Replacing dependents with doubles is a central part of testing that every developer has to master. This talk goes over the different types of doubles and explains their place in testing, how to implement them in a mainstream mocking framework, and which strategies or doubles to use in different message exchange scenarios between objects. After this talk you will have moved a step forward in your understanding of testing in the context of object oriented programming.

1. Mocking
Demystified
by @_md

2. how many of you
write tests?

3. how many
write tests before the code?

4. how many of you
know what a mock is?

5. how many of you use mocks?

6. ALL YOU NEED TO KNOW ABOUT TESTING
(in 5 minutes)

7. test
Arrange
Act
Assert

8. test
instantiate
Arrange
tested object
Act
Assert

9. instantiate
Arrange
tested object
$parser = new MarkdownParser;

10. test
Arrange
run the method
Act you want to test
Assert

11. run the method
Act
you want to test
$parser = new MarkdownParser;
$html = $parser->toHtml('Hello World');

12. test
Arrange
Act
Assert specify the
expected outcome

13. specify the
Assert
expected outcome
$parser = new MarkdownParser;
$html = $parser->toHtml('Hello World');
assertTrue('<p>Hello World</p>' == $html);

14. test
Arrange instantiate tested object
Act run the method
Assert check expected outcome

15. $this->toHtml('Hello World')
->shouldReturn('<p>Hello World</p>');

16. $this->toHtml('Hello World')
->shouldReturn('<p>Hello World</p>');
a test is an executable example
of a class expected behaviour

17. READY TO MOCK AROUND?

18. why?

19. class ParserSubject
{
public function notify(Event $event)
{
foreach ($this->subscribers as $subscriber) {
$subscriber->onChange($event);
}
}
}
HOW DO I KNOW NOTIFY WORKS?

20. class ParserSubjectTest extends TestCase
{
/** @test */
function it_notifies_subscribers()
{
// arrange
$parser = new ParserSubject;
// act
// I need an event!!!
$parser->notify(/* $event ??? */);
// assert
// how do I know subscriber::onChange got called?
}
}
HOW DO I KNOW NOTIFY WORKS?

21. class EndOfListListener extends EventListener
{
public function onNewLine(Event $event)
{
$html = $event->getText();
if ($this->document->getNextLine() == "") {
$html .= "</li></ul>";
}
return $html;
}
}
HOW DO I CONTROL EVENT AND DOCUMENT

22. {
focus on unit
expensive to instantiate
why? control on collaborators’ state
indirect outputs
undesirable side effects
[Meszaros 2007]

23. a mock is just 1 of
many test double patterns

24. doubles are replacement of anything
that is not the tested object

25. {
dummy
fake
doubles stub
mock
spy
[Meszaros 2007]

26. {
dummy no behaviour
fake
control indirect output
doubles stub
mock
check indirect output
spy
[Meszaros 2007]

27. a mockist TDD, London school, approach:
only the tested object is real

28. DOUBLES WITHOUT BEHAVIOUR

29. dummy
http://wicker123.deviantart.com/art/Slappy-The-Dummy-148136425

30. test
Arrange
Act
Assert

31. arrange
{
instantiate (may require collaborators)

32. class MarkdownParser
{
private $eventDispatcher;
public function __construct(EventDispatcher $dispatcher)
{
$this->eventDispatcher = $dispatcher;
}
}
USE DOUBLES TO BYPASS TYPE HINTING

33. class MarkdownParser
{
private $eventDispatcher;
public function __construct(EventDispatcher $dispatcher)
{
$this->eventDispatcher = $dispatcher;
}
}
USE DOUBLES TO BYPASS TYPE HINTING

34. class MarkdownParserTest extends TestCase
{
function setUp()
{
$dispatcher = $this->getMock('EventDispatcher');
$this->parser = new MardownParser($dispatcher);
}
}
XUNIT EXAMPLE

35. class MarkdownParser extends ObjectBehavior
{
function let($dispatcher)
{
$dispatcher->beAMockOf('EventDispatcher');
$this->beConstructedWith($dispatcher);
}
}
PHPSPEC EXAMPLE

36. http://wicker123.deviantart.com/art/Slappy-The-Dummy-148136425
“Dummy is a placeholder passed to the
SUT (tested object), but never used”
[Meszaros 2007]

37. dummy: double with no behaviour
http://wicker123.deviantart.com/art/Slappy-The-Dummy-148136425

