What you intended to be constant names are getting parsed as literal strings.

use strict;
use warnings;

use constant CONST1=>10;
use constant CONST2=>12;

my %var=(
CONST1=>'test1',
CONST2=>'test2',
);

use Data::Dumper;
print Dumper \%var;
__END__
$VAR1 = {
          'CONST1' => 'test1',
          'CONST2' => 'test2'
        };
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Internally, constants are functions. You can force them to be recognized by using function syntax:

my %var=(
CONST1()=>'test1',
CONST2()=>'test2',
);

print $var{CONST1()}."\n";
print $var{10}."\n";

use Data::Dumper;
print Dumper \%var;
__END__
test1
test1
$VAR1 = {
          '10' => 'test1',
          '12' => 'test2'
        };
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Or, as I personally prefer:

my %var=(
(CONST1)=>'test1',
(CONST2)=>'test2',
);

print $var{(CONST1)}."\n";
print $var{10}."\n";
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