Test verifies that only ONE of pair messages is really added to firebird.log - 10053.
It seems that it is unable to implement test which will lead to appearance of 10054 because in such case engine keeps DB file opened after killing launched ISQL process which is done ES/EDS.
When this file has name = "initial" ('bugs.core_2493.fdb") then fb_test will raise exception on cleanup phase. Otherwise one can not to remove this (new) .fdb-file when test is finished.
It seems that DB file is kept opened such too long time only under fb_test env., so I will investigate this later.