---
title: "Write Once, Test Everywhere: Cross-Platform Testing for React Native"
description: "Join Szymon Chmal at WarsawJS #133 to explore cross-platform testing in React Native with a new approach powered by React Native Harness."
url: https://www.callstack.com/events/write-once-test-everywhere-cross-platform-testing-for-react-native-2
updated: 2026-10-24T08:39:22.948Z
---

# Write Once, Test Everywhere: Cross-Platform Testing for React Native

Join Szymon Chmal at WarsawJS #133 to explore cross-platform testing in React Native with a new approach powered by React Native Harness.

_Talk · 12/9/2025, 7PM [CET] · Warsaw, Poland · Category: Testing_

Organizer: WarsawJS Meetup

Speakers: Szymon Chmal (Software Developer @ Callstack)

[Event page](https://warsawjs.com/)

Testing React Native apps has always been a trade-off between speed and realism. Jest is fast, familiar, and excellent for unit tests, but it runs in Node.js and relies on mocks for native modules. End-to-end frameworks offer realism, but at the cost of complex setup, ongoing maintenance, and slower pipelines. Enter React Native Harness, a new testing framework that lets you run Jest-style tests directly on real devices and simulators, with full access to native modules and no mocks by default.