public void StartUp() { cnxStringSetting1 = new ConnectionStringSettings("MyCnxString", "Data Source=ServerName;Initial Catalog=DataBaseName;Integrated Security=SSPI;" , "System.Data.SqlClient"); cnxStringSetting2 = new ConnectionStringSettings("MyCnxStringTest", "Data Source=ServerName;Initial Catalog=DataBaseName;Integrated Security=SSPI;" , "System.Data.SqlClient"); // Create an set of ConnectionString var cnxString = ConfigurationManager.ConnectionStrings; var field = typeof(ConfigurationElementCollection).GetField("bReadOnly", BindingFlags.Instance | BindingFlags.NonPublic); field.SetValue(cnxString, false); cnxString.Clear(); cnxString.Add(cnxStringSetting1); cnxString.Add(cnxStringSetting2); cnxStringWrapper = new ConnectionStringSettingsCollectionWrapper(cnxString); }