38. DOUBLES TO CONTROL INDIRECT OUPUT

39. arrange
{
instantiate (may require collaborators)
further change state

40. class MarkdownParserTest extends TestCase
{
function setUp()
{
$dispatcher = $this->getMock('EventDispatcher');
$this->parser = new MardownParser($dispatcher);
$this->parser->setEncoding('UTF-8');
}
}
FURTHER CHANGE TO THE STATE IN ARRANGE

41. class MarkdownParserTest extends TestCase
{
function setUp()
{
$dispatcher = $this->getMock('EventDispatcher');
$this->parser = new MardownParser($dispatcher);
$this->parser->setEncoding('UTF-8');
}
}
FURTHER CHANGE TO THE STATE IN ARRANGE

42. arrange
{
instantiate (may require collaborators)
further change state
configure indirect output

43. class EndOfListListener extends EventListener
{
public function onNewLine(Event $event)
{
$html = $event->getText();
if ($this->document->getNextLine() == "") {
$html .= "</li></ul>";
}
return $html;
}
}
INDIRECT OUTPUTS

44. class EndOfListListener extends EventListener
{
public function onNewLine(Event $event)
{
$html = $event->getText();
if ($this->document->getNextLine() == "") {
$html .= "</li></ul>";
}
return $html;
}
}
INDIRECT OUTPUTS

45. fake
stub
doubles for controlling indirect output
http://www.flickr.com/photos/fcharlton/1841638596/
http://www.flickr.com/photos/64749744@N00/476724045

46. $event->getText(); // will return “Hello World”
$this->document->getNextLine(); // will return “”
STUBBING: CONTROLLING DOUBLES INDIRECT OUTPUTS

47. function let($event, $document)
{
$event->beAMockOf("Event");
$document->beAMockOf("Document");
$this->beConstructedWith($document);
}
IN PHPSPEC

48. function let($event, $document)
{
$event->beAMockOf("Event");
$document->beAMockOf("Document");
$this->beConstructedWith($document);
}
function it_ends_list_when_next_is_empty($event, $document)
{
$event->getText()->willReturn("Some text");
$document->getNextLine()->willReturn("");
}
IN PHPSPEC

49. function let($event, $document)
{
$event->beAMockOf("Event");
$document->beAMockOf("Document");
$this->beConstructedWith($document);
}
function it_ends_list_when_next_is_empty($event, $document)
{
$event->getText()->willReturn("Some text");
$document->getNextLine()->willReturn("");
$this->onNewLine($event)
->shouldReturn("Some text</li></ul>");
}
IN PHPSPEC

50. class EndOfListListener extends EventListener
{
public function onNewLine(Event $event)
{
$html = $event->getText();
if ($this->document->getNextLine() == "") {
$html .= "</li></ul>";
}
return $html;
}
}
THE CODE AGAIN

51. function let($event, $document)
{
$event->beAMockOf("Event");
$document->beAMockOf("Document");
$this->beConstructedWith($document);
}
function it_ends_list_when_next_is_empty($event, $document)
{
$event->getText()->willReturn("Some text");
$document->getNextLine()->willReturn("");
$this->onNewLine($event)
->shouldReturn("Some text</li></ul>");
}
THE SPEC AGAIN

52. double behaviour
loose demand returns null to any method call
fake returns null to defined set methods
stub returns value defined or raise error

53. DOUBLES TO SPEC MESSAGE EXCHANGE

54. we said before
a test is an executable example
of a class expected behaviour

55. what is behaviour?

56. B = I + O
behaviour = input + output

57. what can happen in a method?

58. {
return a value
modify state
methods print something
throw an exception
delegate

59. {
return a value
not the final
modify state
behaviour
methods print something
throw an exception
delegate

60. {
methods
return a value we should probably
print something delegate that too
throw an exception
delegate

61. {
methods
return a value
throw an exception
delegate

62. method strategy
returns a value
throws an exception
delegates

63. method strategy
returns a value assertions/
throws an exception expectations
delegates mocks & spies

64. Viewpoints Research Institute Source - Bonnie Macbird URL -http://www.vpri.org
“The key in making great and growable systems is much more to
design how its modules communicate
rather than what their internal properties
and behaviours should be.”
Messaging

65. messaging

66. yeah, but what does it mean?

