bun test 1.4.2 vs Vitest 5.0.3 on 300 TypeScript tests in 60 files: warm wall medians 136 ms vs 1,673 ms (~12x); Vitest --no-isolate 765 ms (~5.6x). A 5-file vitest-API check (vi.fn, vi.mock, fake timers, spyOn, it.each, snapshot) passed 7/7 under Bun.
Jest 30.5.2 vs Vitest 5.0.3 on 40 files / 200 Node tests: wall medians Jest 2027 ms, Vitest isolate-on 2422 ms, Vitest --no-isolate 1287 ms, Jest --runInBand 3346 ms. Both 200/200 pass. Leave Jest after measuring isolate; default isolate can lose.
Vitest 5 upgrade decision with ShopperCove timing: 20-file forks suite median ~512 ms on 5.0.3 vs ~547 ms on 4.1.10 (Node 22.20.0). Engines require Node 22.12+ and Vite 6.4+. clearMocks defaults true. No affiliate.