Dim Testlauf As New Test()
Dim TestRunThread = New Thread(AddressOf Testlauf.Run)
TestRunThread.Start()

Public Class Test
 
Public Sub New()
'
End Sub
 
Public Sub Run()
'
Mainform.Text = "TEST" 'Hier kommt eine Exception
Testfenster.lst_Ergebnisse_Add(1, 10, "Text", "Soll", "Ist", "Pass", _
  Color.Green)
End sub
 
End Class

'Delegates
    Private Delegate Sub dlg_lst_Ergebnisse_add(ByVal int_IconNr As Int16, _
      ByVal int_ZeilenNr As Int32, ByVal str_Text As String, ByVal str_SollText _
      As String, ByVal str_IstText As String, ByVal str_TestErgebnis As String, _
      ByVal col_Schriftfarbe As Color)    
 
Public Sub lst_Ergebnisse_Add(ByVal int_IconNr As Int16, ByVal int_ZeilenNr As _
  Int32, ByVal str_Text As String, ByVal str_SollText As String, ByVal _
  str_IstText As String, ByVal str_TestErgebnis As String, ByVal _
  col_Schriftfarbe As Color)
 
        If Me.lst_Ergebnisse.InvokeRequired Then
            Dim ext_lst_Ergebnisse_add As New dlg_lst_Ergebnisse_add(AddressOf _
              lst_Ergebnisse_Add)
            Me.Invoke(ext_lst_Ergebnisse_add, New Object() {int_IconNr, _
            int_ZeilenNr, str_Text,  str_SollText, str_IstText, _
            str_TestErgebnis, col_Schriftfarbe})
 
        Else
 
        Dim ListItem As New ListViewItem
        ListItem.UseItemStyleForSubItems = False
        ListItem = Me.lst_Ergebnisse.Items.Add("", int_IconNr)
        ListItem.SubItems.Add(CStr(int_ZeilenNr))
        ListItem.SubItems.Add(str_Text)
        ListItem.SubItems.Add(str_SollText)
        ListItem.SubItems.Add(str_IstText)
        ListItem.SubItems.Add(str_TestErgebnis)
        ListItem.ForeColor = col_Schriftfarbe
 
        End If
 
    End Sub