Write Once, Test Everywhere: Cross-Platform Testing for React Native
Write Once, Test Everywhere: Cross-Platform Testing for React Native
Cross-platform testing in React Native made simple: a lightweight architecture to run and extend tests on any JavaScript-powered platform.
Write Once, Test Everywhere: Cross-Platform Testing for React Native
Testing React Native apps has always meant choosing between speed and realism. Jest is fast, familiar, and great for unit tests; but it runs in Node.js with mocks for native modules. End-to-end frameworks give you realism, but at the cost of setup, maintenance, and slow pipelines.
At React Alicante 2025, Łukasz Chludziński introduces React Native Harness, a new testing framework created by Szymon Chmal at Callstack. Harness runs Jest-style tests directly on real devices and simulators, with full access to native modules and no mocks by default.
You'll see:
- How Harness plugs into Metro to run tests inside the real runtime
- Testing native libraries like MMKV without custom runners or hacks
- Verifying spec compliance for APIs like fetch and WebSocket
- How developers can keep their familiar Jest DX while gaining native access
- Why this fills the "missing middle ground" between unit tests and E2E
Write Once, Test Everywhere: Cross-Platform Testing for React Native
Cross-platform testing in React Native made simple: a lightweight architecture to run and extend tests on any JavaScript-powered platform.
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Combine automated and manual testing with CI/CD integration to catch issues early and deliver reliable React Native releases.
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Combine automated and manual testing with CI/CD integration to catch issues early and deliver reliable React Native releases.
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Design and validate React Native architectures that scale-supporting high traffic, modular teams, and long-term performance.
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