Testing JavaScript by Kent C. Dodds: An Honest Review

What is Testing JavaScript?

Testing JavaScript is an online course by Kent C. Dodds — author of React Testing Library — that teaches how to efficiently test a JavaScript application using the Testing Trophy method. It's beginner-friendly on the testing side but assumes you've built a few web apps before. Eight modules, each packed with video lessons.

The core promise: learn the smart, efficient way to test any JavaScript application — without the dogma.

Why I took the course

As a software craftsman, testing is non-negotiable to me — it's what makes the difference between code I ship with confidence and code I'm scared to touch six months later. I had used Enzyme on previous projects, but the React community had clearly moved on to React Testing Library and its more user-centric philosophy. Learning testing directly from the library's author seemed like the most direct path to leveling up.

Did it deliver on its promise?

Yes — and for two distinct audiences.

If you're new to the JavaScript testing ecosystem, the course gives you a coherent mental model and saves you months of trial-and-error. If you're a veteran, you'll still pick up sharper patterns and a clearer rationale for the trade-offs you already make intuitively. Check the modules on the landing page and judge whether the investment fits your stage.

In my case I had testing experience, but I still walked away with a stronger foundation — patterns I now apply to every personal and professional project, and that I've taught to the engineers I work with.

From course to production: a real story

A few years ago I joined a client who had just raised a serious round and was scaling fast. Their stack had solid E2E coverage but almost no frontend unit or integration tests. As the codebase grew, E2E alone became a bottleneck — too slow, too coarse, blind to the edge cases that actually broke things in production.

Convincing leadership to invest in a proper frontend testing layer is rarely easy. We pushed, and they eventually gave us a window. The team knew I had completed Testing JavaScript and asked me to lead the effort — pick the tools, set the patterns, integrate them into the existing codebase, and bring the frontend teams along.

I took it. Step by step we shipped a real test infrastructure, added tests to the definition of done for every task, and shifted the team culture toward something closer to a test-driven mindset. Code quality went up. Regressions went down. The amount of time spent debugging in production dropped meaningfully. And — almost more importantly — engineers started taking pride in shipping things they trusted.

I became the go-to person for frontend testing in that org. Beyond fulfilling its promise, the course opened opportunities that I'm still benefiting from today.

Worth it?

If you write JavaScript for a living, yes — without hesitation. The course pays for itself the first time it stops you from shipping a regression.