Sql Server Custom code Issue in SSRS

Hi there:
  In the Code tab in Report Properties, I have the following code:

Function DBConnect() As System.Data.SqlClient.SqlConnection
        Dim connectionstring As String
        connectionstring = "server=lafap; database=astea8l; uid=re; pwd=v8;"  
        Dim cn As New System.Data.SqlClient.SqlConnection(connectionstring)
        Return cn
End Function

Function test() as String
    Dim cn As New System.Data.SqlClient.SqlConnection
    cn.Open()
    cn.Close()
    return "Connected"
END Function

Also , in the reference tab, I've referenced the System.Data.
in the layout, I put =code.test() into one of the table field. And SSRS gives me the following error:

The value expression for the textbox textbox4 contains an error: The ConnectionString property has not been initialized.

Does someone have any idea how to get rid of this error?
 Also any recommendations on the debug env. for Custom Code?

 Thanks a lot

 Hui