Can I still use fake timers in Bun?

Yes, Bun supports Jest-compatible timer APIs. You can import setSystemTime and jest from bun:test to manage time-based tests effectively.

Is Bun's test runner fully compatible with Jest?

Bun's test runner is designed for high compatibility, supporting most Jest matchers, snapshots, and lifecycle hooks natively, though some API names like jest.mock() change to mock.module().

How do I handle module mocking in Bun compared to Jest?

Bun uses mock.module() instead of jest.mock(). Because Bun does not use Jest's hoisting mechanism, you should define your mocks before your imports or use dynamic imports.

What happens to my snapshots during migration?

Snapshots are generally compatible. If there are minor serialization differences, you can update them easily by running 'bun test --update-snapshots'.

Bun Jest Migration

Name: Bun Jest Migration
Author: secondsky

bysecondsky

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Security & Testing

Migrates existing Jest test suites to Bun's high-performance test runner with automated configuration and code conversion guidance.

This skill provides comprehensive guidance and automated patterns for transitioning from Jest to Bun's native test runner. It streamlines the migration process by mapping Jest APIs to Bun equivalents, converting configuration files from JavaScript to TOML, and resolving common hurdles like module mocking and timer implementation. It is essential for developers looking to leverage Bun's superior execution speed while maintaining the familiarity and reliability of Jest-compatible testing structures.

Key Features

01Seamless conversion of jest.config.js settings to bunfig.toml

02Troubleshooting support for snapshot mismatches and hoisting issues

0321 GitHub stars

04Automated dependency cleanup and package script updates

05Advanced guidance for complex module mocking and timer migrations

06Direct mapping of Jest globals and matchers to Bun's native testing API

Use Cases

01Optimizing CI/CD pipelines by migrating to Bun's significantly faster test execution engine

02Standardizing testing workflows in Bun-native monorepos using native tooling

03Converting a legacy Node.js/Jest project to a modern, high-speed Bun-based stack

What are Skills?·How to Install

Install with 🐟 Skill.Fish

npx skillfish add secondsky/claude-skills bun-jest-migration

For use in Claude.ai and ChatGPT

Download Skill