This works (mostly); I found indentation on the root node breaks it but it might be right for what you're doing.

use strict;
use warnings;
use XML::LibXML;
use Test::More tests => 2;

my $parser = XML::LibXML->new();
$parser->keep_blanks(1);

my $dom_one = $parser->parse_string(xml_one());

is( $dom_one->serialize(), xml_one(),
    "Serialized xml_one is the same as original" );

my $dom_two = $parser->parse_string(xml_two());
is( $dom_two->serialize(), xml_two(),
    "Serialized xml_two is the same as original" );

sub xml_one {
    <<"";
<?xml version="1.0"?>
<stuff>
  <andjunk>
muhuminah
  </andjunk>
</stuff>

}

sub xml_two {
    <<"";
<?xml version="1.0"?>
<stuff>
                           <andjunk>
     muhuminah</andjunk>
                          </stuff>

}
__END__
1..2
ok 1 - Serialized xml_one is the same as original
ok 2 - Serialized xml_two is the same as original
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