为什么我的全局变量没有在Test::Class中初始化?

下面是一个使用一些全局变量/常量的简单测试用例:

use strict;
use warnings;
use base 'Test::Class';
use Test::More;

__PACKAGE__->runtests() unless caller;

my $ONE = "1";
my $TWO;

sub setup : Test(setup) {
    $TWO = "2";
}

sub test_me : Tests {
    is("1", $ONE);
    is("2", $TWO);
}

$ONE 未初始化:

robert@saaz:~$ prove test.t 
test.t .. 1/? 
#   Failed test 'test me'
#   at test.t line 16.
#   (in main->test_me)
#          got: '1'
#     expected: undef
# Looks like you failed 1 test of 2.
test.t .. Dubious, test returned 1 (wstat 256, 0x100)
Failed 1/2 subtests 

Test Summary Report
-------------------
test.t (Wstat: 256 Tests: 2 Failed: 1)
  Failed test:  1
  Non-zero exit status: 1
Files=1, Tests=2,  0 wallclock secs ( 0.02 usr  0.00 sys +  0.05 cusr  0.00 csys =  0.07 CPU)
Result: FAIL

为什么?很明显,这个变量是被定义的(否则我会因为 use strict;

Test::Class 测验?