Jest Config Skill

Purpose

Generate the

jest.config.cjs

file for unit testing configuration with Jest.

⚠️ CONDITIONAL EXECUTION

This skill should ONLY be used if the project uses Jest instead of Vitest.

Test Framework Detection:

1. Check

   package.json

   for test framework dependency:
   • If

     "vitest"

     found → SKIP THIS SKILL (use vitest-config skill instead)
   • If

     "jest"

     found → EXECUTE THIS SKILL
   • If neither found → PROMPT USER: "Which test framework do you want to use: Jest or Vitest?"

Note: Vitest is the officially recommended test framework for Vue 3 projects as of 2024+. Jest is considered legacy but still widely used.

🚨 MANDATORY FILE COUNT

This skill MUST create exactly 1 file:

• jest.config.cjs

  (preferred format - CommonJS)

🔍 BEFORE GENERATING - CRITICAL RESEARCH REQUIRED

⚠️ HIGH PRIORITY: Verify current Jest ecosystem to prevent outdated configuration

Required Research Steps:

1. Jest Version: Check current Jest version and configuration format
   • Verify Jest is still maintained and supported
   • Check if

     jest.config.cjs

     format is still recommended
2. Vue 3 Jest Transformer: CRITICAL - Check if

   @vue/vue3-jest

   is still maintained
   • Run:

     npm view @vue/vue3-jest time

   • Check last publish date and maintenance status
   • If deprecated or unmaintained:
     • STOP and PROMPT USER: "@vue/vue3-jest appears unmaintained. Vitest is now recommended for Vue 3. Should we continue with Jest or switch to Vitest?"
     • Wait for user decision before proceeding
   • If maintained: Verify current version and compatibility with Jest 29+
3. Coverage Provider: Verify

   v8

   vs

   babel

   coverage provider
   • Check if

     v8

     is still recommended over

     babel

   • Verify compatibility with current Jest version
   • Check performance and accuracy differences
4. TypeScript Support: Verify

   ts-jest

   transformer
   • Check if

     ts-jest

     is still maintained
   • Verify compatibility with TypeScript and Jest versions
5. ESM Package Detection: Identify packages requiring transformation
   • Check

     package.json

     for ESM-only packages (axios, date-fns, etc.)
   • Research which packages need to be in

     transformIgnorePatterns

   • Common ESM packages: axios, lodash-es, uuid (verify current list)
6. Test Environment: Verify

   jsdom

   is still recommended
   • Check if

     jsdom

     or

     node

     environment is appropriate
   • Verify

     jsdom

     version compatibility
7. File Format Options: Check if format is deprecated
   • Verify

     .cjs

     format is still preferred
   • Check

     .js

     ,

     .mjs

     ,

     .json

     , package.json field alternatives

Output

Create the file:

jest.config.cjs

Supported Format:

• jest.config.cjs

  (strict preferred format - CommonJS, most compatible)

Alternative Formats (only if .cjs deprecated):

• jest.config.js

  (JavaScript, follows package.json type)

• jest.config.mjs

  (ES Module format)

• jest.config.json

  (JSON format, limited functionality)

Example File

See:

examples.md

in this directory for complete examples and detailed explanations.

⚠️ IMPORTANT: The examples.md file contains December 2025 configurations. Always verify current Jest ecosystem before using.

Execution Checklist

• Detect test framework from package.json (Jest vs Vitest)
• If Vitest detected, skip this skill entirely
• If Jest detected, proceed with research
• Research current Jest version and configuration format
• CRITICAL: Verify

  @vue/vue3-jest

  maintenance status
• If

  @vue/vue3-jest

  unmaintained, prompt user for decision
• Verify

  ts-jest

  transformer compatibility
• Research coverage provider (

  v8

  vs

  babel

  )
• Detect ESM packages in package.json needing transformation
• Verify

  jsdom

  test environment compatibility
• Create

  jest.config.cjs

  with current standards
• Verify file format is still recommended (not deprecated)

🛑 BLOCKING VALIDATION CHECKPOINT

STOP! Before proceeding to the next skill, verify:

Automated Verification

Run this command to verify the file exists:

if [ -f "jest.config.cjs" ] || [ -f "jest.config.js" ] || [ -f "jest.config.mjs" ] || grep -q "\"jest\":" package.json 2>/dev/null; then
  echo "✓ Jest configuration found"
  if [ -f "jest.config.cjs" ]; then
    echo "✓ Using jest.config.cjs (preferred format)"
  fi
  
  # Check for Vitest conflict
  if grep -q "\"vitest\"" package.json 2>/dev/null; then
    echo "⚠ WARNING: Both Jest and Vitest detected in package.json"
    echo "  Consider using only one test framework"
  fi
else
  echo "✗ Jest configuration missing"
  exit 1
fi

Manual Verification

1. ✓

   jest.config.cjs

   exists at project root
2. ✓ File uses CommonJS format (

   module.exports

   )
3. ✓ File includes

   preset: 'ts-jest'

   for TypeScript support
4. ✓ File includes

   testEnvironment: 'jsdom'

   for DOM testing
5. ✓ File includes Vue transformer (

   @vue/vue3-jest

   - if maintained)
6. ✓

   transformIgnorePatterns

   includes detected ESM packages
7. ✓ Coverage provider is set (verify

   v8

   or

   babel

   )
8. ✓ Module name mapper includes path aliases (

   @/

   →

   src/

   )
9. ✓ No Vitest configuration conflict in package.json

If Validation Fails

DO NOT PROCEED to the next skill. Create or fix the missing/incorrect file immediately.

Notes

• Conditional Execution: Only use if project uses Jest (not Vitest)
• Vitest Preferred: For new Vue 3 projects, Vitest is officially recommended
• Coverage Provider:

  v8

  is faster and more accurate than

  babel

  (verify current recommendation)
• Vue Transformer:

  @vue/vue3-jest

  transforms Vue SFC files (check maintenance status)
• TypeScript Support:

  ts-jest

  transforms TypeScript files
• ESM Handling:

  transformIgnorePatterns

  allows testing ESM packages
• Coverage Exclusions: Excludes infrastructure files (main.ts, router, services, etc.)
• Module Name Mapper: Handles

  @/

  path aliases and asset imports
• Test Environment:

  jsdom

  provides DOM APIs for component testing
• Setup Files: Can configure test environment and globals
• Always verify current ecosystem - Jest/Vue testing landscape evolves
• CommonJS Format:

  .cjs

  ensures compatibility with all module systems
• Legacy Status: Jest is legacy for Vue 3; consider migrating to Vitest