/usr/lib/mysql-testsuite/include/have_firstmatch.inc is in mysql-testsuite-5.6 5.6.16-1~exp1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | -- require r/have_optimizer_switch.require
--disable_query_log
select locate('firstmatch', @@optimizer_switch) > 0 AS OPTIMIZER_SWITCH;
--enable_query_log
|