Guiding Object-Oriented Design with Tests

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Guiding Object-Oriented Design with Tests Jeff Carouth // @jcarouth

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Why Test? 1.

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Software Development Learning Feedback the process of requires which requires

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Traditional Development

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Unit Testing in the context of object-oriented design helps us clarify what our objects are supposed to do and how they collaborate to accomplish that goal.

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Testing, speciﬁcally unit testing, aids our goals of using object-oriented programming techniques by giving us the feedback loop we need to inform our design. Takeaway #1

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OOP/OOD 2.

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Communication over implementation

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Value code that is easier to maintain over code that is easier to write.

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Unit testing helps us by allowing us to focus on established best practices of OOP/D. Takeaway #2

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TDD & OOP 3.

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The Problem

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class CartTest extends \PHPUnit_Framework_TestCase { public function testCartIsInitiallyEmpty() { $cart = new \Example\Cart(); $this->assertEquals(0, $cart->count()); } }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist F Fatal error: Class 'Example\Cart' not found

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namespace Example; class Cart { public function count() { return 0; } }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist . Time: 422 ms, Memory: 4.00Mb OK (1 test, 1 assertion)

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Business Requirement A customer should be able to add products to his or her cart.

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class CartTest extends \PHPUnit_Framework_TestCase { //...snip... public function testCanAddOneProductToCart() { $cart = new \Example\Cart(); $cart->addProduct(new \Example\Product()); $this->assertEquals(1, $cart->count()); } }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist F Fatal error: Call to undefined method Example\Cart::addProduct() Fatal error: Class 'Example\Product' not found

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class Cart { //...snip... public function addProduct($product) { } } namespace Example; class Product { }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist .F Time: 56 ms, Memory: 4.00Mb There was 1 failure: 1) CartTest::testCanAddOneProductToCart Failed asserting that 0 matches expected 1. /projects/testing-ood/tests/Example/CartTest.php:16 FAILURES! Tests: 2, Assertions: 2, Failures: 1.

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class Cart { private $contents; public function __construct() { $this->contents = array(); } //...snip... public function addProduct($product) { $this->contents[] = $product; } }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist .F Time: 48 ms, Memory: 4.00Mb There was 1 failure: 1) CartTest::testCanAddOneProductToCart Failed asserting that 0 matches expected 1. /projects/testing-ood/tests/Example/CartTest.php:16 FAILURES! Tests: 2, Assertions: 2, Failures: 1.

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class Cart { private $contents; public function __construct() { $this->contents = array(); } public function count() { return count($this->contents); } public function addProduct($product) { $this->contents[] = $product; } }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist .. Time: 48 ms, Memory: 4.00Mb OK (2 tests, 2 assertions)

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class CartTest extends \PHPUnit_Framework_TestCase { public function testCartIsInitiallyEmpty() { $cart = new \Example\Cart(); $this->assertEquals(0, $cart->count()); } public function testCanAddOneProductToCart() { $cart = new \Example\Cart(); $cart->addProduct(new \Example\Product()); $this->assertEquals(1, $cart->count()); } }

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class CartTest extends \PHPUnit_Framework_TestCase { public function setUp() { $this->cart = new \Example\Cart(); } public function tearDown() { $this->cart = null; } public function testCartIsInitiallyEmpty() { $this->assertEquals(0, $this->cart->count()); } public function testCanAddOneProductToCart() { $this->cart->addProduct(new \Example\Product()); $this->assertEquals(1, $this->cart->count()); } }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist .. Time: 47 ms, Memory: 4.00Mb OK (2 tests, 2 assertions)

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class CartTest extends \PHPUnit_Framework_TestCase { //...snip... public function testCartImplementsCountable() { $this->assertInstanceOf('Countable', $this->cart); } public function testCartIsInitiallyEmpty() { $this->assertEquals(0, count($this->cart)); } public function testCanAddOneProductToCart() { $this->cart->addProduct(new \Example\Product()); $this->assertEquals(1, count($this->cart)); } }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist FF. Time: 94 ms, Memory: 3.75Mb There were 2 failures: 1) CartTest::testCartImplementsCountable Failed asserting that Example\Cart Object (...) is an instance of class "Countable". /projects/testing-ood/tests/Example/CartTest.php:18 2) CartTest::testCartIsInitiallyEmpty Failed asserting that 1 matches expected 0. /projects/testing-ood/tests/Example/CartTest.php:23 FAILURES! Tests: 3, Assertions: 3, Failures: 2.

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class Cart implements \Countable { //...snip... }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist ... Time: 47 ms, Memory: 3.75Mb OK (3 tests, 3 assertions)

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Use the tests cases you write to document your code’s behavior and roles for other developers–including your future self. Takeaway #3

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Business Requirement The subtotal for any given purchase is equivalent to the sum of the products’ prices in a customer’s cart.

