Tomcat 7 embedded container is built with a dependency on Tomcat 7.0.20, which was released 2011-08-11. The latest version of Tomcat is 7.0.52, and a lot of patches have been applied since 7.0.20 (see changelog). When relying on the 7.0.52 version of Tomcat 7 embedded in your project, it would be preferable to use an adapter that is built using that version, as in some (at least theoretical) corner cases, Arquillian could fail running tests in a 7.0.52 embedded container.