Test Driven Design really helps us learn about the design of our code and how to improve on it. It is also true that the more we know about design, the more our code can actually benefit from TDD. This talk will cover just enough to give you the design inspiration you need to appreciate TDD. We will see responsibility driven design, "Tell don't ask", the law of Demeter, Dependency Inversion and other very key design principles and how they change the way we look into coding and testing

1. by@_md
Barely
Design
*
Enough

2. Iworkhere
Icontributehere
Itweethere @_md
MarcelloDuarte

3. bigdesignmotivators
principlesbehindsimplicity
responsibility-drivenprocess{

5. IT’SHARDTOCHANGELATER.

6. WENEEDTOTHINKABOUTTHINGSBEFOREDEVELOPING.

7. WENEEDTOMAKESUREWEDON’TMISSANYTHING.

8. THISISJUSTTHEWAYWEDOIT.

10. proceduralprogrammersarecomfortable
withdata-drivendesign

11. class SomethingPeopleCallEntity
{
public function getABitOfThis()
{
return $this->aBitOfThis;
}
public function getABitOfThat()
{
return $this->aBitOfThat;
}
public function getABitOfTheOtherThing()
{
return $this->aBitOfTheOtherThing;
}
public function getSomeOfThis()
{
return $this->someOfThis;
}
public function getSomeOfThat()
{
return $this->someOfThat;
}
public function getSomeOfTheOtherThing()
{
return $this->someOfTheOtherThing;
}

13. demeter
For all classes C,
and for all methods M attached to C,
all objects to which M sends a message
must be instances of classes
associated with the following classes:
1.The argument classes of M (including C.)
2.The instance variable classes of C.

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

15. leadsustonamingafterstructure
fragility
viscosity
disregardtoencapsulation{
data-driven

16. onlytalktoimmediatefriends
demeter

17. minimisetheinteractionbetweenobjects
tell don’t ask

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

19. putthebehaviourwherethedatais
tell don’t ask

20. simplicity

21. “Getitdoneintenminutesandmoveon.Savethebig
sortimplementationforwhenthegoldownersdecide
thesystemistooslow.
Encapsulationwillsaveyou.”
Ron Jeffries
simplicity

23. abstraction |əәbˈstrakʃ(əә)n|
noun [ mass noun ]
1 the quality of dealing with ideas rather than events: topics
will vary in degrees of abstraction.
• [ count noun ] something which exists only as an idea: the
question can no longer be treated as an academic abstraction.
2 freedom from full representation
in art:geometric abstraction has been a mainstay in her work.

24. class TestRunner
{
public function __construct(ProgressFormatter $formatter)
{
$this->progressFormatter = $formatter;
}
public function run(Test $test)
{
try {
$test->run();
$this->progressFormatter->markPass();
} catch (Exception $e) {
$this->progressFormatter->markFail($e);
}
}
}

25. “Customersknow!
Conferenceroomwithevillittleminds:muahaha!”
Uncle Bob
change

26. WENEEDANYANCATFORMATTERNOW!

27. class NyanCatFormatter extends ProgressFormatter
{
}

28. http://mmw-blog.blogspot.co.uk/2010/07/happy-women-joyful-freedom-happiness.html

30. class TestRunner
{
public function __construct(Formatter $formatter)
{
$this->formatter = $formatter;
}
public function run(Test $test)
{
try {
$test->run();
$this->formatter->markPass();
} catch (Exception $e) {
$this->formatter->markFail($e);
}
}
}

31. class NyanCat implements Formatter
{
}

32. abstractrolesthatcanchange

33. «interface»
Formatter
+ markPass()
+ markFail()
interface=role+responsibilities

34. messaging

35. «interface»
Formatter
+ markPass()
+ markFail()
Test Runner
+ run(:Test)
Progress NyanCat
…

36. whendowedecidetoaddanabstraction

37. "Makethecommitmentatthelast
responsiblemoment"
Preston Smith
decide later

38. designsoyoucancommitlater

39. fabric

40. objects
values
{
concepts

41. identity
state
behaviour
{objects

42. entitieshaveidentitiesandstate
whynotusetheminyouOOdesign?

43. process

44. “ThefullbenefitofOOcanonlyberealizedif
encapsulationismaximisedduringthedesignprocess.
RDDspecifiesobjectbehaviourbeforeobjectstructure
andotherimplementationconsiderationsaremade.”
Rebecca Wirfs-Brock
responsibilities

45. “Wehavefoundthatthemosteffectivewayofteaching
theidiomaticwayofthinkingwithobjectsistoimmerse
thelearnerinthe"object-ness"ofthematerial.”
Ward Cunningham
CRC

46. identifyscenarios
listresponsibilities
identifyroles,values
dreamtheboundaries
{ CRC

47. CRC

48. Course
Students
LessonsEnrol students
Display outline/info
Keep track of
vacancies
CRC

49. “Knowinadvancewhereyouaregoingtoputcertain
behaviours. […]Inshort,beforeyouwriteyourfirst
test,youhavetodreamupthe[boundaries]thatyou
wishyouhad.”
Uncle Bob
boundaries

50. Dependency
Inversion
Principle
[Martin 02]
Behaviour
Collaborator
Collaborator
Role
Role

51. class CompetencyFinder
{
private $learner;
private $finder;
public function __construct(Learner $learner, CompetencyDictionaryFinder $finder)
{
$this->learner = $learner;
$this->finder = $finder;
}
public function findDictionary()
{
return $this->finder->findByLearnerRole($this->learner->getLearnerRole());
}
}

52. interface CompetencyDictionaryFinder
{
/**
* Gets the dictionary for a particular role
*
* @param LearnerRole $role
* @return InviqaLearningCompetencyDictionary
*/
public function findByLearnerRole(LearnerRole $role);
}

53. /**
* @Route(service="controllers.skills")
*/
class SkillsController
{
private $competencyFinder;
private $raterFinder;
public function __construct(CompetencyFinder $competencyFinder)
{
$this->competencyFinder = $competencyFinder;
}
/**
* @Route("/skills", name="skills")
* @Template()
* Show the skill for the learners role
*/
public function indexAction()
{
return ['competencies' => $this->competencyFinder->findDictionary()];
}
}

54. class Skill
{
private $skillChanges;
public static function rate($skill, Learner $learner, Rating $rating)
{
$skillChange = new SkillChangeEvent($skill, $learner, $rating);
$skill = new Skill();
$skill->skillChanges[] = $skillChange;
}
public function getSkillChanges()
{
return $skill->skillChanges;
}
}

55. tdd

56. usescenariosandexamples
tobuildyourdomain

57. considerinvertingdependencies
aroundtheboundaries

58. firstlearndesign
thentest-drivendesign

59. usetherighttoolsfortherightjob

60. concluding

61. bigdesignmotivators
principlesbehindsimplicity
responsibility-drivenprocess
learndesignthenTDD{

62. Iworkhere
Icontributehere
Itweethere @_md
MarcelloDuarte

63. Thankyou
joind.in/13373

64. Credits
http://earthymoon.deviantart.com/art/Elephant-png-122633500
http://mmw-blog.blogspot.co.uk/2010/07/happy-women-joyful-
freedom-happiness.html