Jest to Vitest codemod

@kamaalio/jest-to-vitest-codemod is a comprehensive collection of codemods to help migrate from Jest to Vitest. It automatically transforms Jest APIs, imports, types, and project configuration to Vitest equivalents.

• Jest to Vitest codemod
  • Features
    • Jest API to Vitest API
    • Hook Transformations
    • Type Transformations
    • Import Management
    • Project Configuration
  • Requirements
  • Installation
  • Usage
    • Basic String Transformation
    • CLI
    • Advanced Usage with Codemod Framework
    • File Processing with Filename Context
  • Before/After Examples
    • Complex Jest Test File
  • API Reference
    • Default Export
    • Named Exports
  • Behavior and Limitations
  • Development
    • Running Tests
    • Building
    • Code Quality
  • Contributing
    • Development Setup
  • License

Features

This codemod performs the following transformations:

Jest API to Vitest API

• jest.mock() → vi.mock() (with proper async handling for requireActual)
• jest.spyOn() → vi.spyOn()
• jest.requireActual() → await vi.importActual() (automatically wraps functions as async)
• jest.setTimeout() → vi.setTimeout({ testTimeout: ... })
• jest.clearAllMocks() → vi.clearAllMocks()
• jest.resetAllMocks() → vi.resetAllMocks()
• jest.restoreAllMocks() → vi.restoreAllMocks()
• jest.useFakeTimers() → vi.useFakeTimers()
• jest.useRealTimers() → vi.useRealTimers()

Hook Transformations

• Converts single-expression hooks to block statements for Vitest compatibility
• beforeEach(() => setup()) → beforeEach(() => { setup() })

Type Transformations

• jest.Mock<T> → Mock<T>
• vi.Mock<T> → Mock<T>

Import Management

• Removes @jest/globals imports
• Automatically adds appropriate Vitest imports (describe, it, expect, vi, etc.)
• Handles both type and value imports correctly
• Optimizes import statements by combining related imports

Project Configuration

• Creates vitest.config.ts if it doesn't exist
• Updates package.json dependencies (removes Jest deps, adds Vitest)
• Removes Jest configuration files

Requirements

• Node.js ≥ 22.0.0
• TypeScript files (currently supports TypeScript syntax)

Installation

npm install @kamaalio/jest-to-vitest-codemod

Or using pnpm:

pnpm add @kamaalio/jest-to-vitest-codemod

Usage

Basic String Transformation

import jestToVitest from '@kamaalio/jest-to-vitest-codemod';

const jestCode = `
  import { describe, it, expect } from '@jest/globals';
  
  jest.mock('fs');
  
  describe('my test', () => {
    beforeEach(() => setup());
    
    it('should work', () => {
      const spy = jest.spyOn(console, 'log');
      expect(true).toBe(true);
      jest.clearAllMocks();
    });
  });
`;

const vitestCode = await jestToVitest(jestCode);
console.log(vitestCode);

Output:

import { beforeEach, describe, expect, it, vi } from 'vitest';

vi.mock('fs');

describe('my test', () => {
  beforeEach(() => {
    setup();
  });

  it('should work', () => {
    const spy = vi.spyOn(console, 'log');
    expect(true).toBe(true);
    vi.clearAllMocks();
  });
});

CLI

Run the codemod over a directory directly from the command line:

npx jest-to-vitest-codemod ./src

Advanced Usage with Codemod Framework

import { JEST_TO_VITEST_CODEMOD, JEST_TO_VITEST_LANGUAGE } from '@kamaalio/jest-to-vitest-codemod';

// Use with @kamaalio/codemod-kit or similar frameworks
const codemod = JEST_TO_VITEST_CODEMOD;

File Processing with Filename Context

import jestToVitest from '@kamaalio/jest-to-vitest-codemod';
import { parseAsync } from '@ast-grep/napi';
import { JEST_TO_VITEST_LANGUAGE } from '@kamaalio/jest-to-vitest-codemod';

const fileContent = await fs.readFile('test.spec.ts', 'utf-8');
const ast = await parseAsync(JEST_TO_VITEST_LANGUAGE, fileContent);
const result = await jestToVitest(ast, 'test.spec.ts');

Before/After Examples

Complex Jest Test File

Before:

import { describe, it, expect, beforeEach } from '@jest/globals';

jest.mock('./utils', () => ({
  ...jest.requireActual('./utils'),
  helper: jest.fn(),
}));

describe('Component', () => {
  let mockFn: jest.Mock<(x: number) => string>;

  beforeEach(() => jest.clearAllMocks());

  it('should handle mocks', () => {
    const spy = jest.spyOn(console, 'log');
    jest.setTimeout(10000);
    expect(true).toBe(true);
  });
});

After:

import { beforeEach, describe, expect, it, vi, type Mock } from 'vitest';

vi.mock('./utils', async () => ({
  default: {
    ...(await vi.importActual('./utils')),
    helper: vi.fn(),
  },
}));

describe('Component', () => {
  let mockFn: Mock<(x: number) => string>;

  beforeEach(() => {
    vi.clearAllMocks();
  });

  it('should handle mocks', () => {
    const spy = vi.spyOn(console, 'log');
    vi.setTimeout({ testTimeout: 10000 });
    expect(true).toBe(true);
  });
});

API Reference

Default Export

function jestToVitest(content: string | SgRoot, filename?: string): Promise<string>;

Transforms Jest code to Vitest. Accepts either a string of code or a parsed AST from @ast-grep/napi.

Named Exports

// Codemod configuration for use with codemod frameworks
export const JEST_TO_VITEST_CODEMOD: Codemod;

// AST language configuration (TypeScript)
export const JEST_TO_VITEST_LANGUAGE: Lang;

// Low-level transformation function
export function jestToVitestModifications(modifications: Modifications): Promise<Modifications>;

Behavior and Limitations

• File Detection: Only processes files that contain Jest global APIs (describe, it, expect, etc.)
• Language Support: Currently supports TypeScript syntax only
• Async Handling: Automatically converts functions to async when vi.importActual is used
• Import Optimization: Intelligently merges and organizes Vitest imports
• Project Setup: Post-transformation hooks set up Vitest configuration and dependencies

Development

Running Tests

pnpm test          # Run tests once
pnpm test:watch    # Run tests in watch mode
pnpm test:cov      # Run tests with coverage

Building

pnpm build         # Build the package
pnpm dev          # Build in watch mode

Code Quality

pnpm lint         # Lint code
pnpm format       # Format code
pnpm type-check   # Type check
pnpm quality      # Run all quality checks

Contributing

Contributions are welcome! Please open an issue or submit a pull request.

Development Setup

1. Clone the repository
2. Install dependencies: pnpm install
3. Run tests: pnpm test
4. Make your changes and ensure tests pass
5. Submit a pull request

License

This project is licensed under the MIT License.