use strict;
use warnings;

my %h = (
	 'this is a test' => 2,
	 'is a test' => 2,
	 'a test' => 1
	);

my @keys = sort {length $a <=> length $b} keys %h;

for ( 0 .. $#keys-1){
  if ($keys[$_+1] =~ /$keys[$_]/){
    delete $h{$keys[$_]};
  }
}