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class CartTest extends \PHPUnit_Framework_TestCase { //...snip... public function testSubtotalSumsAllProductsInCart() { $this->cart->addProduct(new \Example\Product(2000)); $this->cart->addProduct(new \Example\Product(1500)); $this->assertEquals(3500, $this->cart->subtotal()); } }

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class Cart implements \Countable { //...snip... public function subtotal() { $runningTotal = 0; foreach ($this->contents as $product) { $runningTotal += $product->getPrice(); } return $runningTotal; } }

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class Product { private $price; public function __construct($price = 0) { $this->price = $price; } public function getPrice() { return $this->price; } }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist .... Time: 51 ms, Memory: 3.75Mb OK (4 tests, 4 assertions)

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But...Unit Tests

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class CartTest extends \PHPUnit_Framework_TestCase { //...snip... public function testSubtotalSumsAllProductsInCart() { $productOne = $this->getMockBuilder('\\Example\\Product') ->setMethods(array('getPrice')) ->getMock(); $productOne->expects($this->once()) ->method('getPrice') ->will($this->returnValue(2000)); $productTwo = $this->getMockBuilder('\\Example\\Product') ->setMethods(array('getPrice')) ->getMock(); $productTwo->expects($this->once()) ->method('getPrice') ->will($this->returnValue(1500)); $this->cart->addProduct($productOne); $this->cart->addProduct($productTwo); $this->assertEquals(3500, $this->cart->subtotal()); } }

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Tip You can mock interfaces that do not exist class InterfaceDoesNotExistTest extends \PHPUnit_Framework_TestCase { public function testItDoesNotExistLOL() { $mock = $this->getMockBuilder('\\My\\NonExistentInterface') ->setMethods(['lolForReal']) ->getMock(); $mock->expects($this->once()) ->method('lolForReal') ->will($this->returnValue('LOL')); $this->assertEquals('LOL', $mock->lolForReal()); } }

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But...interfaces

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But...interfaces roles

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class CartTest extends \PHPUnit_Framework_TestCase { //...snip... public function testSubtotalSumsAllProductsInCart() { $productOne = $this->getMockBuilder('\\Example\\Sellable') ->getMock(); $productOne->expects($this->once()) ->method('getPrice') ->will($this->returnValue(2000)); $productTwo = $this->getMockBuilder('\\Example\\Sellable') ->getMock(); $productTwo->expects($this->once()) ->method('getPrice') ->will($this->returnValue(1500)); $this->cart->addProduct($productOne); $this->cart->addProduct($productTwo); $this->assertEquals(3500, $this->cart->subtotal()); } }

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namespace Example; interface Sellable { public function getPrice(); }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist .... Time: 68 ms, Memory: 3.75Mb OK (4 tests, 6 assertions)

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class CartTest extends \PHPUnit_Framework_TestCase { //...snip... public function testSubtotalSumsAllProductsInCart() { $this->cart->addProduct($this->product(2000)); $this->cart->addProduct($this->product(1500)); $this->assertEquals(3500, $this->cart->subtotal()); } private function product($price = 0, $expectPrice = true) { $product = $this->getMockBuilder('\\Example\\Sellable') ->getMock(); if ($expectPrice) { $product->expects($this->once()) ->method('getPrice') ->will($this->returnValue($price)); } return $product; } }

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class CartTest extends \PHPUnit_Framework_TestCase { //...snip... public function testCanAddOneProductToCart() { $this->cart->addProduct($this->product(500, false)); $this->assertEquals(1, count($this->cart)); } //...snip... }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist .... Time: 66 ms, Memory: 3.75Mb OK (4 tests, 6 assertions)

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class CartTest extends \PHPUnit_Framework_TestCase { public function testCartImplementsCountable() { $this->assertInstanceOf('Countable', $this->cart); } public function testCartIsInitiallyEmpty() { $this->assertEquals(0, count($this->cart)); } public function testCanAddOneProductToCart() { $this->cart->addProduct($this->product(500, false)); $this->assertEquals(1, count($this->cart)); } public function testSubtotalSumsAllProductsInCart() { $this->cart->addProduct($this->product(2000)); $this->cart->addProduct($this->product(1500)); $this->assertEquals(3500, $this->cart->subtotal()); } }

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namespace Example; class Cart implements \Countable { public function count() { return count($this->contents); } public function addProduct(Sellable $product) { $this->contents[] = $product; } public function subtotal() { $runningTotal = 0; foreach ($this->contents as $product) { $runningTotal += $product->getPrice(); } return $runningTotal; } }

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Tip Type Hint on Roles Rather than Implementations public function addProduct(Sellable $product) { $this->contents[] = $product; }

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Business Requirement Promotions are allowed to be applied to a cart but can only apply to certain types of products.

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class CartTest extends \PHPUnit_Framework_TestCase { public function testPromotionSubtractsAmountFromTotal() { $this->cart->addProduct($this->product(2000)); $this->cart->addProduct($this->book(1000)); $bookPromotion = $this->getMockBuilder('\\Example\\Promotion') ->setMethods(array('applyTo')) ->getMock(); $bookPromotion->expects($this->any()) ->method('applyTo') ->will($this->returnCallback(function($product) { if ($product->getType() == 'Book') { return $product->getPrice() * 0.9; } return $product->getPrice(); })); $this->cart->setPromotion($bookPromotion); $this->assertEquals(2900, $this->cart->total()); } }

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class Cart implements \Countable { //...snip... public function setPromotion(Promotion $promo) { $this->promotion = $promo; } public function total() { $runningTotal = 0; foreach ($this->contents as $product) { if ($this->promotion !== null) { $runningTotal += $this->promotion->applyTo($product); } else { $runningTotal += $product->getPrice(); } } return $runningTotal; } }

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! phpunit tests/Example/CartTest.php PHPUnit 3.7.28 by Sebastian Bergmann. Configuration read from /projects/testing-ood/phpunit.xml.dist ..... Time: 92 ms, Memory: 3.75Mb OK (5 tests, 11 assertions)

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You can mock nonexistent interfaces to help you design the collaborators your object will use. Takeaway #4

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Recap 4.

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Tests are sandboxes for your objects

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Focus on Communication

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Listen to your tests and refactor

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http://crth.net/testing-ood Example code

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JEFF CAROUTH DEVELOPER AT LIFTOPIA @jcarouth [email protected] Freenode: #phpmentoring