RFR: 8351357: Add canary system test checking if Stage receives focus on show [v2]

[Andy Goryachev]

On Wed, 18 Jun 2025 07:04:25 GMT, Lukasz Kostyra <lkostyra at openjdk.org> wrote:

>> tests/system/src/test/java/test/robot/javafx/stage/StageFocusTest.java line 110:
>> 
>>> 108:     public void testStageHasFocusAfterShow() {
>>> 109:         Util.sleep(250);
>>> 110:         Util.runAndWait(() -> {
>> 
>> If the stage isn't focused after the sleep the robot's key press might go to some other app entirely. You might want to add an assert after the sleep checking that stage.isFocused() returns true.
>
> I checked this and it actually is a bug, `isFocused()` returns true in this case (when the Stage is not focused). We don't capture the failure of `SetForegroundWindow()`, so JFX assumes we are in focus. It doesn't necessarily change the outcome of the test, the key press check will then fail, but it would be good for the flag to also reflect that.
> 
> I'll add the assertion and file a separate issue for that.

I wonder if we could paint the window in some unusual color and check the screen pixels to make sure the window is on top, in addition to being focused?

-------------

PR Review Comment: https://git.openjdk.org/jfx/pull/1804#discussion_r2172400511