Untestable Code

Untestable Code Sebastian Bergmann November 28th 2009

Sebastian Bergmann  Co-Founder and Principal Consultant with thePHP.cc  Creator of PHPUnit  Involved in the PHP project since 2000

Throwaway code (sometimes) has a right to exist. But this is not what we are dicussing here today.

It is okay to never test code that never changes. For everything else, you need tests. (Timothy Fitz)

We are interested in code that is to be maintained over a long period of time.

Spaghetti Code is unmaintainable.

Spaghetti Code is untestable.

Separation of Concerns Concerns should be implemented separate from each other.

Separation of Concerns Concerns should be implemented as decoupled components.

Separation of Concerns Design Patterns help decouple concerns.

Stop! This is not a presentation about architecture!

Back to the code, then.

What makes code untestable? Most people say Real issues  Make things private  Mix new with logic  Use final keyword  Look for things  Write long methods  Work in constructor  ...  Singletons  Global state  Static methods This slide contains material by Miško Hevery

Constructor Issues <?php Mixing object graph class Document { construction with work private $html; public function __construct($url) { $client = new HttpClient; $this->html = $client->get($url); } } ?> Doing work in the constructor This slide contains material by Miško Hevery

Constructor Issues <?php class Document { private $html; public function __construct($url) { $client = new HttpClient; $this->html = $client->get($url); } } ?> A Document object cannot be isolated from its dependency on an HttpClient object as we cannot pass a Test Double to the constructor This slide contains material by Miško Hevery

Solving the design problem Step 1: Do not mix new with logic <?php class Document { private $html; public function __construct(HttpClient $client, $url) { $this->html = $client->get($url); } } ?> Doing work in the constructor This slide contains material by Miško Hevery

Interlude Test Doubles Replacing a component on which the tested component depends with a "test-specific equivalent". <?php class DocumentTest extends PHPUnit_Framework_TestCase { public function testSomething() { $stub = $this->getMock('HttpClient'); $stub->expects($this->any()) ->method('get') ->will($this->returnValue('<html>...</html>')); $document = new Document($stub, 'url'); // ... } } ?>

Solving the design problem Step 2: Do not perform work in the constructor <?php class Document { private $html; public function __construct($html) { $this->html = $html; } } This slide contains material by Miško Hevery

Solving the design problem Step 2: Do not perform work in the constructor <?php class Document { private $html; public function __construct($html) { $this->html = $html; } } class DocumentFactory { public function __construct(HttpClient $client) { $this->client = $client; } public function build($url) { return new Document($this->client->get($url)); } } This slide contains material by Miško Hevery

Global State  Global variables  Static variables in classes  Static variables in functions and methods  Persistent Data  Database  Filesystem  Distributed Data  memcached

Global State Global Variables and PHPUnit  Default Behaviour  Backup $GLOBALS before the execution of a test  Run the test  Restore $GLOBALS after the execution of a test  $backupGlobals = FALSE  Do not backup and restore $GLOBALS  $backupGlobalsBlacklist = array()  Backup and restore $GLOBALS but not the variables listed in the array

Lets look at a real world example. Show Me The Code!

Habari superglobal.php (revision 3563) 11 class SuperGlobal extends ArrayIterator 12 { 29 public static function process_gps() 30 { 44 $_GET = new SuperGlobal($_GET); 45 $_POST = new SuperGlobal($_POST); 46 $_SERVER = new SuperGlobal($_SERVER); 47 unset($_REQUEST); 50 } 263 }  It is not possible to test this code without populating the actual superglobals first  Why not pass them as a parameter so you can easily "simulate" input when testing?

Singletons are global state, too.

Global State Static Attributes and PHPUnit <?php class Singleton { private static $uniqueInstance = NULL; protected function __construct() {} private final function __clone() {} public static function getInstance() { if (self::$uniqueInstance === NULL) { self::$uniqueInstance = new Singleton; } return self::$uniqueInstance; } } ?>

Global State Static Attributes and PHPUnit  Default Behaviour  Do not backup/restore static attributes  --static-backup  $backupStaticAttributes = FALSE  Do not backup and restore static attributes  $backupStaticAttributesBlacklist = array()  Backup and restore static attributes but not the ones listed in the array

”Static methods are death to testability.” - Miško Hevery

Testable Code ”The secret in testing is in writing testable code” Miško Hevery

Avoid the hell that is global state.

Use loosely coupled objects …

Use loosely coupled objects … … and dependency injection to wire them together.

Write short methods.

Maybe this presentation was about architecture after all …

The End Thank you for your interest! These slides will be posted on http://slideshare.net/sebastian_bergmann I am co-authoring a book on Quality Assurance in PHP Projects http://phpqabook.com/

License This presentation material is published under the Attribution-Share Alike 3.0 Unported license. You are free: ✔ to Share – to copy, distribute and transmit the work. ✔ to Remix – to adapt the work. Under the following conditions: ● Attribution. You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). ● Share Alike. If you alter, transform, or build upon this work, you may distribute the resulting work only under the same, similar or a compatible license. For any reuse or distribution, you must make clear to others the license terms of this work. Any of the above conditions can be waived if you get permission from the copyright holder. Nothing in this license impairs or restricts the author's moral rights.

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Untestable Code

by Sebastian Bergmann on Nov 29, 2009

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Untestable Code — Presentation Transcript