Migrate test suite from Jest to Vitest

[TimothyJones]

This PR migrates the entire test suite from Jest to Vitest, modernizing the testing infrastructure and enabling better support for ESM modules.

Summary

The test framework has been completely replaced with Vitest, which provides better ESM support, faster test execution, and improved developer experience. All test files have been updated to use Vitest's API while maintaining the same test coverage and functionality.

Key Changes

• Test Framework Migration: Replaced Jest with Vitest across all test files

  • Updated jest.config.js → vitest.config.js with appropriate Vitest configuration
  • Configured Vitest with globals: true for Jest-compatible API
  • Set pool: 'forks' and concurrent: false for serial test execution

• Mock System Refactoring: Redesigned the mock infrastructure to work with both CJS and ESM

  • Refactored test/mocks/jest-mocks.js to export a setup() function that returns mock objects
  • Implemented a Node.js Module._load hook to intercept CJS require() calls in the source code's dependency graph
  • This allows vi.mock() (ESM-level) to work alongside CJS source code that uses require()
  • Added support for mocking run-execFile and fs modules with proper spy integration

• Test File Conversions: Converted all test files from CommonJS to ESM

  • Changed require() to import statements
  • Updated jest.spyOn() → vi.spyOn()
  • Updated jest.mock() → vi.mock() with proper module resolution
  • Used vi.hoisted() to set up mocks before module imports in integration tests
  • Added vi.resetModules() in integration tests to reload modules with fresh mocks

• ESLint Configuration: Updated to use eslint-plugin-vitest instead of eslint-plugin-jest

  • Updated globals configuration to use Vitest's environment globals
  • Adjusted rule configurations for Vitest compatibility

• Package.json Updates: Updated test scripts and dependencies

  • Changed test commands from jest to vitest run
  • Replaced Jest and jest-serial-runner with Vitest
  • Added eslint-plugin-vitest dependency

Notable Implementation Details

• The mock setup uses a CJS require hook because the source code is written in CommonJS with require() statements, while tests are now ESM. This hybrid approach ensures mocks work correctly across both module systems.
• Integration tests use vi.resetModules() before dynamic imports to ensure fresh module loads with current mock state
• The fs module is mocked at both the CJS hook level (for source code) and ESM level (for test code) to ensure consistent spy behavior
• Test timeout remains 30 seconds to maintain compatibility with existing test expectations

https://claude.ai/code/session_01JuGPaiD48RjuFRjujj7WU3