Dependency Injectionを特定のDIコンテナに頼らず実現する ref: http://qiita.com/Hiraku/items/48fbdfca4b63c74494e9

di.php

<?php
$container = new \Pimple();

// オブジェクトコンストラクションのコンフィギュレーション
$container['infrastructure.mailer'] = function($container) {
    $mailer = new \SendmailMailer();

    return $mailer;
};
$container['domain.transfer.newsletter'] = function($container) {
    $newsletterTransfer = new \NewsletterTransfer($container['infrastructure.mailer']);

    return $newsletterTransfer;
};

return $container;

example.php

<?php
$container = new FactoryDefault;
// オブジェクトの利用
$newsletterTransfer = $container->createDomainTransferNewsletter();
$newsletterTransfer->send('ニュースレター本文');

FactoryDefault.php

<?php
class FactoryDefault
{
  function createInfrastructureMailer()
  {
    return new SendmailMailer;
  }

  function createDomainTransferNewsletter()
  {
    return new NewsletterTransfer($this->createInfrastructureMailer());
  }
}

FactoryTest.php

<?php
class FactoryTest extends FactoryDefault
{
  function createInfrastructureMailer()
  {
    return new SendmailMailerMock;
  }
}

file3.php

  function createInfrastructureMailer()
  {
    static $mailer;
    return $mailer ?: ($mailer = new SendmailMailer);
  }

file6.php

//...
  function createInfrastructureMailer()
  {
    $mailer = parent::createInfrastructureMailer();
    $mailer->setOption('hogehoge');
    return $mailer;
  }
//...

test.php

<?php
$container = new FactoryTest; //こっちに差し替える
//...