This old DnD test (closed/java/awt/dnd/DropActionChangedTest/DropActionChangedTest) for some reason hangs in javatest on shutdown, on Mac. Most probably it is even a javatest issue rather than Mac port one, but anyway I know a workaround.
If you add some frame.setVisible(false) or even (true) after DnD action finished, everything ends properly and fast.