tst_QGraphicsScene::tabFocus_sceneWithNestedFocusWidgets() is flaky when removing setActiveWindow()

Tst_QGraphicsScene::tabFocus_sceneWithNestedFocusWidgets() is flaky when QApplicationPrivate::setActiveWindow(&widget) is removed. (see black screenshot)

However if the QTest::qWait(12) is increased to something like QTest::qWait(1500), the test passes every time without any issue.

NB: Even after qWait, we still have a widget.window()->windowHandle() , as can be verified with QDebug