The problem must be somewhere else because the code as you posted it compiles just fine:

use Test::More;

sub _test_bug_exists
{
   my $args = shift;
   my $bug = get_bug( $args->{bug} );

   subtest 'Lookup existing bug' => sub # this is line 241
   {
      is( $bug->{response}, "$c->{bug_tracker}/$args->{bug}",
         "URL correct?" );
      is( $bug->{subject}, "Variables not expanded inside array",
         "Subject correct?" );
   }
}
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> perl -wc tmp.pl
Name "main::c" used only once: possible typo at tmp.pl line 10.
tmp.pl syntax OK
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