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⚠️ HIGH PRIORITY: Verify current Jest ecosystem to prevent outdated configuration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