public EditTestSystemViewModel(WorkspaceViewModel requester)
 {
     Requester = requester;
 }
 // for new message
 public NewMessageViewModel(WorkspaceViewModel requester, Window windowInstance)
 {
     Requester      = requester;
     WindowInstance = windowInstance;
     NewMessage     = new Message();
 }
 public NewUserViewModel(WorkspaceViewModel requester)
 {
     this.Requester = requester;
     this.NewUser   = new User();
 }