perl-Sys-Hostname-Long-1.5-6.fc27 fails to build in nspawned mock environment because a test fails there:

+ make test
PERL_DL_NONLAZY=1 "/usr/bin/perl" "-MExtUtils::Command::MM" "-MTest::Harness" "-e" "undef *Test::Harness::Switches; test_harness(0, 'blib/lib', 'blib/arch')" t/*.t
Can't exec "hostname": No such file or directory at lib/Sys/Hostname/Long.pm line 82.
Use of uninitialized value $tmp in transliteration (tr///) at lib/Sys/Hostname/Long.pm line 84.
Sys::Hostname::Long - Last Dispatch method = ip at lib/Sys/Hostname/Long.pm line 206.
Use of uninitialized value $hostname in string ne at t/local.t line 13.
# Failed test 1 in t/local.t at line 13
#  t/local.t line 13 is: ok($hostname ne "");
Use of uninitialized value $hostname in concatenation (.) or string at t/local.t line 15.
t/local.t .. 
Failed 1/1 subtests 

The nspawned mock mode is default in mock-1.4.1 and it probably isolate host network from the mock environment which is good. But then the Sys-Hostname-Long test fails because it does not have "hostname" program available and a fall back to resolving an local IP also fails because there is not local IP address.

Solution could be build-requiring (and run-recommending) "hostname" package.

Another option would be to patch the tests not to fail if a FQDN cannot be obtained because at the end this can happen in the real world.