anchor.diff:      ?answer_message(?TOO_BUSY)
           = call(Config, Req).
   
  -%% Send an STR containing a known AVP, but one that's not allowed and
  -%% sets the M-bit.
  -send_unrecognized_mandatory(Config) ->
  +%% Send an STR containing a known AVP, but one that's not expected and
  +%% that sets the M-bit.
  +send_unexpected_mandatory(Config) ->
       Req = ['STR', {'Termination-Cause', ?LOGOUT}],
   
       ['STA', _SessionId, {'Result-Code', ?AVP_UNSUPPORTED} | _]
  
positive.code:        N == send_zero_avp_length;
         N == send_invalid_avp_length;
         N == send_invalid_reject;
         N == send_unknown_short_mandatory ->
      Rec;
  answer(Rec, [], _) ->
      Rec.
  
negative.code:     <<V, L:24, H/binary>> = H0,  %% assert
      E#diameter_packet{bin = <<V, (L+4):24, H/binary, 16:24, 0:32, T/binary>>};
  
  prepare(Pkt, Caps, send_unexpected_mandatory, #group{client_dict0 = Dict0}
                                                = Group) ->
      Req = prepare(Pkt, Caps, Group),
      #diameter_packet{bin = <<V, Len:24, T/binary>>}
          = E
  