name: jest-config-generator description: Generate Jest configuration files for JavaScript/TypeScript testing with coverage, mocking, and environment-specific settings. Triggers on "create jest config", "generate jest.config", "jest configuration for", "testing config".

Jest Config Generator

Generate optimized Jest configuration files for JavaScript and TypeScript testing projects.

Output Requirements

File Output: jest.config.js, jest.config.ts, or jest.config.json Format: JavaScript module (ESM or CJS) or JSON Compatibility: Jest 29.x

When Invoked

Immediately generate a complete Jest configuration appropriate for the project type. Include sensible defaults for coverage, transforms, and module resolution.

Configuration Templates

TypeScript Project (Node.js)

// jest.config.js
/** @type {import('jest').Config} */
const config = {
  // Test environment
  testEnvironment: 'node',

  // File extensions
  moduleFileExtensions: ['ts', 'tsx', 'js', 'jsx', 'json'],

  // Transform TypeScript files
  transform: {
    '^.+\\.tsx?$': [
      'ts-jest',
      {
        tsconfig: 'tsconfig.json',
        isolatedModules: true,
      },
    ],
  },

  // Test file patterns
  testMatch: [
    '**/__tests__/**/*.+(ts|tsx|js)',
    '**/?(*.)+(spec|test).+(ts|tsx|js)',
  ],

  // Ignore patterns
  testPathIgnorePatterns: [
    '/node_modules/',
    '/dist/',
    '/build/',
  ],

  // Module path aliases (match tsconfig paths)
  moduleNameMapper: {
    '^@/(.*)$': '<rootDir>/src/$1',
    '^@utils/(.*)$': '<rootDir>/src/utils/$1',
    '^@models/(.*)$': '<rootDir>/src/models/$1',
  },

  // Setup files
  setupFilesAfterEnv: ['<rootDir>/jest.setup.ts'],

  // Coverage configuration
  collectCoverageFrom: [
    'src/**/*.{ts,tsx}',
    '!src/**/*.d.ts',
    '!src/**/index.ts',
    '!src/**/*.stories.{ts,tsx}',
    '!src/types/**/*',
  ],
  coverageDirectory: 'coverage',
  coverageReporters: ['text', 'lcov', 'html'],
  coverageThreshold: {
    global: {
      branches: 80,
      functions: 80,
      lines: 80,
      statements: 80,
    },
  },

  // Performance
  maxWorkers: '50%',
  cache: true,
  cacheDirectory: '<rootDir>/.jest-cache',

  // Timeouts
  testTimeout: 10000,

  // Clear mocks between tests
  clearMocks: true,
  restoreMocks: true,

  // Verbose output
  verbose: true,
};

module.exports = config;

React Application (Vite/CRA)

// jest.config.js
/** @type {import('jest').Config} */
const config = {
  // Use jsdom for DOM testing
  testEnvironment: 'jsdom',

  // Setup files
  setupFilesAfterEnv: ['<rootDir>/src/setupTests.ts'],

  // Transform
  transform: {
    '^.+\\.(ts|tsx)$': [
      'ts-jest',
      {
        tsconfig: 'tsconfig.json',
        isolatedModules: true,
      },
    ],
    '^.+\\.(js|jsx)$': 'babel-jest',
  },

  // Module resolution
  moduleNameMapper: {
    // Handle CSS imports
    '\\.(css|less|scss|sass)$': 'identity-obj-proxy',

    // Handle image imports
    '\\.(jpg|jpeg|png|gif|svg|webp)$': '<rootDir>/__mocks__/fileMock.js',

    // Path aliases
    '^@/(.*)$': '<rootDir>/src/$1',
    '^@components/(.*)$': '<rootDir>/src/components/$1',
    '^@hooks/(.*)$': '<rootDir>/src/hooks/$1',
    '^@utils/(.*)$': '<rootDir>/src/utils/$1',
  },

