private void assertDialogNotShown() {
    assertSame(null, dialogControl.getWorkbench());
    assertSame(0, workbench.getBlockingOverlaysShown().size());
    assertSame(0, workbench.getNonBlockingOverlaysShown().size());
  }
Internal utility method for testing.
Simulates closing the stage, which fires a close request to test logic
inside of {@link Stage#setOnCloseRequest(EventHandler)}.
Using {@link FxRobot#closeCurrentWindow()} would be better, but it only works on Windows
because of its implementation, so this approach was chosen as a workaround.
@see <a href="https://github.com/TestFX/TestFX/issues/447">
closeCurrentWindow() doesn't work headless</a>
workbenchfx-core/src/test/java/com/dlsc/workbenchfx/WorkbenchTest.java