QNetworkReply error return always NoError

I'm using QT 5 on the LinuxMint virtual machine for a console application.
I try to send a HTTP request to a web server using post().
It work perfectly but when I volontary create an error to test the soft (like disconnect the ethernet cable) My QNetworkReply instance return "NoError".
It's a problem because if it's always NoError I can't test the result.
I think it's a bug, but no totaly sure, it could be because of the virtual web connexion.