Vitest Has a Free API — The Fastest Unit Testing Framework

Vitest is the blazing fast unit test framework powered by Vite — it's Jest-compatible, runs ESM natively, and is 2-10x faster. Completely free. Why Vitest Over Jest? Vite-powered — uses Vite's transform pipeline, instant HMR for tests Jest-compatible — same API ( describe , it , expect ), easy migration ESM native — no more babel-jest or ts-jest configs In-source testing — write tests next to your code Browser mode — run tests in real browsers UI dashboard — visual test explorer Quick Start npm install -D vitest // package.json { "scripts" : { "test" : "vitest" , "test:ui" : "vitest --ui" , "test:coverage" : "vitest run --coverage" } } Writing Tests // math.test.ts import { describe , it , expect } from " vitest " ; import { add , multiply , divide } from " ./math " ; describe ( " Math utilities " , () => { it ( " adds two numbers " , () => { expect ( add ( 2 , 3 )). toBe ( 5 ); expect ( add ( - 1 , 1 )). toBe ( 0 ); }); it ( " multiplies two numbers " , () => { expect ( multiply ( 3 ,