Mistletoe is a junit extension intended for integration testing. In technical terms, mistletoe is a junit test suite runner presenting the test results via HTTP as a web-page.
Mistletoe, when incorporated within an application will help diagnose integration issues. For example, an application which runs perfectly in the developer's environment may not run properly in the production environment due to configuration errors and connectivity issues. Instead of perusing log files, or looking at stack traces, mistletoe will run a user-specified series of tests and present the results in the form of a web-page served by the application itself. Since the tests are run within the context of the deployed application, given an appropriate test suite, you can home in on integration problems quickly and conveniently.
See the user manual for details.