Mochapack is a test runner that combines Mocha with Webpack to precompile test files before execution, providing automatic source-map handling and optimized file-watching capabilities. It's designed for JavaScript developers working with Webpack who want to run tests without writing intermediate files to disk and benefit from intelligent test selection when code changes. The tool is particularly useful for projects using modern JavaScript tooling, offering features like glob pattern support, near-identical Mocha CLI interface, and enhanced watch mode that only re-runs affected tests when files change.