67. $this->person->getCar()->getEngine()->ignite();

68. Inappropriate Intimacy

69. $this->person->startCar();

70. tell, don’t ask!
[Sharp 1997]

71. exposing lower level implementation
makes the code rigid

72. $this->person->getCar()->getEngine()->ignite();

73. focus on messaging
makes the code flexible

74. $this->person->startCar();

75. mock
spy
doubles for messaging
http://www.flickr.com/photos/scribe215/3234974208/
http://www.flickr.com/photos/21560098@N06/5772919201/

76. class ParserSubject
{
public function notify(Event $event)
{
foreach ($this->subscribers as $subscriber) {
$subscriber->onChange($event);
}
}
}
HOW DO I KNOW NOTIFY WORKS?

77. class ParserSubject
{
public function notify(Event $event)
{
foreach ($this->subscribers as $subscriber) {
$subscriber->onChange($event);
}
}
}
HOW DO I KNOW NOTIFY WORKS?

78. use mocks to describe how your
method will impact collaborators

79. use PHPUnit_Framework_TestCase as TestCase;
class ParserSubjectTest extends TestCase
{
/** @test */ function it_notifies_subscribers()
{
$event = $this->getMock("Event");
$subscriber = $this->getMock("Subscriber");
$subscriber->expects($this->once())
->method("onChange")
->with($event);
$parser = new ParserSubject();
$parser->attach($subscriber);
$parser->notify($event);
}
}
USING PHPUNIT NATIVE MOCK CONSTRUCT

80. public function testUpdateWithEqualTypes()
{
$installer = $this->createInstallerMock();
$manager = new InstallationManager('vendor');
$manager->addInstaller($installer);
$initial = $this->createPackageMock();
$target = $this->createPackageMock();
$operation = new UpdateOperation($initial, $target, 'test');
$initial
->expects($this->once())
->method('getType')
->will($this->returnValue('library'));
$target
->expects($this->once())
->method('getType')
->will($this->returnValue('library'));
$installer
->expects($this->once())
->method('supports')
->with('library')
->will($this->returnValue(true));
$installer
->expects($this->once())
->method('update')
->with($this->repository, $initial, $target);
EXCESSIVE SETUP

81. github.com/padraicb/mockery

82. use PHPUnit_Framework_TestCase as TestCase;
class ParserSubjectTest extends TestCase
{
/** @test */ function it_notifies_subscribers()
{
$event = Mockery::mock("Event");
$subscriber = Mockery::mock("Subscriber");
$subscriber->shouldReceive("onChange")
->with($event);
$parser = new ParserSubject();
$parser->attach($subscriber);
$parser->notify($event);
}
}
USING MOCKERY

83. class ParserSubject extends PHPSpec2ObjectBehavior
{
/**
* @param Event $event
* @param Subscriber $subscriber
*/
function it_notifies_subscribers($event, $subscriber)
{
$subscriber->onChange($event)->shouldBeCalled();
$this->attach($subscriber);
$this->notify($event);
}
}
SAME EXAMPLE IN PHPSPEC

84. use spies to describe indirect output
expectations, retrospectively

85. github.com/dancras/doubles

86. use PHPSpec2ObjectBehavior;
class ParserSubject extends ObjectBehavior
{
function it_notifies_subscribers()
{
$event = Doubles::fromClass('Event');
$subscriber = Doubles::fromClass('Subscriber');
$this->attach($subscriber);
$this->notify($event);
$subscriber->spy('onChange')->callCount()->shoudBe(1);
}
}
SPY EXAMPLE – WITH “DOUBLES” FRAMEWORK

88. use PHPSpec2ObjectBehavior;
class ParserSubject extends ObjectBehavior
{
/**
* @param Event $event
* @param Subscriber $subscriber
*/
function it_notifies_subscribers($event, $subscriber)
{
$this->attach($subscriber);
$this->notify($event);
$subscriber->onChange($event)
->shouldHaveBeenCalled();
}
}
SPY EXAMPLE – AVAILABLE WITH PROPHECY INTEGRATION

89. use ProphecyProphet;
class TestCase extends SomeUnitTestingFrameworkTestCase
{
function createDoubler($name)
{
$this->prophet = new ProphecyProphet;
return $this->prophet->prophesize($name);
}
function createDummy($name)
{
return $this->createDoubler($name)->reveal();
}
}
INTEGRATING PROPHECY

90. {
dummy no behaviour
fake
control indirect output
doubles stub
mock
messaging
spy
[Meszaros 2007]

91. Marcello Duarte
I work here
I contribute here
I tweet here @_md

92. Thank you !

93. Questions or Comments?
want to improve on testing? bit.ly/inviqa-bdd-training