Bun Jest Migration

Migrating from Jest to Bun's test runner is mostly painless since Bun maintains Jest compatibility, but there are a few gotchas around module mocking and timers. This guide walks you through removing Jest dependencies, updating imports from @jest/globals to bun:test, and translating the parts that differ (like jest.mock becoming mock.module and jest.fn becoming mock). The configuration section showing jest.config.js to bunfig.toml conversion is helpful, and the troubleshooting table catches the main pain points like mock hoisting not working the same way. If you're moving a test suite to Bun, this covers the practical stuff you'll actually hit.

skills.sh installs: 326
GitHub stars: 248
last updated: Aug 21, 2026

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Install

$ npx -y skills add secondsky/claude-skills --skill bun-jest-migration --agent claude-code

Installs into .claude/skills of the current project.

Files

Bun Jest Migration

Bun's test runner is Jest-compatible. Most Jest tests run without changes.

Quick Migration

# 1. Remove Jest dependencies
bun remove jest ts-jest @types/jest babel-jest

# 2. Update test script
# package.json: "test": "bun test"

# 3. Run tests
bun test

Import Changes

// Before (Jest)
import { describe, it, expect, jest } from '@jest/globals';

// After (Bun) - No import needed, or explicit:
import { describe, test, expect, mock, spyOn } from "bun:test";

API Compatibility

Fully Compatible

Jest	Bun	Notes
`describe()`	`describe()`	Identical
`it()` / `test()`	`test()`	Use `test()`
`expect()`	`expect()`	Same matchers
`beforeAll/Each`	`beforeAll/Each`	Identical
`afterAll/Each`	`afterAll/Each`	Identical
`jest.fn()`	`mock()`	Use `mock()`
`jest.spyOn()`	`spyOn()`	Identical