I'm assuming that's only part of the file and you may have multiple testsuite elements. I don't understand the example though as I would have expected the testsuite time and counts to be the sum the testcases.

#!perl
use strict;
use XML::Twig;

my $t = XML::Twig->new( twig_handlers => 
    { 'testcase'  => \&testcase,
      'testsuite' => \&testsuite,
    },
    pretty_print => 'indented',);

$t->parsefile( 'test.xml' );
$t->print_to_file('new.xml');
$t->print();

my @case=();
sub testcase {
  my ($t,$e) = @_;
  push @case,$e->cut;
};

sub testsuite {
  my ($t,$e) = @_;
  while ($_ = pop @case){
    $_->paste($e);
  }
};
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