  // Test patterns
  testMatch: [
    '<rootDir>/src/**/__tests__/**/*.{ts,tsx}',
    '<rootDir>/src/**/*.{spec,test}.{ts,tsx}',
  ],

  // Ignore
  testPathIgnorePatterns: [
    '/node_modules/',
    '/dist/',
    '/.next/',
  ],

  // Transform ignore
  transformIgnorePatterns: [
    '/node_modules/(?!(uuid|other-esm-package)/)',
  ],

  // Coverage
  collectCoverageFrom: [
    'src/**/*.{ts,tsx}',
    '!src/**/*.d.ts',
    '!src/**/*.stories.{ts,tsx}',
    '!src/main.tsx',
    '!src/vite-env.d.ts',
  ],
  coverageDirectory: 'coverage',
  coverageReporters: ['text', 'lcov', 'html'],

  // Mock behavior
  clearMocks: true,
  restoreMocks: true,

  // Globals
  globals: {
    'ts-jest': {
      isolatedModules: true,
    },
  },
};

module.exports = config;

Next.js Application

// jest.config.js
const nextJest = require('next/jest');

const createJestConfig = nextJest({
  // Path to Next.js app
  dir: './',
});

/** @type {import('jest').Config} */
const customConfig = {
  // Test environment
  testEnvironment: 'jest-environment-jsdom',

  // Setup files
  setupFilesAfterEnv: ['<rootDir>/jest.setup.ts'],

  // Module aliases (synced with tsconfig.json)
  moduleNameMapper: {
    '^@/(.*)$': '<rootDir>/src/$1',
    '^@components/(.*)$': '<rootDir>/src/components/$1',
    '^@lib/(.*)$': '<rootDir>/src/lib/$1',
    '^@hooks/(.*)$': '<rootDir>/src/hooks/$1',
  },

  // Test patterns
  testMatch: [
    '**/__tests__/**/*.[jt]s?(x)',
    '**/?(*.)+(spec|test).[jt]s?(x)',
  ],

  // Ignore
  testPathIgnorePatterns: [
    '<rootDir>/node_modules/',
    '<rootDir>/.next/',
    '<rootDir>/e2e/',
  ],

  // Coverage
  collectCoverageFrom: [
    'src/**/*.{js,jsx,ts,tsx}',
    '!src/**/*.d.ts',
    '!src/**/*.stories.{js,jsx,ts,tsx}',
    '!src/app/layout.tsx',
    '!src/app/providers.tsx',
  ],

  // Module directories
  moduleDirectories: ['node_modules', '<rootDir>/'],
};

module.exports = createJestConfig(customConfig);

API/Backend (Express/Fastify)

// jest.config.js
/** @type {import('jest').Config} */
const config = {
  preset: 'ts-jest',
  testEnvironment: 'node',

  // Root directory
  roots: ['<rootDir>/src', '<rootDir>/tests'],

  // Transform
  transform: {
    '^.+\\.ts$': ['ts-jest', { tsconfig: 'tsconfig.json' }],
  },

  // Test patterns
  testMatch: [
    '**/tests/**/*.test.ts',
    '**/tests/**/*.spec.ts',
    '**/__tests__/**/*.ts',
  ],

  // Path mapping
  moduleNameMapper: {
    '^@/(.*)$': '<rootDir>/src/$1',
    '^@controllers/(.*)$': '<rootDir>/src/controllers/$1',
    '^@models/(.*)$': '<rootDir>/src/models/$1',
    '^@services/(.*)$': '<rootDir>/src/services/$1',
    '^@middleware/(.*)$': '<rootDir>/src/middleware/$1',
    '^@utils/(.*)$': '<rootDir>/src/utils/$1',
  },

  // Setup
  setupFilesAfterEnv: ['<rootDir>/tests/setup.ts'],
  globalSetup: '<rootDir>/tests/globalSetup.ts',
  globalTeardown: '<rootDir>/tests/globalTeardown.ts',

