Guiding Object-Oriented Design with Tests

A test suite is a very useful tool in any application. Often times people refer to unit test suites as a safety net for refactoring and modification. While that is one benefit of having a comprehensive testing strategy and implementation, the real power of unit testing comes when you learn to allow the tests you are writing to inform the design of your application. In this session we will explore the why and how of writing tests for code architecture and object-oriented design purposes. We will follow the path of designing objects within a realistic problem domain.

Transcript

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

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

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3. “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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4. “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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5. Why Test?
   1.
   

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6. Software Development
   Learning
   Feedback
   the process of
   requires
   which requires
   

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7. Traditional
   Development
   

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8. 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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9. 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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10. OOP/OOD
    2.
    

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11. !
    Communication
    over
    implementation
    

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

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

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14. TDD & OOP
    3.
    

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15. The Problem
    

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

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17. ! 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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18. namespace Example;!
    class Cart!
    {!
    public function count()!
    {!
    return 0;!
    }!
    }!
    

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

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21. 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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22. ! 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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23. class Cart!
    {!
    //...snip...!
    public function addProduct($product)!
    {!
    !
    }!
    }!
    namespace Example;!
    class Product!
    {!
    !
    }!
    

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

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26. ! 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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27. 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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28. ! 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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29. 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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30. 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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31. ! 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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32. 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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33. 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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34. ! 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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35. class Cart implements \Countable!
    {!
    //...snip...!
    }!
    

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36. ! 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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37. 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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38. 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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39. 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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40. class Cart implements \Countable!
    {!
    //...snip...!
    !
    public function subtotal()!
    {!
    $runningTotal = 0;!
    foreach ($this->contents as $product) {!
    $runningTotal += $product->getPrice();!
    }!
    return $runningTotal;!
    }!
    }!
    

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

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42. ! 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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43. But...Unit Tests
    

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44. 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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45. 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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46. But...interfaces
    

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47. But...interfaces
    roles
    

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48. 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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49. 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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50. namespace Example;!
    interface Sellable!
    {!
    public function getPrice();!
    }!
    

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51. ! 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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52. 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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53. 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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54. ! 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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55. 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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56. 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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57. Tip
    Type Hint on Roles Rather than Implementations
    public function addProduct(Sellable $product)!
    {!
    $this->contents[] = $product;!
    }!
    

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

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59. 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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60. 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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61. ! 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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62. You can mock nonexistent
    interfaces to help you design the
    collaborators your object will use.
    Takeaway #4
    

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63. Recap
    4.
    

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64. Tests are
    sandboxes
    for your objects
    

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65. Focus on
    Communication
    

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66. Listen to
    your tests
    and refactor
    

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67. Further Reading
    

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

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69. Thank You
    @jcarouth
    joind.in/10825
    

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