Testing untestable Code - PFCongres 2010

Testing untestable Code
Stephan Hochdörfer, bitExpert AG

"Quality is a function of thought and reflection -
precise thought and reflection. That’s the magic."
Michael Feathers

About me
 Founder of bitExpert AG, Mannheim

 Field of duty

Department Manager of Research Labs

Head of Development for bitFramework

 Focusing on

PHP

Generative Programming


Contact me

@shochdoerfer

S.Hochdoerfer@bitExpert.de

Agenda
1. Theory

2. How to test untestable PHP Code

3. Generate testable code

4. Conclusion

Theory

"There is no secret to writing tests, there
are only secrets to write testable code!"
Miško Hevery

Theory

What is „untestable code“?

Theory

What is „untestable code“?

 Global variables

Singleton

Registry

Globale state
 static method calls
 Control flow in a constructor
 Tight coupling

Dependencies to concrete implementations

to many dependencies to other classes

Dependencies without control

Theory

"...our test strategy requires us to have more control or
visibility of the internal behavior of the system under test."
Gerard Meszaros, xUnit Test Patterns: Refactoring Test Code

Theory

Required
class
Class to
Unittest
Test
Required
class

Theory

Database

Required
class
External
Class to
Unittest resource
test
Required
class

Required Required
Webservice
class class

Theory

How to achieve „testable“ code?

Theory

How to achieve „testable“ code?

Refactoring

Theory

"Before you start refactoring, check that you
have a solid suite of tests."
Martin Fowler, Refactoring

Agenda
1. Theory

2. Testing untestable PHP Code


4. Conclusion

Agenda
1. Theory

2. Testing untestable PHP Code
– Hardcoded Dependencies
– Procedural code
– Overwrite internal PHP functions


4. Conclusion

Testing „untestable“ PHP Code

Assumption

Do not change existing code!

Testing „untestable“ PHP Code | __autoload

<?php
class Car {
private $Engine;

public function __construct($sEngine) {
$this->Engine = Engine::getByType($sEngine);
}

}


<?php
class Car {
private $Engine;

}

}

How to inject a dependency?
 Use __autoload


<?php
function run_autoload($psClass) {
$sFileToInclude = strtolower($psClass).'.php';
if(strtolower($psClass) == 'engine') {
$sFileToInclude = '/custom/mocks/'.$sFileToInclude;
}
include($sFileToInclude);
}

// Testcase
spl_autoload_register('run_autoload');
$oCar = new Car('Diesel');
echo $oCar->run();

Testing „untestable“ PHP Code | include_path

<?php
include('Engine.php');

class Car {
private $Engine;

}
}


<?php
include('Engine.php');

class Car {
private $Engine;

}
}

 Manipulate include_path setting


<?php
ini_set('include_path',
'/custom/mocks/'.PATH_SEPARATOR.
ini_get('include_path'));

// Testcase
include('car.php');

$oCar = new Car('Diesel');
echo $oCar->run();

Testing „untestable“ PHP Code | include_path alternative

<?php
class CustomFileStreamWrapper {
private $_handler;

function stream_open($path, $mode, $options, &$opened_path) {
stream_wrapper_restore('file');
// @TODO: modify $path before fopen
$this->_handler = fopen($path, $mode);
stream_wrapper_unregister('file');
stream_wrapper_register('file', 'CustomFileStreamWrapper');
return true;
}

function stream_read($count) {}

function stream_write($data) {}

function stream_tell() {}

function stream_eof() {}

function stream_seek($offset, $whence) {}
}

stream_wrapper_unregister('file');
stream_wrapper_register('file', 'CustomFileStreamWrapper');

Source: Alex Netkachov, http://www.alexatnet.com/node/203

Testing „untestable“ PHP Code | Namespaces

<?php
class Car {
private $Engine;

$this->Engine = CarEngine::getByType($sEngine);
}
}

Testing „untestable“ PHP Code | Namespaces

<?php
class Car {
private $Engine;

}
}

 Use __autoload or manipulate the include_path

Testing „untestable“ PHP Code | vfsStream

<?php
class Car {
private $Engine;

public function __construct($sEngine, $CacheDir) {
mkdir($CacheDir.'/cache/', 0700, true);
}
}


<?php
class Car {
private $Engine;

public function __construct($sEngine, $CacheDir) {
mkdir($CacheDir.'/cache/', 0700, true);
}
}

How mock a filesystem?
 Use vfsStream - http://code.google.com/p/bovigo/


<?php

// setup vfsStream
vfsStreamWrapper::register();
vfsStreamWrapper::setRoot(new vfsStreamDirectory('app'));

$oCar = new Car('Diesel', vfsStream::url('app'));

echo vfsStreamWrapper::getRoot()->hasChild('cache');

Testing „untestable“ PHP Code

„I have no idea how to unit-test procedural code. Unit-testing
assumes that I can instantiate a piece of my application in
isolation.“
Miško Hevery

Testing „untestable“ PHP Code | Test functions

<?php
function startsWith($sString, $psPre) {
return $psPre == substr($sString, 0, strlen($psPre));
}

function contains($sString, $sSearch) {
return false !== strpos($sString, $sSearch);
}

Testing „untestable“ PHP Code | Test functions

<?php
function startsWith($sString, $psPre) {
return $psPre == substr($sString, 0, strlen($psPre));
}

function contains($sString, $sSearch) {
return false !== strpos($sString, $sSearch);
}

How to test
 PHPUnit can call methods
 PHPUnit can save/restore globale state

Testing „untestable“ PHP Code | overwrite internal functions

<?php
function buyCar(Car $oCar) {
global $oDB;

mysql_query("INSERT INTO...", $oDB);

mail('order@domain.org', 'New sale', '....');
}


<?php
global $oDB;


}

How to test
 Do not load mysql extension. Provide own implementation
 Unfortunatly mail() is part of the PHP core


<?php
global $oDB;


}

How to test
 Use classkit extension to mock internal functions


<?php

ini_set('runkit.internal_override', '1');

runkit_function_redefine('mail','','return true;');

?>

Generate testable code


Configuration

1 ... n
Implementation
Generator Product
components

Generator
application



Configuration

Application

Implementation
Generator
components

Testcases
Generator
application


Course of action
Extraction
 „Mask“ parts of the code

Customizing
 Change content of global vars
 Pre/Postfixes for own functions, methods, classes

Recombine
 Re-order parts of the code


FileFrm FILEIndex_php5 {
private String Prefix = "test_";
private String MailSlot = "mail('order@domain.org', 'New sale', '....');";

public FILEIndex_php5() {
setFilename("index.php5");
setRelativePath("/");
}

private void assign() {
BEGINCONTENT()
<?php
global $oDB;

<!{Prefix}!>mysql_query(„INSERT INTO...“, $oDB);
<!{MailSlot}!>
}

?>
ENDCONTENT()
}
}


1. Example
Prefix: test_
<?php
global $oDB;

test_mysql_query("INSERT INTO...", $oDB);
}


1. Example
Prefix: test_
<?php
global $oDB;

test_mysql_query("INSERT INTO...", $oDB);
}

2. Example
MailSlot: mail('order@domain.org', 'New sale', '....');
<?php
global $oDB;

}

?>

Conclustion

Conclusion

 Change mindset to write testable code

Dependency Injection

 Look for other options to raise the bar

Work around limitations of PHP

PHP is flexible, use it that way

Testing untestable Code - PFCongres 2010

Testing untestable Code - PFCongres 2010

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