Guiding Object-Oriented Design with Tests

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PRESENTED BY JEFF CAROUTH @jcarouth Guiding Object-Oriented Design with Tests

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PRESENTED BY JEFF CAROUTH @jcarouth Guiding Object-Oriented Design with Tests

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“The current fanatical TDD experience leads to a primary focus on the unit tests, because those are the tests capable of driving the code design (the original justiﬁcation for test-ﬁrst).” – DHH http://david.heinemeierhansson.com/2014/tdd-is-dead-long-live-testing.html

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“Is it really surprising that someone who chooses to stuﬀ an entire application’s logic into active record models doesn’t like unit tests?” – me https://twitter.com/jcarouth/status/458963211484557312

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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