Sometimes you are expecting to get a value but you don't really know what. You just know one specific value that you want to make sure you have not received.

use strict;
use warnings;

use lib 'lib';
use MyTools;

use Test::More tests => 3;

foreach my $str ('Deep Purple', 'Beatles', 'ABBA') {
    isnt(scramble($str), $str,     $str);


ok 1 - Deep Purple
ok 2 - Beatles
not ok 3 - ABBA
#   Failed test 'ABBA'
#   at t/isnt.t line 10.
#     'ABBA'
#         ne
#     'ABBA'
# Looks like you failed 1 test of 3.

This isn't a good example though.