Szymon Chmal

Szymon Chmal

@chmal.it

Dev Lead / Senior React Native Developer x Callstack | Microsoft MVP | Speaker | GDG Toruń Leader

126 followers33 following96 posts

Szymon Chmal
@chmal.it

The Jest integration I sneak-peeked earlier is also letting me roll out code coverage support. The coverage reporter is already in place. I just had to instrument the code and send the coverage data from the device back to the CLI. Surprisingly, it was really easy to implement!

Szymon Chmal
@chmal.it

Harness isn't a simple tool - it's a bunch of components working together to give the best DX for testing JS code with native modules. Maintaining all that as a solo dev isn't easy, so I tried offloading some work by using Jest's CLI to run Harness… and it worked!

Szymon Chmal
@chmal.it

Expect it to be included in the next Harness release! With it, I can leverage Jest's infrastructure, such as built-in reporters, and potentially support running the same test suite in parallel across multiple devices. Huge thanks to @thymikee.bsky.social for pitching the idea at React Conf!

Szymon Chmal
@chmal.it

We're hosting a livestream today, with a special focus on React Native Harness! Expect insider insights on how it all works and sneak peeks at what's coming next. 🗓️ Thu 16, 5 PM CEST See you there!

Szymon Chmal
@chmal.it

🎉 Introducing React Native Harness - a lightweight framework for testing native modules directly on device or emulator. Write tests in a Jest-like syntax, run them in a real React Native runtime, and verify native behavior without mocks.

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Szymon Chmal
@chmal.it

🎉 Introducing React Native Harness - a lightweight framework for testing native modules directly on device or emulator. Write tests in a Jest-like syntax, run them in a real React Native runtime, and verify native behavior without mocks.

View full thread
Szymon Chmal
@chmal.it

Harness runs wherever Metro runs, starting with iOS and Android. It's built to be portable, making support for new platforms straightforward. As proof, we're also bringing support for VegaOS.

Szymon Chmal
@chmal.it

Designed for library authors and teams building native integrations. It is cross-platform, works on CI/CD and made to test real native behavior with a familiar workflow.

Szymon Chmal
@chmal.it

🎉 Introducing React Native Harness - a lightweight framework for testing native modules directly on device or emulator. Write tests in a Jest-like syntax, run them in a real React Native runtime, and verify native behavior without mocks.

Szymon Chmal
@chmal.it

Harness runs tests in a real React Native runtime. Unlike Jest, it doesn't rely on mocks and unlike Detox or Maestro, it focuses on testing native code directly, not automating UI flows.

Szymon Chmal
@chmal.it

Are you using the Performance API in React Native? If yes, I'm pretty sure you've wished a bunch of times that you could check out measures like you do in Chrome DevTools. What if I told you Rozenite is about to bring you that same vibe? Hot or not?

Szymon Chmal
@chmal.it

Yesterday, the community requested server-side event support for Rozenite's Network Activity. I said I'd look into it… but somehow ended up pushing a branch with the feature almost done. Whoops! 🙈

Szymon Chmal
@chmal.it

The Rozenite plugin family is growing, so I created a plugin directory! It includes both official plugins and community ones like rozenite-preview. Best part? You can add your own by opening a quick pull request on the Rozenite repo.

Szymon Chmal
@chmal.it

Just found out I'll be speaking at React Universe Conf! Rozenite's been out for a while, but in this talk, I'll dive deeper into how it works under the hood - how I hooked into DevTools without forking anything, and how you can build your own plugins too. Hope to see you there!

Szymon Chmal
@chmal.it

New week, new feature! Struggling to understand what's going on in your WebSocket connection? Fear not! Thanks to Rozenite, you'll soon be able to inspect WebSocket traffic and review each message one by one - whether it's text, binary, or JSON. Coming soon 🔥

Szymon Chmal
@chmal.it

Rozenite's Network Activity plugin got a major overhaul yesterday! The new UI and improved functionality make it much more convenient to use. You can now inspect request bodies and responses with an interactive JSON viewer 🚀

Szymon Chmal
@chmal.it

Next stop: WebSocket interception - just like Chrome DevTools! You'll be able to see every message going in and out of the device. What do you think - super useful or not really? 🤔

Szymon Chmal
@chmal.it

Rozenite is gaining traction - we've just crossed 50 stars on GitHub, and the number is steadily rising! It was included in the latest edition of the This Week in React newsletter, so if you slept through the release, it's high time you gave it a try and left a star while you're at it 🌟

Seb ⚛️ ThisWeekInReact.com@sebastienlorber.com

This Week In React 245 🍿 Read/subscribe here: thisweekinreact.com/newsletter/245 ⚛️ React: - TanStack - React Core - Next MCP - RSC - memo - Remix - Base UI - React Aria 📱 RN: - Precompiled iOS - Rozenite - AI - Perf - Nitro - BottomSheet - Tinybase

