Testing a hash to see if it has values for all required keys. Extraneous keys are okay.

use strict;
use warnings;
use Test::More tests => 3;

my (%required,%over,%under,%partial);
$required{$_} = 1 for qw/header detail trailer/;

$over{$_} = $_ for qw/title header subject detail trailer postscript/;
$under{$_} = $_ for qw/header trailer/;
$partial{$_} = $_ for qw/header trailer/;
$partial{detail} = undef;

ok(test_it(%over),'checking %over for required keys');
ok(test_it(%under),'checking %under for required keys');
ok(test_it(%partial),'checking %partial for required keys');

sub test_it {
  my %h = @_;
#  return (grep {$required{$_} && $h{$_}} keys %h) == (keys %required)
+;
   return (grep {$required{$_} && defined $h{$_}} keys %h) == (keys %r
+equired);
}
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Update: use of defined suggested by choroba. I would have run into this because 0 is a value I would encounter.