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Architecture and testability Listen to your tests on steroids Giorgio Sironi

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Who I am <ul><li>PHP freelancer from 2005, software architect @ Allbus

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Writer for DZone[, php|architect]

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Bachelor of Computer Engineering @ PoliMi cum laude </li></ul>

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This talk <ul><li>Maintainability, and why testing

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Various techniques to favor ease of testing AND maintainability </li></ul>

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What is maintainability? <ul><li>Being ready to change!

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…but not too much

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Taking the first bullet </li></ul>

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Favored by maintainability <ul><li>New requirements

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Evolving requirements

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Iterative development (Agile)

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Long-term maintenance </li></ul>

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Kinds of tests <ul><li>Unit tests (1 object)

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Functional tests (N objects), end-to-end tests (All objects)

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Integration tests (external resources) </li></ul>

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Maintainability (1 of 2) <ul>SOLID principles (not all of them) <li>Single responsibility

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Open/closed

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Dependency Inversion </li></ul>

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Maintainability (2 of 2) <ul>Loose coupling High cohesion Information hiding ...needed from day 1, like readability and testability </ul>

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<ul>That was the boring part... </ul>

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Good but... <ul>Good buzzwords, but how do I apply that in practice? </ul>

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Testing first <ul><li>Testing first -> Testable code

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Testable code -> Maintainable code

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Maintainable code -> Happy programmer </li></ul>

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Problems with tests <ul><li>A test is slow?

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A test is brittle?

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A test is difficult to write? </li></ul>

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Solution to problems with tests <ul>Change the design to ease testing ( listen to your tests ) </ul>

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Examples of listening to the tests <ul><li>Small tests => high cohesion

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Unit tests => loose coupling

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Fast tests => in-memory isolation

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4 pillars... </li></ul>

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1. Dependency injection <ul><li>No new operators outside of Factories

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Easy to change lifecycles and implementations </li></ul>

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1. Dependency Injection (without) <?php class Ferrari { private $engine ; public function __construct () { $this ->engine = new Engine (); } }

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1. Dependency Injection (with) <?php class Ferrari { private $engine ; public function __construct (Engine $engine ) { $this ->engine = $engine ; } }

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2. Avoid static methods <ul><li>Explicit concepts as objects

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Orthogonality of collaboration </li></ul>

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2. Avoid static methods (before) <?php class Collection { public function find ( $key ) { Sorter:: sort ( $this ); // ..search stuff } }

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2. Avoid using static methods (after) <?php class Collection { public function find ( $key ) { $this ->sorter-> sort ( $this ); // ..search stuff } }

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3. Law of Demeter <ul><li>Do not walk the... arrows

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Or: don't talk to strangers </li></ul>

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3. Law of Demeter (without) <?php class PC { public function powerOn () { $this ->mobo->cpu->cache -> powerOn (); } }

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3. Law of Demeter (with) <?php class PC { public function powerOn () { foreach ( $this ->powered as $item ) { /** @var Powered $item */ $item -> powerOn (); } } }

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3. Law of Demeter (with) <?php class PC { public function powerOn () { $this ->mobo-> powerOn (); } }

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4. Singleton vs. Factory <ul><li>A Singleton is hard to mock

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Hidden dependency

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Global state </li></ul>

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4. Singleton vs. Factory <?php class Authenticator { public function login ( $user , $pass ) { Db:: select (...); } }

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4. Singleton vs. Factory <?php class Authenticator { public function __construct (Db $db ) { ... } public function login ( $user , $pass ) { $this ->db-> select (...); } }

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Be honest <ul><li>If you need something, inject it (or inject its factory)

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Telling is better than looking around

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Tests are a recipe for clean code </li></ul>

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TDD is... <ul>Test-Driven Development Design </ul>

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References <ul><li>Guide: Writing Testable Code (Misko Hevery)

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Growing Object-Oriented Software, Guided by Tests – Freeman, Price #goos </li></ul>

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Contacts <ul><li>Personal blog: http://giorgiosironi.blogspot.com

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On Twitter: @giorgiosironi </li></ul>

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Questions? Q/A