A Testing Object for Singleton Pattern written in PHP

singleton.php

<?php
/**
 * Empty Singleton Class
 *
 * @since 2010-09-19
 * @require PHP >= 5.0.0
 */

class Singleton {
  private function __construct() {
  }

  function instance() {
    static $obj;

    if ( !$obj ) {
      $obj = new Singleton();
    }

    return $obj;
  }
}

test_singleton.php

<?php
/**
 * SingletonTestCase
 *
 * @since   2010-09-19
 * @require PHP >= 5.2.0
 */
/** UnitTestCase */
require_once( 'Pearified/Testing/SimpleTest/unit_tester.php' );
/** SimpleReporter */
require_once( 'Pearified/Testing/SimpleTest/reporter.php' );
/** Singleton */
require_once( dirname( __FILE__ ).'/singleton.php' );

class TestingSingleton extends Singleton {
  public function __construct() {
  }

  function instance() {
    return new TestingSingleton();
  }
}

/**
 * SingletonTestCase
 *
 * @since 2010-09-19
 */
class Test_Singleton extends UnitTestCase {
  function Test_Singleton() {
  }

  function test_instance() {
    $obj1 = Singleton::instance();
    $obj2 = Singleton::instance();
    $this->assertEqual( spl_object_hash( $obj1 ), spl_object_hash( $obj2 ) );
  }

  function test_fakeinstance() {
    $this->assertTrue( is_object( new TestingSingleton() ) );
    $obj1 = TestingSingleton::instance();
    $obj2 = TestingSingleton::instance();
    $this->assertFalse( spl_object_hash( $obj1 ) == spl_object_hash( $obj2 ) );
  }

}

if ( realpath( $_SERVER['SCRIPT_FILENAME'] ) == __FILE__ ) {
  $test = new Test_Singleton();
  $reporter = null;
  if ( SimpleReporter::inCli() ) {
    $reporter = new TextReporter();
  } else {
    $reporter = new HtmlReporter();
  }
  exit( $test->run( $reporter ) ? 0 : 1 );
}