perlbrewed Perl 5.16.2 64bit with -Dusethreads.
Both methods return two directories whereas the test checks for one:
[ahartmai@ahartmai-nb:~/.cpanplus/5.16.2/build/File-ConfigDir-0.004$ ]$
prove -vl t/01-simple.t
t/01-simple.t ..
ok 1 - Can config_dirs
# config_dirs: /etc,/etc/xdg,/usr/local/etc,/home/ahartmai
ok 2 - config_dirs
ok 3 - Can system_cfg_dir
# system_cfg_dir: /etc
ok 4 - system_cfg_dir
ok 5 - Can desktop_cfg_dir
# desktop_cfg_dir: /etc/xdg/xdg-ubuntu,/etc/xdg
not ok 6 - desktop_cfg_dir
ok 7 - Can core_cfg_dir
# core_cfg_dir: .../../etc
ok 8 - core_cfg_dir
ok 9 - Can site_cfg_dir
# site_cfg_dir:
/home/ahartmai/perl5/perlbrew/perls/perl-5.16.2/lib/site_perl/etc
ok 10 - site_cfg_dir
ok 11 - Can vendor_cfg_dir
# vendor_cfg_dir: /etc
ok 12 - vendor_cfg_dir
ok 13 - Can local_cfg_dir
# local_cfg_dir: /usr/local/etc
ok 14 - local_cfg_dir
ok 15 - Can here_cfg_dir
# here_cfg_dir:
/home/ahartmai/.cpanplus/5.16.2/build/File-ConfigDir-0.004/etc
ok 16 - here_cfg_dir
ok 17 - Can singleapp_cfg_dir
# singleapp_cfg_dir: etc
ok 18 - singleapp_cfg_dir
ok 19 - Can xdg_config_dirs
# xdg_config_dirs: /etc/xdg/xdg-ubuntu,/etc/xdg
not ok 20 - xdg_config_dirs
ok 21 - Can xdg_config_home
# xdg_config_home: 1
ok 22 - xdg_config_home
ok 23 - Can user_cfg_dir
# user_cfg_dir: /home/ahartmai
ok 24 - user_cfg_dir
1..24
# Failed test 'desktop_cfg_dir'
# at t/01-simple.t line 41.
# /etc/xdg/xdg-ubuntu,/etc/xdg
# Failed test 'xdg_config_dirs'
# at t/01-simple.t line 41.
# /etc/xdg/xdg-ubuntu,/etc/xdg
# Looks like you failed 2 tests of 24.
Dubious, test returned 2 (wstat 512, 0x200)
Failed 2/24 subtests
Test Summary Report
-------------------
t/01-simple.t (Wstat: 512 Tests: 24 Failed: 2)
Failed tests: 6, 20
Non-zero exit status: 2
Files=1, Tests=24, 0 wallclock secs ( 0.02 usr 0.01 sys + 0.04 cusr
0.01 csys = 0.08 CPU)
Result: FAIL