I care a lot about testing. I don’t know if that’s obvious yet, but hopefully it’s obvious. I wanted to trace the lineage of the testing tools we use today, because I think understanding where they came from helps you appreciate why things work the way they do.

Where It All Started

Automated testing as we know it really started with SUnit for the Smalltalk language. Kent Beck created it back in 1989, and it established the patterns that every test framework still borrows from today.

In 1997, Kent Beck and Erich Gamma ported those ideas to Java and created JUnit. JUnit was, or is, incredibly influential to pretty much every unit testing framework you’ve ever used. The test runner, assertions, setup and teardown, all of that traces back to JUnit.

But I’m going to focus on the JavaScript side of things here.

Jest: The Facebook Era

Jest was originally created at Facebook in 2011 as part of a major platform rewrite. It became the dominant testing framework for React and Node.js codebases, and in 2022, Facebook released it to the OpenJS Foundation.

Jest works well, but it carries some baggage. It requires a transpilation pipeline, something that was common a decade ago but feels burdensome now. If you want to use ESM modules, there’s an extra step involved. It’s adds friction.

So what else is there?

Vitest: The Modern Alternative

Vitest is a modern alternative, built on top of Vite. It supports ESM modules and TypeScript out of the box; so no transpilation step needed. And because Vite has HMR (hot module replacement), the watch mode for rerunning tests is very fast.

Vitest was initially created by Anthony Fu and the company behind Vue.js. The initial commit was in December 2021, so it’s a relatively recent project. They’ve made incredible progress since then.

Vitest uses Vite under the hood. So lets look at that briefly.

Why Vite Is So Fast

Vite’s speed comes from esbuild, which is written in Go. It compiles directly to native machine code, so it bypasses the JavaScript engine’s overhead entirely. It can transform TypeScript significantly faster because it doesn’t need to go through the JS engine. And because it’s Go, it’s multithreaded.

But things are changing. In Vite 8, the bundler is moving from esbuild to Rolldown. This is new tool written in Rust that combines the best of esbuild and Rollup.

Why? Currently, Vite uses esbuild during development but switches to Rollup for production builds. Two different tools for two different use cases. Rolldown unifies both into a single tool that handles dev and production.

What Did We Learn?

Hopefully something! How about a mini review to nail it home:

• 1989: SUnit (Smalltalk) — Kent Beck starts it all
• 1997: JUnit (Java) — the template everything else follows
• 2011: Jest — Facebook’s testing framework, now under OpenJS Foundation
• 2021: Vitest — modern, fast, ESM-native testing built on Vite
• Coming soon: Rolldown replaces esbuild + Rollup in Vite 8

That’s all for now!