The test/jdk/javax/swing/JFrame/DefaultCloseOperation.java test could be improved:

In fact, I thought about iterating the values automatically ... and ask the tester to click the Close button on the window. The do nothing could be the last option tested, and the frame/dialog would be closed from the handler.

Another way could be sending the event programmatically. This would automate the test completely. However, we may still leave the manual test... just in case the tester sees anything unusual.

See https://github.com/openjdk/jdk/pull/15827#discussion_r1336149065 from JDK-8316211 for more details.