I have a different view of TDD. First, use a bare minimum of lines and keep your structures simple at first because you want a minimal skeleton of a test to "fail": Remember to fail first, then write a minimal fix. Take it one small step at a time.

I usually start by writing POD. Put your ideas down in words. Then I use Test::XT. For example, I wrote some POD using some of your ideas:

package Calculator::ForMyExperiment

use strict;
use warnings;

=head1 NAME

Calculator::ForMyExperiment - calculate simple stuff

=head1 VERSION 

version 0.01

=cut

our $VERSION = '0.01';

=head1 SYNOPSIS
    
    use Calculator::ForMyExperiment

    my $data = Calculator::FroMyExperiment->new;
    my $doit = calculate_simple_stuff($experiment);

=head1 DESCRIPTION

    This module has a function for calculating stuff.
    

=head1 EXPORTS

    The calculate_simple_stuff function is exported by default.

=cut

require Exporter;
require DynaLoader;

our (@ISA)       = qw( Exporter DynaLoader);
our (@EXPORT_OK) = qw( calculate_simple_stuff );

bootstrap Calculator::ForMyExperiment $VERSION;

=head1 FUNCTIONS

=head2 calculate_simple_stuff

    Merges simple stuff.

=cut

sub new { 
    my $class = "Calculator::ForMyExperiment"; 
    my %params = @_; 
    my $self = {}; 
    bless $self, $class; 
    return $self; 
}

sub calculate_simple_stuff {
    my($stuff) = qw/one two three/; 
    foreach $stuff( my @stuffing ) {
        $stuff = shift();
        print $stuff;
}

1;
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Now use Test::XT to write a test for pod syntax:

#!/usr/bin/perl

use strict;
use warnings;
use Test::XT 'WriteXT';

my $test = Test::XT->new(
    test    => 'all_pod_files_ok',
    release => 0,
    comment => 'Test that the syntax of the POD documentation is valid
+',
    modules => {
        'Pod::Simple' => 0,
        'Test::Pod'   => 0,
    },
    default => 't/pod.t',
);

$test->module( 'Spreadsheet::WriteExcel' );
$test->test( 'all_pod_coverage_ok' );

print "Test script: ";
print $test->write_string;
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The resulting output:

#!/usr/bin/perl -l

# Test that the syntax of the POD documentaion is valid
use strict;
BEGIN {
    $|  = 1;
    $^W = 1;
}

my @MODULES = (
    'Pod::Simple' => 0,
    'Test::Pod'   => 0,
    'Spreadsheet::WriteExcel" => 0,
   
);

# Don't run tests during end-user installs
use Test::More;
plan( skip_all => 'Author tests not required for installation' )
  unless ( $ENV{RELEASE_TESTING} or $ENV{AUTOMATED_TESTING} );

# Load the testing modules
foreach my $MODULE ( @MODULES ) {
    eval "use $MODULE";
    if ( $@ ) {
    $ENV{RELEASE_TESTING}
    ? die( "Failed to load required release-testing module $MODULE" )
    : plan( skip_all => "$MODULE not available for testing" );
    }
}

all_pod_coverage_ok();

1;
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Now you're good to go!