#CLI Reference

The react-native-harness command is a powerful wrapper around the Jest CLI. It provides seamless integration with native environments while maintaining the familiar Jest developer experience.

#Commands

#init

Runs the interactive setup wizard to configure React Native Harness in your project.

npx react-native-harness init

The wizard will help you:

• Detect your project type (Expo or React Native CLI).
• Install required platform packages.
• Configure Android, iOS, or Web runners.
• Generate configuration files (rn-harness.config.mjs and jest.harness.config.mjs).

#(default)

Runs tests using the Harness test runner.

npx react-native-harness [test-file-pattern] [options]

#Options

#Harness Specific Flags

#Running on Multiple Platforms

Harness executes tests on a single runner at a time to ensure isolated and reliable reporting. To run tests on multiple platforms (e.g., both iOS and Android in CI), you must execute the command separately for each runner:

# Run Android tests
npx react-native-harness --harnessRunner android

# Run iOS tests
npx react-native-harness --harnessRunner ios

#Supported Jest Flags

React Native Harness supports the most commonly used Jest flags:

• --watch: Watch files for changes and rerun tests related to changed files.
• --coverage: Indicates that test coverage information should be collected and reported in the output.
• --testNamePattern, -t: Run only tests with a name that matches the regex.
• --testPathPattern: A regexp string that is matched against all tests paths before executing the test.
• --verbose: Display individual test results with the test suite hierarchy.

#Restrictions and Limitations

To ensure stability and compatibility with real native devices, React Native Harness disables or restricts certain standard Jest CLI options.

#Forced Serial Execution

Harness executes tests serially (one at a time) on the target device to prevent native resource conflicts (like multiple tests trying to access the camera or filesystem simultaneously).

The following Jest flags are ignored or disabled:

• --maxWorkers
• --runInBand (Implicitly always true)
• --maxConcurrency
• --shard

#Restricted Configuration Overrides

Harness manages the test environment, transformation, and module resolution internally to ensure tests can be bundled by Metro and run on-device.

The following Jest configuration flags are disabled:

• --runner / --testRunner
• --testEnvironment
• --preset
• --transform / --transformIgnorePatterns
• --resolver
• --globals

#Snapshot Management

Snapshot testing for UI is handled via the separate @react-native-harness/ui package and the toMatchImageSnapshot matcher. Standard Jest snapshot flags like --updateSnapshot (-u) are currently not supported for native image snapshots.