ZenTest provides 4 different tools and 1 library: zentest, unit_diff, autotest, multiruby, and Test::Rails. ZenTest scans your target and unit-test code and writes your missing code based on simple naming rules, enabling XP at a much quicker pace. ZenTest only works with Ruby and Test::Unit. unit_diff is a command-line filter to diff expected results from actual results and allow you to quickly see exactly what is wrong. autotest is a continous testing facility meant to be used during development. As soon as you save a file, autotest will run the corresponding dependent tests. multiruby runs anything you want on multiple versions of ruby. Great for compatibility checking! Test::Rails helps you build industrial-strength Rails code.