This is failing repeatably on Linux - Ubuntu 17.10
Possibly it is sensitive to other windows on the desktop ?
My browser window was brought to the front when it was running.
Logs vary .. here is one :
Any messages for the tester will display here.
java.awt.event.FocusEvent[FOCUS_GAINED,permanent,opposite=java.awt.TextArea[text0,0,28,657x242,text=This is an automatic test. Simply wait until it's done.
,editable,selection=0-0,rows=15,columns=80,scrollbarVisibility=both],cause=ACTIVATION] on button0
Clicking java.awt.Button[button0,0,0,100x100,label=button1]
Clicking java.awt.Button[button1,0,0,100x100,label=button2]
java.awt.event.FocusEvent[FOCUS_GAINED,permanent,opposite=java.awt.Button[button0,0,0,100x100,label=button1],cause=ACTIVATION] on button1
Test for frame0 passed.
java.awt.event.FocusEvent[FOCUS_GAINED,permanent,opposite=null,cause=ACTIVATION] on button2
Clicking java.awt.Button[button2,0,0,100x100,label=button1]
Clicking java.awt.Button[button3,0,0,100x100,label=button2]
----------System.err:(6/477)----------
java.lang.RuntimeException: Test failed: window2 is not focusable!
at WindowUpdateFocusabilityTest.test(WindowUpdateFocusabilityTest.java:139)
at WindowUpdateFocusabilityTest.start(WindowUpdateFocusabilityTest.java:79)
at com.sun.javatest.regtest.agent.AppletWrapper$AppletRunnable.run(AppletWrapper.java:157)
at java.base/java.lang.Thread.run(Thread.java:832)
STATUS:Failed.Applet thread threw exception: java.lang.RuntimeException: Test failed: window2 is not focusable!
----------rerun:(24/1694)*----------