  // Coverage
  collectCoverageFrom: [
    'src/**/*.ts',
    '!src/**/*.d.ts',
    '!src/index.ts',
    '!src/types/**/*',
    '!src/migrations/**/*',
  ],
  coverageThreshold: {
    global: {
      branches: 70,
      functions: 80,
      lines: 80,
      statements: 80,
    },
  },

  // Test isolation
  clearMocks: true,
  restoreMocks: true,
  resetModules: true,

  // Timeouts (longer for integration tests)
  testTimeout: 30000,

  // Force exit after tests complete
  forceExit: true,
  detectOpenHandles: true,

  // Verbose
  verbose: true,
};

module.exports = config;

Monorepo (with projects)

// jest.config.js (root)
/** @type {import('jest').Config} */
const config = {
  // Use projects for monorepo
  projects: [
    '<rootDir>/packages/*/jest.config.js',
    '<rootDir>/apps/*/jest.config.js',
  ],

  // Root coverage
  collectCoverage: true,
  coverageDirectory: '<rootDir>/coverage',
  coverageReporters: ['text', 'lcov', 'json-summary'],

  // Merge coverage from all projects
  collectCoverageFrom: [
    'packages/*/src/**/*.{ts,tsx}',
    'apps/*/src/**/*.{ts,tsx}',
    '!**/*.d.ts',
    '!**/node_modules/**',
  ],
};

module.exports = config;

Package Project Example

// packages/shared/jest.config.js
/** @type {import('jest').Config} */
const config = {
  displayName: 'shared',
  preset: 'ts-jest',
  testEnvironment: 'node',

  rootDir: '.',

  testMatch: ['<rootDir>/src/**/*.test.ts'],

  moduleNameMapper: {
    '^@shared/(.*)$': '<rootDir>/src/$1',
  },

  // Use root tsconfig
  transform: {
    '^.+\\.tsx?$': [
      'ts-jest',
      { tsconfig: '<rootDir>/tsconfig.json' },
    ],
  },
};

module.exports = config;

Setup Files

jest.setup.ts (React)

// jest.setup.ts
import '@testing-library/jest-dom';

// Mock IntersectionObserver
global.IntersectionObserver = class IntersectionObserver {
  constructor() {}
  observe() { return null; }
  unobserve() { return null; }
  disconnect() { return null; }
} as any;

// Mock ResizeObserver
global.ResizeObserver = class ResizeObserver {
  constructor() {}
  observe() { return null; }
  unobserve() { return null; }
  disconnect() { return null; }
} as any;

// Mock matchMedia
Object.defineProperty(window, 'matchMedia', {
  writable: true,
  value: jest.fn().mockImplementation(query => ({
    matches: false,
    media: query,
    onchange: null,
    addListener: jest.fn(),
    removeListener: jest.fn(),
    addEventListener: jest.fn(),
    removeEventListener: jest.fn(),
    dispatchEvent: jest.fn(),
  })),
});

jest.setup.ts (API)

// tests/setup.ts
import { prisma } from '@/lib/prisma';

// Clean up after each test
afterEach(async () => {
  jest.clearAllMocks();
});

// Close database connection after all tests
afterAll(async () => {
  await prisma.$disconnect();
});

Mock Files

fileMock.js

// __mocks__/fileMock.js
module.exports = 'test-file-stub';

styleMock.js

// __mocks__/styleMock.js
module.exports = {};

Validation Checklist

Before outputting, verify:

Correct testEnvironment (node vs jsdom)
Transform matches file types used
Path aliases match tsconfig
Coverage excludes appropriate files
Setup files exist or noted as needed
ESM packages in transformIgnorePatterns
Appropriate timeouts set

Example Invocations

Prompt: "Create Jest config for a TypeScript Node.js API" Output: Complete jest.config.js with ts-jest, coverage, path aliases.

Prompt: "Generate Jest configuration for React Testing Library" Output: Complete jest.config.js with jsdom, RTL setup, CSS mocks.

Prompt: "Jest config for Next.js 14 with App Router" Output: Complete jest.config.js using next/jest with proper setup.

jest-config-generator

$ Installer