Bun test vs Vitest: Speed vs Vite-Native Testing
Bun test is the very fast runner built into the Bun runtime; Vitest is a Vite-native, Jest-compatible framework with a rich feature set.
Bun test is built into Bun, offering extremely fast startup and a Jest-like API with no separate install when you use Bun. Vitest is a Vite-powered test framework with a Jest-compatible API, ESM-first design, watch mode, and tight integration with Vite-based projects, running on Node.
| Bun test | Vitest | |
|---|---|---|
| Runtime | Bun (built in) | Node (Vite-powered) |
| Speed | Very fast | Fast |
| API | Jest-like | Jest-compatible |
| Vite integration | No | Native |
| Best for | Bun projects, raw speed | Vite apps, rich features |
In CI
Bun test is compelling when you already use Bun and want the fastest possible test runs with minimal tooling. Vitest is the natural choice for Vite-based apps - shared config, transforms, and a mature, Jest-compatible feature set. If you are on Vite, Vitest fits seamlessly; if you are on Bun and want speed, Bun test is hard to beat. Check feature parity before migrating a large suite.
Speed it up
Cache dependencies keyed on your lockfile so tests start warm. Tests run on CI runners; faster managed runners shorten the test step.
The switching cost is mostly in the parts nobody lists
- Assertions and mocks usually port mechanically when the target implements a compatible API; custom transformers and framework plugins do not.
- Snapshot formats differ between runners, so plan to regenerate and review rather than port.
- Run both suites in parallel in CI for a period and diff the results. A migration that changes which tests fail is not a migration, it is a regression you have not found yet.
- Coverage numbers move on a runner change even when the tests do not, because instrumentation differs. Re-baseline any coverage gate deliberately.
The verdict
Already on Bun and want maximum speed: Bun test. On a Vite-based app wanting native integration and rich features: Vitest. Both are fast and Jest-like - pick by your runtime and build tool.