public static async Task<TestResult> TestConnection (Uri url, IWebDavClient webDavClient, ResourceType supposedRessourceType)
    {
      var calDavDataAccess = new CalDavDataAccess (url, webDavClient);
      var cardDavDataAccess = new CardDavDataAccess (url, webDavClient);

      TestResult result;


      switch (supposedRessourceType)
      {
        case ResourceType.None:
          var ressourceType =
              (await calDavDataAccess.IsResourceCalender() ? ResourceType.Calendar : ResourceType.None) |
              (await cardDavDataAccess.IsResourceAddressBook() ? ResourceType.AddressBook : ResourceType.None);

          result = new TestResult (
              ressourceType,
              ressourceType.HasFlag (ResourceType.Calendar) ? await GetCalendarProperties (calDavDataAccess) : CalendarProperties.None,
              ressourceType.HasFlag (ResourceType.AddressBook) ? await GetAddressBookProperties (cardDavDataAccess) : AddressBookProperties.None);
              break;

        case ResourceType.Calendar:
          result = new TestResult (
              supposedRessourceType,
              CalendarProperties.CalendarAccessSupported |
              (await calDavDataAccess.IsWriteable() ? CalendarProperties.IsWriteable : CalendarProperties.None) |
              (await calDavDataAccess.DoesSupportCalendarQuery() ? CalendarProperties.SupportsCalendarQuery : CalendarProperties.None),
              AddressBookProperties.None);
          break;
        
        case ResourceType.AddressBook:
          result = new TestResult (
              supposedRessourceType,
              CalendarProperties.None,
              AddressBookProperties.AddressBookAccessSupported |
              (await cardDavDataAccess.IsWriteable() ? AddressBookProperties.IsWriteable : AddressBookProperties.None));
          break;
        
        default:
          throw new ArgumentOutOfRangeException ("supposedRessourceType");
      }

      return result;
    }
    public static async Task<TestResult> TestConnection (Uri url, IWebDavClient webDavClient, ResourceType autoRessourceType)
    {
      var calDavDataAccess = new CalDavDataAccess (url, webDavClient);
      var cardDavDataAccess = new CardDavDataAccess (url, webDavClient);

      TestResult result;

      if (autoRessourceType == ResourceType.None)
      {
        var ressourceType =
          (await calDavDataAccess.IsResourceCalender() ? ResourceType.Calendar : ResourceType.None) |
          (await cardDavDataAccess.IsResourceAddressBook() ? ResourceType.AddressBook : ResourceType.None);

        result = new TestResult(
          ressourceType,
          ressourceType.HasFlag(ResourceType.Calendar) ? await GetCalendarProperties(calDavDataAccess) : CalendarProperties.None,
          ressourceType.HasFlag(ResourceType.AddressBook) ? await GetAddressBookProperties(cardDavDataAccess) : AddressBookProperties.None);
      }
      else if (autoRessourceType == ResourceType.Calendar)
      {
        result = new TestResult(
          autoRessourceType,
          CalendarProperties.CalendarAccessSupported |
          (await calDavDataAccess.IsWriteable() ? CalendarProperties.IsWriteable : CalendarProperties.None) |
          (await calDavDataAccess.DoesSupportCalendarQuery() ? CalendarProperties.SupportsCalendarQuery : CalendarProperties.None),
          AddressBookProperties.None);
      }
      else
      {
        result = new TestResult(
          autoRessourceType,
          CalendarProperties.None,
          AddressBookProperties.AddressBookAccessSupported |
          (await cardDavDataAccess.IsWriteable() ? AddressBookProperties.IsWriteable : AddressBookProperties.None));
      }

      return result;
    }
 private static async Task<AddressBookProperties> GetAddressBookProperties (CardDavDataAccess cardDavDataAccess)
 {
   return
       (await cardDavDataAccess.IsAddressBookAccessSupported() ? AddressBookProperties.AddressBookAccessSupported : AddressBookProperties.None) |
       (await cardDavDataAccess.IsWriteable() ? AddressBookProperties.IsWriteable : AddressBookProperties.None);
 }
    private async Task<bool> TestAddressBook (CardDavDataAccess cardDavDataAccess, StringBuilder errorMessageBuilder)
    {
      bool hasError = false;
      if (!await cardDavDataAccess.IsAddressBookAccessSupported())
      {
        errorMessageBuilder.AppendLine ("- The specified Url does not support addressbook.");
        hasError = true;
      }

      if (!await cardDavDataAccess.IsWriteable())
      {
        errorMessageBuilder.AppendLine ("- The specified Url is a read-only addressbook.");
        hasError = true;
      }

      if (_folderType != OlItemType.olContactItem)
      {
        errorMessageBuilder.AppendLine ("- The outlook folder is not a address book, or there is no folder selected.");
        hasError = true;
      }
      return hasError;
    }