anchor.diff:  tc() ->
       [send_ok,
        send_nok,
  +     send_bad_answer,
        send_arbitrary,
        send_unknown,
        send_unknown_mandatory,
  
positive.code:     #'diameter_base_answer-message'{'Result-Code' = ?INVALID_AVP_BITS}
          = call(Config, Req).
  
  %% Send an ASR with an arbitrary AVP and expect success and the same
  %% AVP in the reply.
  send_arbitrary(Config) ->
  
negative.code: 
  request(#diameter_base_accounting_ACR{'Session-Id' = SId,
                                        'Accounting-Record-Type' = RT,
                                        'Accounting-Record-Number' = 2 = RN},
          #diameter_caps{origin_host = {OH, _},
                         origin_realm = {OR, _}}) ->
      Ans = ['ACA', {'Result-Code', ?SUCCESS},
                    {'Session-Id', SId},
                    {'Origin-Host', OH},
                    {'Origin-Realm', OR},
                    {'Accounting-Record-Type', RT},
                    {'Accounting-Record-Number', RN}],
  
      {reply, #diameter_packet{header = #diameter_header{is_error = true},%% not
                               msg = Ans}};
  
  request(#diameter_base_accounting_ACR{'Session-Id' = SId,
                                        'Accounting-Record-Type' = RT,
                                        'Accounting-Record-Number' = RN},
          #diameter_caps{origin_host = {OH, _},
                         origin_realm = {OR, _}}) ->
  