Gurus Place

Value Design Pattern

October 22, 2006 on 4:00 am | In Design Patterns, PHP | No Comments

Sometimes while you are coding, you need some kind of a wrap for some primitive data type such as an integer, just to add some feature that is not available directly from that primitive data type, or just to give it some identity.
A Date, Integer, or Dollar class is a handy - and inexpensive - encapsulation, easily copied, compared, or created when needed.
For example managing Bytes and printing them can be something annoying, for example, when ever you need to print the number of Bytes in a file, you would like to check if it can be represented in KB, MB, or GB.
So what I’m going to do here is to wrap the integer datatype into a Byte class, and override it’s __toString function (one of the magic functions in PHP 5) so every time time I need to print it a simple print would do the issue.
Our example here would be for a mailbox, every mailbox has a quota, I want to give it a starting quota, then increase it, so first I’m going to write the Test for it (Using simpletest).

<?php
// …. includes and stuff
class TestByte extends UnitTestCase {
  function testQuotaByte () {
    $this->>UnitTestCase(”Test Byte Value”);
    $startingQuota = new Byte(1048576); // One Mega
    $mailbox1 = new MailBox($startingQuota);
    $mailbox2 = new MailBox($startingQuota);
    $this->assertEqual(1048576,$mailbox1->getQuota()->getBytes());
    $this->assertEqual(1048576,$mailbox2->getQuota()->getBytes());
    $mailbox1->increaseQuotaBy(new Byte(524288)); // add 512KB
    $this->assertEqual(1572864,$mailbox1->getQuota()->getBytes());
    $this->assertEqual(1048576,$mailbox2->getQuota()->getBytes());
    $this->assertEqual(1048576,$startingQuota->getBytes());
  }
}

$test = new TestByte();
$test->run(new HtmlReporter());
?>

Here I created to Mailboxes, and gave them a starting quota of 1 MB, after that I added 512 KB to one of them, and checked that it was added, and that the other mailbox and starting Quota was not changed.
Let’s start with the implementation:

<?php
class Byte {
  protected $amount;
  protected static $Names = array(”B” => “B”,
      ’KB’ => ‘KB’,
      ’MB’ => ‘MB’,
      ’GB’ => ‘GB’,
      ’TB’ => ‘TB’);

  function __construct($bytes) {
    $this-$gt;amount = $bytes;
  }

  public function add(Byte $bytes) {
    $this->amount += $bytes->getBytes();
  }

  public function getBytes() {
    return $this->amount;
  }

  public function getKB () {
    return $this->amount/1024;
  }

  public function getMB () {
    return $this->amount/1048576;
  }

  public function getGB() {
    return $this->amount/1073741824;
  }

  public function getTB() {
    return $this->amount/1099511627776;
  }

  public function __toString() {
    if($this->getTB() >= 1) {
      return number_format($this->getTB(), 2, ‘.’, ‘ ‘)." ".self::$Names['TB'];
    } elseif ($this->getGB() >= 1) {
      return number_format($this->getGB(), 2, ‘.’, ‘ ‘)." ".self::$Names['GB'];
    } elseif ($this->getMB() >= 1) {
      return number_format($this->getMB(), 2, ‘.’, ‘ ‘)." ".self::$Names['MB'];
    } elseif ($this->getKB() >= 1) {
      return number_format($this->getKB(), 2, ‘.’, ‘ ‘)." ".self::$Names['KB'];
    } else {
      return "$this->amount ".self::$Names['B'];
    }
  }
}
?>

and The Simple MailBox :

<?php
class MailBox {
  protected $quota;

  function __construct(Byte $quota) {
    $this->quota = $quota;
  }

  public function getQuota() {
    return $this->quota;
  }

  public function increaseQuotaBy(Byte $addedQuota) {
    $this->quota->add($addedQuota);
  }
}
?>

OK Let’s run the test.

TestByte
Fail: testQuotaByte -> Equal expectation fails because [Integer: 1048576] differs from [Integer: 1572864] by 524288 at [/some/Location/TestByte.php line 19]
Fail: testQuotaByte -> Equal expectation fails because [Integer: 1048576] differs from [Integer: 1572864] by 524288 at [/some/Location/TestByte.php line 21]
1/1 test cases complete: 3 passes, 2 fails and 0 exceptions.

What happened here? this code now points to ($this->assertEqual(1048576,$mailbox2->getQuota()->getBytes());) and ($this->assertEqual(1048576,$startingQuota->getBytes());) lines, Any Idea?
Here is a hint: in PHP 5 Objects are passed By Handle (Something like reference, yes similar to Java) not by value, is it clear now?
Another hint: They all point to the same Byte Object.
So actually changing one of them is changing them all.
So, how do you implement a lightweight, or easy to construct, descriptive object like Byte?

Lightweight objects should behave like PHP integers: if you assign the same object to two different variables and then change one of the variables, the other variable should remain unaffected. And indeed this is the goal of the Value Object pattern.So now we need to make the Byte Object immutable (i.e does not change once it’s been set).

