title: How to hide a QDialog (not showing GUI) on exec()
body: <p>I want to exec() a QDialog without GUI for my test - there's no need to show GUI.</p>
  
  <p>In the main window, when I exec() a QDialog, it shows its GUI window. I connect a signal from thread in QDialog to a slot in QDialog, so QDialog.exec() is needed. QDialog.hide() is not working.</p>
  
  <p>Is there any solution?</p>