anchor.diff:          = call(Config, Req).
   
   %% Send an ACR that the server callback answers explicitly with a
  -%% protocol error.
  +%% protocol error and some AVPs to check the decoding of.
   send_protocol_error(Config) ->
       Req = ['ACR', {'Accounting-Record-Type', ?EVENT_RECORD},
                     {'Accounting-Record-Number', 4}],
   
       ['answer-message' | #{'Result-Code' := ?TOO_BUSY,
  -                          'AVP' := [OLR]}]
  +                          'AVP' := [OLR | _]} = Avps]
           = call(Config, Req),
   
       #diameter_avp{name = 'OC-OLR',
  
positive.code:             'OC-Reduction-Percentage' => [25],
              'OC-Validity-Duration' => [60],
              'AVP' => [{'OC-Supported-Features', []}]},
      Ans = ['answer-message', {'Result-Code', ?TOO_BUSY},
                               {'Origin-Host', OH},
                               {'Origin-Realm', OR},
                               {'AVP', [{'OC-OLR', OLR}]}],
      {reply, Ans};
  
  %% send_proxy_info
  
negative.code:     #diameter_avp{name = 'OC-Supported-Features',
                    value = #{} = Fs}
          = OSF,
      0 = maps:size(Fs),
  
      #group{client_dict = D} = group(Config), 
  
      if D == nas4005 ->
              error = maps:find('Failed-AVP', Avps),
              #{'AVP' := [#diameter_avp{name = 'Failed-AVP',
                                        value = #{'AVP' := [_,NP]}}]}
                  = Avps,
              #diameter_avp{name = 'NAS-Port', value = 44}
                  = NP;
              
         D == diameter_gen_base_rfc3588;
         D == diameter_gen_basr_accounting ->
              error = maps:find('Failed-AVP', Avps),
              #{'AVP' := [#diameter_avp{name = 'Failed-AVP',
                                        value = #{'AVP' := [_,NP]}}]}
                  = Avps,
              #diameter_avp{name = undefined, value = undefined}
                  = NP;
  
         D == diameter_gen_base_rfc6733;
         D == diameter_gen_acct_rfc6733 ->
              error = maps:find('AVP', Avps),
              #{'Failed-AVP' := [#{'AVP' := [NP]}],
                'AVP' := [_]}
                  = Avps,
              #diameter_avp{name = undefined, value = undefined}
                  = NP
      end.
  
  %% Send a 3xxx Experimental-Result in an answer not setting the E-bit
  %% and missing a Result-Code.
  