If you've ever felt that running your tests is like waiting for water to boil, you're not alone. In my latest project, ilamy Calendar, I tried keeping a single toolchain for everything: runtime, package manager, and testing, and that led me to try Bun's built-in test runner.
The result surprised me: I wrote tests, ran them, and saw the results instantly, in milliseconds. I had used Jest and Vitest before; Jest in particular always seemed slow to me, slow enough to get up and grab a coffee while the suite finished. To really check how much faster Bun was, I did a small experiment.
I set up Jest, Vitest, and Bun test on the same project and ran the same 223 tests spread across 14 files, repeating each runner 10 times without changing the code, only swapping the runner.
These are the average times of the ten runs:
Bun Test approximately 2.15s
Vitest approximately 5.3s
Jest approximately 9.8s
Observed range per run: Jest between 9.3s and 12.6s, Vitest between 5.13s and 5.93s, Bun Test between 2.13s and 2.21s. The speed difference is so significant that even small projects notice the improvement, and when scaling to hundreds or thousands of tests, the time saved becomes massive.
If you want to try it live, I prepared a demo where you can run tests with Jest, Vitest, and Bun side by side and see the difference: https://dzpx7j-5173.csb.app/ and the source code is at https://codesandbox.io/p/devbox/tender-wescoff-dzpx7j
How to migrate to Bun Test in two simple steps: install Bun with the command curl -fsSL https://bun.sh/install | bash and then run your tests with bun test. Most Jest-style tests work without changes; if you use custom mocks, setup files, or advanced Jest features, you may need small adjustments, but Bun's compatibility is improving quickly.
My conclusions: I expected Bun to be fast, I didn't expect it to be this fast. If you value developer productivity, fast feedback cycles, and less time staring at spinners, it's worth trying Bun's test runner. It could make other runners a less attractive option.
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