You can use test integration and test mock, test stub and test integration commands to generate tests corresponding to entities.
You can find some information about developing add-ons in Spring Roo reference documentation. Spring Roo 1.1 Cookbook provides a more comprehensive coverage of developing add-ons for Spring Roo.
Currently, there is no undo command in Roo. As Roo logs all commands in the log.roo file of the project. You can modify the Roo commands in log.roo and execute the complete set of commands in log.roo by using script command.