There is a request to provide a "mini test harness" based on javatest (CR #7124176).
The current design doesn't allow to select a subset of GUI independent classes that could be bundled into a harness, because some core classes uses swing or awt.
The good news, there not that many such classes and they could be refactored:

1) com.sun.javatest.tool.Preferences
Has inner class Preferences.Pane to edit preferences.
Suggestion: move Preferences.Pane --> PreferencesPane


2) com.sun.javatest.agent.AgentMonitorCommandManager -
provides several commands to work with agent, one command is "ShowMonitor" which requires com.sun.javatest.tool.Desktop to display agent state.
Suggestion: separate GUI independent commands into a base class, which AgentMonitorCommandManager will extract.

3) com.sun.javatest.logging.ObservableFile
uses javax.swing.event.EventListenerList to store list of FileListener objects.
Suggestion: replace EventListenerList with List<FileListener>