React Native Harness is a testing framework designed to bring Jest-like developer experience to real native execution environments. It allows developers to write familiar JavaScript tests using APIs such as describe, it, expect, beforeEach, and afterEach, while executing those tests directly on iOS simulators, Android emulators, or web environments.

Unlike traditional Jest tests that run in a Node.js environment without access to native APIs, Harness executes tests where the actual native modules exist. This makes it particularly useful for validating TurboModules and other native functionality in realistic runtime conditions.

The framework is designed to bridge the gap between fast unit testing and slower end-to-end testing by providing a middle ground: fast execution with real device or emulator context. It supports TypeScript, CI/CD integration, and straightforward setup in existing React Native projects.

React Native Harness is especially valuable for teams building native modules or complex React Native applications that require reliable validation of platform-specific behavior without the overhead of full E2E test frameworks.

Key features include:

• Jest-style test syntax for React Native applications
• Execution on real iOS simulators, Android emulators, and web
• Direct access to native modules during testing
• Fast alternative to full end-to-end testing frameworks
• TypeScript support and CI/CD integration

Common use cases include:

• Testing React Native native modules
• Validating platform-specific behavior
• Running integration-style tests in real environments
• Improving test reliability over mocked environments
• Accelerating React Native CI pipelines

React Native Harness is developed by Callstack as an open-source testing framework focused on improving native testing workflows in React Native ecosystems.