JMock

Generates over 2 million user records per second in a single thread, as stated in the README, making it ideal for high-volume data needs like performance testing.

Produces data that accurately mimics real-world business scenarios with built-in internationalization support, ensuring reliable testing for global applications.

Supports both annotation-based field definitions and function-based script files, allowing developers to choose the approach that best fits their workflow, as highlighted in the core features.

Features a plugin-based system for adding custom mock data functions, enabling easy extension and customization beyond built-in capabilities.