Watchdog
Watchdog is a set of validation tests that can be run against a Servlet 2.3 / JSP 1.2 container (such as Tomcat 4.0 or Tomcat 4.1) to identify potential problems with conformance to the corresponding specifications. While it is not the official TCK for the Servlet or JSP specifications, the tests it performs are similar.
Official Project Page: http://jakarta.apache.org/watchdog/index.html