Use the build.xml files, which are distributed with NexJ Studio, and run with Ant.
They contain targets for upgrading, validating, building, unit testing the model etc, which can be started by a continuous integration tool, like Jenkins.
The unit test view in studio runs metadata unit tests. Outside studio, unit tests can be run by invoking the ant target “app.test” in build/build.xml located in the studio plugin directory.
Using ant would be the best way to achieve CI using whatever CI platform you use to monitor code check-ins.
It is in ECLIPSE_HOME/plugins/com.nexjsystems.nexjstudio_*/enterprise/build/build.xml. This file includes …/core/build/build.xml, so the relevant targets will be in both files.