This test fails rather often e.g. on Ubuntu -- actually, it doesn't matter what is the system. There should be two simple things in the test:
autodelay between robot events;
realsync/short delay immediately after Robot creation.
Something like
diff -r 4fe836518d72 javax/swing/JTree/4633594/bug4633594.java
--- a/javax/swing/JTree/4633594/bug4633594.java Thu Dec 22 08:26:06 2016 +0000
+++ b/javax/swing/JTree/4633594/bug4633594.java Mon Dec 26 15:17:02 2016 +0300
@@ -47,6 +47,8 @@
             }
 
             robot = new Robot();
+ robot.setAutoDelay(50);
+ robot.delay(150);
             robot.keyPress(KeyEvent.VK_DOWN);
             robot.keyRelease(KeyEvent.VK_DOWN);
             robot.keyPress(KeyEvent.VK_RIGHT);


RULE "closed/javax/swing/JTree/4633594/bug4633594.java" Exception java.lang.Error: Focus wasn't transferred to the proper component