JSUnit is a unit testing framework for JavaScript. Testing JavaScript manually is time-consuming and prone to errors, but JSUnit provides the developer a simpler, automated way of doing unit tests to ensure thorough testing at a fraction of the time it would take to test manually. JSUnit allows for the execution of automated tests for multiple browsers and operating systems.
JWebUnit is a Java-based testing framework for web applications. It wraps existing testing frameworks such as HtmlUnit and Selenium with a unified, simple testing interface to allow you to quickly test the correctness of your web applications.
HtmlUnit is a "GUI-Less browser for Java programs". It models HTML documents and provides an API that allows you to invoke pages, fill out forms, click links, etc… just like you do in your "normal" browser. It has fairly good JavaScript support (which is constantly improving) and is able to work even with quite complex AJAX libraries, simulating either Firefox or Internet Explorer depending on the configuration you want to use. HtmlUnit is not a generic unit testing framework. It is specifically a way to simulate a browser for testing purposes and is intended to be used within another testing framework such as JUnit or TestNG. Refer to the document "Getting Started with HtmlUnit" for an introduction.