Szymon Chmal
@chmal.it

Redux DevTools plugin for Rozenite is nearly complete. It offers basic debugging functionality, though without time travel or action dispatch capabilities. There's an upstream issue with the package that needs to be addressed first. github.com/callstackinc...

github.comfeat: introduce Redux Devtools plugin by V3RON · Pull Request #5 · callstackincubator/rozeniteThis branch introduces a new Redux DevTools plugin for Rozenite, providing Redux state inspection and debugging capabilities within React Native DevTools. The plugin enables real-time state monitor...
Szymon Chmal
@chmal.it

Rozenite - a plugin framework for React Native DevTools - is now live in alpha! 🎉 What started as a hacky PoC is now something you can use in real projects. Still lots to come: better network monitor, Redux DevTools, Re.Pack support & more 💪

Szymon Chmal
@chmal.it

Big news: the React Native DevTools framework is dropping by the end of this month 🔥 The name? It's locked in and I'm so excited about it. It kicks off a whole family of tools designed to push React Native even further… but I'm not allowed to say anything else at this point 🙊

Szymon Chmal
@chmal.it

Just found out I'll be speaking at React Advanced! I'll be sharing my journey hacking on React Native Devtools + building a plugin framework from scratch. If you're curious how it all came together, tune in! The live stream is free - just register here: gitnation.com/badges/react...

gitnation.comCheck out my badge & claim your free React Advanced 2025 remote ticket!Join 5k engineers worldwide at React Advanced 2025 and meet 50+ top speakers at Nov 27 - Dec 1, 2025
Szymon Chmal
@chmal.it

Short RSC update: ✅ 'use client' and 'use server' now become proxies. ✅ Server rendering is... holding together with duct tape. Now to bundle client components and pray React Native accepts them 🙃

Szymon Chmal
@chmal.it

Might write a post (or a survival guide) about this RSC journey - from "how hard can it be?" to "send help." Would you be brave enough to read it? 😅

Szymon Chmal
@chmal.it

The sun’s out, the birds are singing... and I’m buried in last-minute tweaks to the playground app for today’s JavaScript Performance webinar 😅 Still time to grab a spot if you missed the announcement! 👇 streamyard.com/watch/pnM9CY...

streamyard.comMaster JavaScript Performance in React Native: Part 2This is Part 2 of our JavaScript optimization deep dive—a continuation of the webinar we hosted two weeks ago, based on Part 1 of Callstack’s Ultimate Guide to React Native Optimization. Hosted by: 🎙...
Szymon Chmal
@chmal.it

I'm gathering examples of situations where developers might choose popular tools or patterns without fully considering if they fit the project's needs. For instance, using SSR for dynamic dashboards where it's not really necessary. Got any ideas for similar examples? 🧐

Szymon Chmal
@chmal.it

Another hype cycle is starting. People are asking if they should learn Lynx, as it's being called a "React Native killer." It’s probably too early to say, but some influencers are already fueling the buzz for views and likes.

Szymon Chmal
@chmal.it

Lynx: a hit or a miss? Let's find out together. This is going to be fun 🔥

lukasz.app@lukasz.app

LynxJS: Fresh Take or Just a Copy-Paste? We’re going live this Friday, March 7th at 5:30 PM CET to check out LynxJS for the first time. Join me, @grabbou.com, @matthargett.bsky.social and @chmal.it as we test it out, live code, and share our thoughts. Where? 📺 www.youtube.com/watch?v=MCCy...

youtube.comLynxJS: First Impressions, Live Coding & What’s Under the HoodYouTube video by Callstack Engineers
Szymon Chmal
@chmal.it

Been exploring visual regression testing tools for React Native lately and it feels like the space is underdeveloped. 🤔 What features would your dream visual regression tool have to make you want to use it?

Szymon Chmal
@chmal.it

Anyone know how to capture and stream an iOS simulator’s screen? It used to be possible with simctl a few years ago. I tried idb, but the stream is full of artifacts 🤔

Szymon Chmal
@chmal.it

Just switched from Terser to SWC in Metro. Saw nearly a 30% improvement in build time and even a slight reduction in size. Worth it 🔥

Szymon Chmal
@chmal.it

Why did no one mention Synology NASes are this loud? My router is near my bedroom, and so is the NAS. Some nights, it’s noisy enough to pull me out of sleep ☹️

Szymon Chmal
@chmal.it

I just signed up for three runs this year: a 5km, a 10km, and, wait for it, a half marathon. I’m almost certain I’ll be questioning all my life choices the moment the starting whistle blows, lol

Szymon Chmal
@chmal.it

January’s barely started, but I think I’ve found my hack of the year! How to keep a Google Cast session alive when an iOS device locks? Normally, iOS kills network activity after about a minute. The solution? Loop a silent MP3 while the video plays. It sounds ridiculous, but hey - it works! 🚀