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name: jest-config description: Generates jest.config.cjs for unit testing configuration. Configures Jest with Vue, TypeScript support, coverage thresholds, and test environment settings.

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⚠️ HIGH PRIORITY: Verify current Jest ecosystem to prevent outdated configuration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