Test Driven Development

An Introductionby

Lukasz Kujawa

About Me

- Lukasz Kujawa

- Lead Developer at Gloople

- http://systemsarchitect.net/

- @lukaszkujawa

What is TDD?

"Test-driven development (TDD) is a software development process that relies on the repetition of a very short development cycle: first the developer writes an (initially failing) automated test case that defines a desired improvement or new function, then produces the minimum amount of code to pass that test, and finally refactors the new code to acceptable standards"- Wikipedia

What is TDD in English?

Create test before code

TDD Cycle

RED GREEN

REFACTOR

The Three Laws of TDD

- You might not write production code until you have written a failing unit test

- You might not write more of a unit test than is sufficient to fail, and not compiling is failing

- You may not write more production code then is sufficient to pass the currently failing test

TDD Iterations

Test Production code

Write minimal Unit Test Create a Class

Call method of the class Create the Method

Assert output of the method

Add logic to return expected output

Unit Testing

"In computer programming, unit testing is a method by which individual units of source code, sets of one or more computer program modules together with associated control data, usage procedures, and operating procedures, are tested to determine if they are fit for use."- Wikipedia

Unit Testing in English

Testing smallest testable parts of application

Unit Test is not a Test

- Very narrow and well defined scope- No complex dependencies- Test only one application layer- Environment independent- Fast

TTD - Too Damn Difficult?

Benefits for Developer

- Confidence

- Code quality

- Time

- Refactoring

- Reopening issues

- Self documenting code

Benefits for Business

Benefits for Business

- Shorten development cycles

- Delivering more

- Stable products

Research 1

"Art of Unit Testing" by Roy Osherove

Stage Team without tests Team with tests

Implementation (coding)

7 days 14 days

Integration 7 days 2 days

Testing / Bug Fixing 12 days 8 days

Overall release time 26 days 24 days

Bugs in production 71 11

Research 2

Quality improvement through test driven development: results and experiences of four industrial teams (2008) by Nachiappan Nagappan, E. Michael Maximilien, Thirumalesh Bhat and Laurie Williams

http://biblio.gdinwiddie.com/biblio/StudiesOfTestDrivenDevelopment

Research 2Metric description

IBM Drivers Microsoft: Windows

Microsoft: MSN

Microsoft: VS

Defect density of comparable team in organizationbut not using TDD

W X Y Z

Defect density of team using TDD

0.61W 0.38X 0.24Y 0.09Z

Increase in time taken to code the feature becauseof TDD (%)

15-20% 25-35% 15% 20-25%

How to test?<?php

MyFramework::bootstrap();

$obj = new Class_Under_Test();

if( $obj->something('Foo') != 47 ) {throw new Exception('Incorrect output for Foo');

}

if( $obj->someting('Bar') !== false ) {throw new Exception('Incorrect output for Bar');

}

Unit Test Frameworks

- PHPUnit

- SimpleTest

Using Framework

- API

- No maintenance

- Integration with IDE

- Code coverage report

- Mocks

<?php

class MyClassTest extends PHPUnit_Framework_TestCase { public static function setUpBeforeClass() {

MyFramework::initAutoloader(); }

protected function setUp() {$this->myClass = new MyClass();

}

public function testSomething() { $this->assertEquals(1, $this->myClass->something()); }

public function testSomethingElse() { $this->assertTrue( $this->myClass->somethingElse() ); $this->assertFalse $this->myClass->somethingElse( 47 ) ); }

}

PHPUnit - Eclipse integration

Unit Testing - small print

- Can't test directly private, protected and static

methods

- Tests only functionality

- Database

- Requires rigorous discipline

SHOULD I TRY IT?

YESREFACTOR

Q&A