it is to be expected that libgd and/or the GD::Image wrapper around that library together have sufficient tests on copyResampled to ensure that it works in any situation they claim it will work

I think that's the key...
I have been getting too focussed on testing everything but I don't need to test the things that are out of the control of my module!

Following on from your 3 points I have tried this approach... 

use strict;
use warnings;

use Test::More;

use GD::Simple;
use Image::Square;

plan tests => 3;

my $horizontal = GD::Simple->new(160, 90, 1);
$horizontal->bgcolor('red');
$horizontal->rectangle(10,10,150,80);

my $left = GD::Simple->new(90, 90, 1);
$left->bgcolor('red');
$left->rectangle(10,10,90,80);

my $center = GD::Simple->new(90, 90, 1);
$center->bgcolor('red');
$center->rectangle(0,10,90,80);

my $right = GD::Simple->new(90, 90, 1);
$right->bgcolor('red');
$right->rectangle(0,10,80,80);

my $square = Image::Square->new($horizontal->gd);

my $im_left = $square->square(0, 0);
cmp_ok($im_left->png, 'eq', $left->png, 'left image');

my $im_center = $square->square(0, 0.5);
cmp_ok($im_center->png(5), 'eq', $center->png(5), 'center image');

my $im_right = $square->square(0, 1);
cmp_ok($im_right->png(5), 'eq', $right->png(5), 'right image');

[download]
Drawing a rectangle with a smaller, red rectangle inside it. Then drawing the three parts of this simple shape and comparing them to the output from Image::Square. This works for the left image but not centre or right. Examining the image files, the output from Image::Square is one byte less. Not doubt from copyResampled.

Given your excellent point about libgd and GD::Image being tested, I don't think it is worth me testing the images other than to ensure they are the expected dimensions.

In reply to Re^6: Testing image output by Bod
in thread Testing image output by Bod

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