I'm off on a tangent here, so please excuse the off-topicness of this quick example.

How do you test your shuffling or die rolling technique is fair and produces results according to your specifications (say, according to a Gaussing distribution), and isn't biased favouring certain outcomes?

By using Test::LectroTest! Given this trivial implementation of an n-sided die, which returns a number between 1 and the number of sides on your die. Default number of sides is 6.

package Die;

sub new {
    my ( $pck, $sides ) = @_;

    return bless( { sides => $sides || 6 }, $pck );
}

sub roll {
    my ( $self ) = @_;
    return int( rand( $self->{ sides } ) ) + 1;
}

1;
[download]

We then express how we want our die to perform with a Test::LectroTest property that generates a thousand tests with dies with from 1 to 100 sides. We roll the die, and check that the result is legal for this kind of die (eg. within the limits). The second propery generates a thousand six sided dies and rolls each of them once. The results are stored in the the LectroTest controller object with the tcon->label()-call, that automatically spits out the distribution of the roll.

#! /usr/bin/perl

use Test::LectroTest;
use Die;

Property {
  ##[ x <- Int( range => [ 1, 100 ], sized => 0 ) #]##
  my $die = Die->new( $x );
  my $roll = $die->roll();

  ( 0 < $roll && $x >= $roll );
}, name => "My die returns something between 1 and the number of sides
+ of the die.";

Property {
  ##[ x <- Unit( 6 ) #]##
  my $die = Die->new( $x );
  my $roll = $die->roll();

  $tcon->label( $roll );

  ( 0 < $roll && $x >= $roll );
}, name => "With a six sided die, I get this distribution";
[download]

When I run this, I get:

1..2
ok 1 - 'My die returns something between 1 and the number of sides of 
+the die.' (1000 attempts)
ok 2 - 'With a six sided die, I get this distribution' (1000 attempts)
#  18% 2
#  17% 3
#  16% 1
#  16% 5
#  16% 6
#  15% 4
[download]

What this means is that the number 2 showed up 18% of the time, 3 17% etc. The numbers don't add up to a 100%, but I presume this is because of rounding in the presentation. In any case, this looks like acceptable behavior for a six sided die to me. I'm sure it's possible to automatically analyze the distribution and build this into the test, but I don't have the time to find out how right now. And please remember that this example was hacked together in a hurry, so I'm sure it can be improved.

I like Test::LectroTest :)

Edit: Removed an erroneous line in the second property.

Retitled by davido from 'OT: Test::LectroTest and pseudo random distributions'.