OK it’s so Simple in our example, for the Byte class we change the add function to

<?php
//…
  public function add(Byte $bytes) {
    return new Byte($this->amount + $bytes->getBytes());
  }
//…
?>

also remember to change the MailBox class increaseQuotaBy function as now $quota is not changed in the add operation

<?php
//…
  public function increaseQuotaBy(Byte $addedQuota) {
    $this->quota = $this->quota->add($addedQuota);
  }
//…
?>

running the test

TestByte
1/1 test cases complete: 5 passes, 0 fails and 0 exceptions.

Viola!!, everything is cool.
Hope this article was useful, once again if you have ant question, don’t hesitate to comment

Testing your code

October 21, 2006 on 7:50 am | In PHP | No Comments

Perhaps no other coding practice is as important as testing your code. Also in the nature of Business Development, where parts of your code always change on the request of a client (including Management), or even when you want to make your code run with better performance, Automated tests are highly needed, you can’t just spread your print statements all over your code every time you need to test it.
With automated tests, you can just be sure that your interface is not broken after some change, you just run your tests, if they succeed, you know that you didn’t break your code (this means you should right good tests).
Let’s start by a simple example, Imagine that we have been asked to test PHP’s built-in Array. One bit of functionality to test is the function sizeof(). For a newly created array we expect the sizeof() function to return 0. After we add an element, sizeof() should return 1. (I know it’s not a big deal, but it’s just an example).
you can do it with simple print statements (i.e. print (1 == sizeof($myArray) ? "OK":"Failure").PHP_EOL; ), but here we are going to do it by using an assertion function.

<?php
$fixture = Array();
assertTrue(sizeof($fixture) == 0);

$fixture[] = "element";
assertTrue(sizeof($fixture) == 1);

function assertTrue($condition) {
  if (!$condition) {
    throw new Exception("Assertion failed.");
  }
}
?>

Well, we could know if something went wrong if some Exception was raised, of course assertTrue is not the only thing you want to do, UnitTesting has gone far beyond that, usually UnitTesting frameworks provide a whole lot of features that you need for your testing.
Lot’s of Testing frameworks are available for PHP, I’m going to point to 2 of them, the first one is SimpleTest (http://simpletest.org/), it’s written in PHP 4 (Although they are going to migrate to PHP 5 when they reach version 2), so you can use it on both PHP 4 and 5 programs, also it includes a nice HTML reporter for some good looking html results the same test above could be written using this framework as:

<?php
require_once ’simpletest/unit_tester.php’;
require_once ’simpletest/reporter.php’;

class TestingFixtureArray extends UnitTestCase {
  function TestArray() {
    $this->UnitTestCase("Testing Fixture Array");
    $fixture = Array();
    $this->assertTrue(sizeof($fixture) == 0);

    $fixture[] = "element";
    $this->assertTrue(sizeof($fixture) == 1);
  }
}

//run the Test
$test = new TestingFixtureArray();
$test->run(new HtmlReporter());
?>

Another Well know testing framework is known as PHPUnit2 (http://www.phpunit.de/), it’s available through the PEAR Repository, you can install it as
$ pear install PHPUnit2
It’s written in PHP 5, and is so widely used within PHP Developers, a good resource for learning how to use it is the free available online book PHPUnit Pocket Guide (http://www.phpunit.de/pocket_guide/index.en.php), the same example could be:

<?php
require_once ‘PHPUnit2/Framework/TestCase.php’;

class ArrayTest extends PHPUnit2_Framework_TestCase {
  public function testNewArrayIsEmpty() {
    // Create the Array fixture.
    $fixture = Array();

    // Assert that the size of the Array fixture is 0.
    $this->assertEquals(0, sizeof($fixture));
  }

  public function testArrayContainsAnElement() {
    // Create the Array fixture.
    $fixture = Array();

    // Add an element to the Array fixture.
    $fixture[] = ‘Element’;

    // Assert that the size of the Array fixture is 1.
    $this->assertEquals(1, sizeof($fixture));
  }
}
?>

and you can run it on command line as
$ phpunit ArrayTest

Additional benefits that you can realize by thoroughly testing your code:

Testing forces you to write code that is easily testable. This leads to looser coupling, flexible designs, and good modularity.
Writing tests forces you to explicitly clarify your expectations of how your code is to behave, distilling your design into sharper focus from the beginning. Writing tests forces you to consider the universe of possible inputs and the corresponding results.
Tests are very explicit way of communicating the intent of your code. In other words, test cases act as example and documentation, showing exactly how a given class, method, or function should behave. A test case defines how code works in a non-ambiguous way.

Finally, if your test suite - your set of test cases - is very thorough, you can say your code is complete when all of your test pass. Interestingly, that notion is one of the hallmarks of Test Driven Development.
Test Driven Development (TDD), also referred to as Test First Coding, is a methodology that takes testing one step further: you write your tests before you ever write any code. A nice, brief summary of the tenants of TDD is available at http://xprogramming.com/xpmag/testFirstGuidelines.htm, and a good introductory book on the strategy is “Test Driven Development: By Example” by Kent Beck. (The book’s examples are in Java, but it’s a quick read and gives you a very good overview and introduction to the subject.)

Agile Development
Recently, unit testing - in particular Test Driven Development - has been associated with agile Development methodologies such as Extreme Programming (XP)g that focus on rapid iterations of releasing functional code to customers and welcoming changing customer requirements as a natural part of the development process. Some good online resources for learning about agile development include:

if you have any question regarding this post, just drop a comment, and I would be more than happy to answer (if I could :P)