Migrate Jest → Vitest

Vitest is largely Jest-API-compatible but runs faster (especially with Vite), supports ESM natively, and has better TS integration. Migration is mostly mechanical — the wins are in test speed and ESM compatibility.

When to use

• Just migrated to Vite (see webpack-to-vite) — Vitest is the matching test runner.
• Jest is slow on a large suite (> 30s).
• Jest's ESM support is fighting you.
• You want native TS support without Babel overhead.

When NOT to use

• React Native projects — Jest is the established choice; jest-expo specifically.
• Heavy Jest-only plugins with no equivalent (rare; check first).
• Brand-new codebase — start with Vitest directly.

API compatibility (high)