anchor.diff:                               UserId2 -> {ok, #{
                                              credential => [Cred],
                                              error => <<>>}, []};
  +                             UserId3 -> {ok, #{credential => [Cred]}, []};
                                _ -> {error, just_because, []}
                            end
                    end,
  +    AllowSame = fun(ServiceId) ->
  +                            case ServiceId of
  +                                ServiceId1 -> true;
  +                                _ -> false
  +                            end
  +                    end,
       ok = test_util:meck_new(MeckModules),
       ok = meck:expect(tts_data_sqlite, credential_add, AddFun),
       ok = meck:expect(tts_data_sqlite, credential_get_count, fun(_, _) -> {ok, 0} end),
  
positive.code:     UserId1 = <<"foo">>,
      UserId2 = <<"bar">>,
      UserId3 = <<"joe">>,
      UserInfo1 = #{site => #{uid => UserId1}},
      UserInfo2 = #{site => #{uid => UserId2}},
      UserInfo3 = #{site => #{uid => UserId3}},
      CredState = <<"some_cred">>,
      Cred = <<"secret">>,
      MeckModules = [tts_data_sqlite, tts_cred_sup, tts_cred_worker, tts_service],
  
negative.code:     Params = [],
      MyPid = self(),
      Interface = <<"test interface">>,
      AddFun = fun(User, Service, IFace, State, _AllowMultiple) ->
                       IFace = Interface,
                       User = UserId1,
                       Service = ServiceId,
  