Jest Config Generator

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.