Live feedback on behavioral changes

The costs to find and fix bugs grows over time, to the point where fixing a bug after release may cost as much as 100 times more than before release. To help programmers find bugs as soon as they are introduced, we sketch a plugin for an integrated development environment that provides live feedback about behavioral changes to Java programs by continuously generating tests, running the tests on the current and previous versions of the program, and comparing the results. Such a tool would allow programmers to better understand how their changes affect the behavior of their programs. As a proof of concept, we developed a prototype that found a bug that remained undetected by pair programmers working on JHotDraw in a previous study. Had the programmers performed this change with our plugin, they would have been notified about the bug as soon as they introduced it.