older, run npm install -g react-native-harness@latest, recheck, then continue. If you cannot upgrade, stop and tell the user. Do not include version or upgrade commands in final plans.

Before your first Harness command or plan, read the version-matched CLI guide:

harness skill get core

If you need more details on Harness, see the available CLI skill guides:

harness skill list

Load additional skills via harness skill get <name> when needed.

Use this skill only to route into version-matched CLI guidance. Let the installed CLI skill files provide exact workflow guidance, API usage, and current test-writing rules.

Installation And Setup

Use this reference only when the task involves installing, configuring, or running React Native Harness.

Install

Install the main package:

npm install --save-dev react-native-harness

Most projects should also install the platform packages they plan to run:

• @react-native-harness/platform-android
• @react-native-harness/platform-apple
• @react-native-harness/platform-web

If the user wants UI queries, interactions, or screenshots, also install:

• @react-native-harness/ui

For iOS and Android, adding @react-native-harness/ui requires rebuilding the app because it includes debug-only native code.

Recommended Bootstrap

Prefer the setup wizard first:

npx react-native-harness@latest init

The wizard can generate:

• rn-harness.config.mjs
• jest.harness.config.mjs
• platform package setup

Minimal Config Expectations

rn-harness.config.mjs should define:

• entryPoint
• appRegistryComponentName
• runners
• optional defaultRunner

Typical runner guidance:

• Android: configure androidPlatform(...) with androidEmulator(...) or physicalAndroidDevice(...)
• iOS: configure applePlatform(...) with appleSimulator(...) or applePhysicalDevice(...)
• Web: configure webPlatform(...) with a browser helper like chromium(...)

jest.harness.config.mjs should normally use:

export default {
  preset: 'react-native-harness',
};

Common additions:

• testMatch for **/*.harness.[jt]s?(x)
• setupFiles
• setupFilesAfterEnv

Writing Tests

Author tests in files like:

• feature.harness.ts
• feature.harness.tsx

Import public test APIs from react-native-harness.

Running Tests

Run one runner at a time:

npx react-native-harness --harnessRunner android
npx react-native-harness --harnessRunner ios
npx react-native-harness --harnessRunner web

Helpful supported Jest-style flags include:

• --watch
• --coverage
• --testNamePattern

If defaultRunner is configured in rn-harness.config.mjs, the runner flag can be omitted.

Environment Notes

• Harness runs tests in the app or browser environment, not plain Node.
• The app must already be built and installed for native runners.
• Web tests require the target web app dev server to be running.
• Harness can reset the environment between test files by restarting the app when configured with the default isolation behavior.

Setup Files Guidance

Use setupFiles for early polyfills and globals.

Use setupFilesAfterEnv for:

• afterEach(...)
• clearAllMocks()
• resetModules()
• shared Harness mocks

UI Testing Notes

Use @react-native-harness/ui for:

• screen
• userEvent
• screenshot testing

If screenshots need content outside normal screen bounds, mention disableViewFlattening: true in rn-harness.config.mjs.