use warnings;
use strict;
use Test::More tests=>7;
use Digest::MD5;
use Class::Method::Modifiers;

my $cnt = 0;
before 'Digest::MD5::hexdigest' => sub { $cnt++ };

my $d1 = Digest::MD5->new;
$d1->add("1");
$d1->add("1");
is $d1->hexdigest, "6512bd43d9caa6e02c990b0a82652dca";
is $d1->hexdigest, "d41d8cd98f00b204e9800998ecf8427e";
is $cnt, 2;

use Memoize;
memoize('Digest::MD5::add');
memoize('Digest::MD5::hexdigest');

# the *exact same* tests as above!
my $d2 = Digest::MD5->new;
$d2->add("1");
$d2->add("1");
# now we get the MD5 sum of "1" instead of "11"
is $d2->hexdigest, "6512bd43d9caa6e02c990b0a82652dca";
# hexdigest should reset the state of the object
is $d2->hexdigest, "d41d8cd98f00b204e9800998ecf8427e";

$cnt = 0;
my $d3 = Digest::MD5->new;
# "hexdigest" was memoized above, so should we get the MD5 sum of
# "" or of "1"? Also, should $cnt be incremented or not?
is $d3->hexdigest, "c4ca4238a0b923820dcc509a6f75849b";
is $cnt, 0;

__END__

1..7
ok 1
ok 2
ok 3
not ok 4
#   Failed test at m.pl line 27.
#          got: 'c4ca4238a0b923820dcc509a6f75849b'
#     expected: '6512bd43d9caa6e02c990b0a82652dca'
not ok 5
#   Failed test at m.pl line 29.
#          got: 'c4ca4238a0b923820dcc509a6f75849b'
#     expected: 'd41d8cd98f00b204e9800998ecf8427e'
not ok 6
#   Failed test at m.pl line 35.
#          got: 'd41d8cd98f00b204e9800998ecf8427e'
#     expected: 'c4ca4238a0b923820dcc509a6f75849b'
not ok 7
#   Failed test at m.pl line 36.
#          got: '1'
#     expected: '0'
# Looks like you failed 4 tests of 7.