As I thought some of you might be in need of something like this, I decided to share this simple, but yet useful task.
As the repository hosting the project this task has been developed for is not yet open to the public, I just uploaded the Phing task file, which can be downloaded below.
A simple buildfile using the jstestdriver task does look like this:
<project name="some project" default="test" basedir=".">
<taskdef name="jstestdriver" classname="phing.tasks.jsTestDriverTask"/>
<include name="build.js" />
<include name="this/*.js" />
<include name="that/*.js" />
<include name="something_else/*.js" />