Leaktests are software applications created to specifically check for methods and means to bypass personal firewall protection. Often the software is a group or suite of tests run in sequence. Usually leak tests are available online as free downloads or via a web interface if the tests can be run remotely. Sometimes the tests can be run by the average user who does not have expert knowledge of computer security. Others are intended for experts and professionals and it would be difficult for the average user to use correctly or to understand and evaluate the results. Some leak tests are performed by professionals to evaluate existing and new personal firewall software and publish the results for public review and comment. They do this both to inform the users, potential users, and to alert the creators of the software that there is room for improvement.
Some are well known and popular among those familiar or expert in computer security. For example, grc.com's LeakTest has been downloaded over 7 million times. You can read more about free security tests in my article: Top 10 Free Security Tests. My advice, if you don't understand the tests, the test results, or how to configure or change your personal firewall software: ask an expert! A false sense of security is a disaster waiting to happen.