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ConfigsApr 12, 2026·2 min de lecture

Jest — Delightful JavaScript Testing Framework

Jest is a delightful JavaScript testing framework with a focus on simplicity. Zero-config for most JS/TS projects, snapshot testing, mocking, code coverage, and parallel test execution. Created by Facebook and used to test React, Instagram, and many large codebases.

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Introduction

Jest is a delightful JavaScript testing framework created by Facebook (now Meta). Zero-config for most React and TypeScript projects. Features include snapshot testing, built-in mocking, code coverage, parallel execution, and an intuitive API. Used to test React, Instagram, and many Meta properties.

What Jest Does

  • Zero-config — works out of the box for most JS/TS projects
  • Snapshot testing — capture and compare UI output
  • Mocking — jest.fn(), jest.mock(), jest.spyOn()
  • Code coverage — built-in Istanbul coverage
  • Parallel execution — tests run in isolated workers
  • Watch mode — re-run changed tests
  • Matchers — rich assertion library (toBe, toEqual, toThrow, toMatchSnapshot)
  • Timer mocks — fake timers for setTimeout/setInterval
  • Async testing — async/await, promises, callbacks

Comparison

Runner Speed TS ESM Watch
Jest Medium Via ts-jest Experimental Yes
Vitest Fast Native Native Yes
Mocha Medium Via ts-node Yes Yes
Node test runner Fast Via tsx Yes Yes

FAQ

Q: Jest vs Vitest? A: Vitest is faster (Vite-powered), native ESM, and TS works without ts-jest. Vitest is recommended for new Vite projects. Jest has a larger ecosystem and more legacy projects.

Q: How to configure TypeScript? A: Use the ts-jest transformer or @swc/jest (faster). Configure the transform field in jest.config.ts.

Sources

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