The slides of my Fake It Outside-In TDD session at Softwerkskammer Meetup Munich. Some improved screencasts you can find here: https://www.youtube.com/playlist?list=PL_ueet93U84VIy8O7U4dUV0GyGvuzFAt8

1. FAKE IT OUTSIDE-IN TDD
David Völkel
9th May @ Softwerkskammer Meetup Munich

2. @DAVIDVOELKEL
@codecentric
@softwerkskammer
#TDD
#software_design

3. INFLUENCES
2003 Kent Beck’s "Fake It" Pattern
2009 #GOOS’s "Outside-In" Design
2013 Emily Bache
"Outside-In development with Double Loop TDD"
2014 Justin Searls "The Failures of 'Intro to TDD'"
COMBINATION
2015 Dimitry Polivaev Outside-In with faked Data
2016 SoCraTes DE Outside-In Fake It Session
2017 Refinement

4. INFLUENCES
2003 Kent Beck’s "Fake It" Pattern
2009 #GOOS’s "Outside-In" Design
2013 Emily Bache
"Outside-In development with Double Loop TDD"
2014 Justin Searls "The Failures of 'Intro to TDD'"
COMBINATION
2015 Dimitry Polivaev Outside-In with faked Data
2016 SoCraTes DE Outside-In Fake It Session
2017 Refinement

5. INFLUENCES
2003 Kent Beck’s "Fake It" Pattern
2009 #GOOS’s "Outside-In" Design
2013 Emily Bache
"Outside-In development with Double Loop TDD"
2014 Justin Searls "The Failures of 'Intro to TDD'"
COMBINATION
2016 SoCraTes DE Outside-In Fake It Session
2017 Refinement

6. INFLUENCES
2003 Kent Beck’s "Fake It" Pattern
2009 #GOOS’s "Outside-In" Design
2013 Emily Bache
"Outside-In development with Double Loop TDD"
2014 Justin Searls "The Failures of 'Intro to TDD'"
COMBINATION
2016 SoCraTes DE Outside-In Fake It Session
2017 Refinement

7. INFLUENCES
2003 Kent Beck’s "Fake It" Pattern
2009 #GOOS’s "Outside-In" Design
2013 Emily Bache
"Outside-In development with Double Loop TDD"
COMBINATION
2016 SoCraTes DE Outside-In Fake It Session
2017 Refinement

8. INFLUENCES
2003 Kent Beck’s "Fake It" Pattern
2009 #GOOS’s "Outside-In" Design
2013 Emily Bache
"Outside-In development with Double Loop TDD"
2014 Justin Searls "The Failures of 'Intro to TDD'"
COMBINATION
2016 SoCraTes DE Outside-In Fake It Session
2017 Refinement

9. AGENDA
Theory
Building Blocks
Fake It Outside-In
Practice
Kata
Reflect
Retro
Trade-Offs
Discussion

10. BUILDING BLOCKS

11. INTEGRATION OPERATION
SEGREGATION PRINCIPLE
*"Integration Operation Segregation Principle", Ralf Westphal
"Die kniffligen Fälle beim Testen - Sichtbarkeit", Stefan Lieser
*

12. INTEGRATION OPERATION
SEGREGATION PRINCIPLE
public void sendDiscountMailingTo(String email) {
Customer customer = customerDB.findCustomerBy(email);
Account account = customer.account();
String discount = account == FREE ? "no" :
account == BASE ? "a 10%" :
account == PREMIUM ? "a 25%" :
"-ERROR-";
String content = "Hello " + customer.getName() + ",nn" +
"This week you get " + discount + " discount " +
"on all our products.nn" +
"Best Regards,n" + "ACME Customer Service";
mailService.sendMail(email, content);
}

13. OPERATION
public void sendDiscountMailingTo(String email) {
Customer customer = customerDB.findCustomerBy(email);
Account account = customer.account();
String discount = account == FREE ? "no" :
account == BASE ? "a 10%" :
account == PREMIUM ? "a 25%" :
"-ERROR-";
String content = "Hello " + customer.getName() + ",nn" +
"This week you get " + discount + " discount " +
"on all our products.nn" +
"Best Regards,n" + "ACME Customer Service";
mailService.sendMail(email, content);
}
INTEGRATION OPERATION
SEGREGATION PRINCIPLE

14. OPERATION
public void sendDiscountMailingTo(String email) {
Customer customer = customerDB.findCustomerBy(email);
Account account = customer.account();
String discount = account == FREE ? "no" :
account == BASE ? "a 10%" :
account == PREMIUM ? "a 25%" :
"-ERROR-";
String content = "Hello " + customer.getName() + ",nn" +
"This week you get " + discount + " discount " +
"on all our products.nn" +
"Best Regards,n" + "ACME Customer Service";
mailService.sendMail(email, content);
}
INTEGRATION OPERATION
SEGREGATION PRINCIPLE
INTEGRATION
INTEGRATION

15. OPERATION
public void sendDiscountMailingTo(String email) {
Customer customer = customerDB.findCustomerBy(email);
Account account = customer.account();
String discount = account == FREE ? "no" :
account == BASE ? "a 10%" :
account == PREMIUM ? "a 25%" :
"-ERROR-";
String content = "Hello " + customer.getName() + ",nn" +
"This week you get " + discount + " discount " +
"on all our products.nn" +
"Best Regards,n" + "ACME Customer Service";
mailService.sendMail(email, content);
}
INTEGRATION OPERATION
SEGREGATION PRINCIPLE
INTEGRATION
INTEGRATION

16. OPERATION
INTEGRATION
public void sendDiscountMailingTo(String email) {
Customer customer = customerDB.findCustomerBy(email);
String content = renderMessage(customer, customer.account());
mailService.sendMail(email, content);
}
private String renderMessage(Customer customer, Account account) {
String discount = account == FREE ? "no" :
account == BASE ? "a 10%" :
account == PREMIUM ? "a 25%" :
"-ERROR-";
return "Hello " + customer.getName() + ",nn" +
"This week you get " + discount + " discount " +
"on all our products.nn" +
"Best Regards,n" + "ACME Customer Service";
}
INTEGRATION OPERATION
SEGREGATION PRINCIPLE

17. public void sendDiscountMailingTo(String email) {
Customer customer = customerDB.findCustomerBy(email);
String content = renderMessage(customer, customer.account());
mailService.sendMail(email, content);
}
private String renderMessage(Customer customer, Account account) {
String discount = account == FREE ? "no" :
account == BASE ? "a 10%" :
account == PREMIUM ? "a 25%" :
"-ERROR-";
return "Hello " + customer.getName() + ",nn" +
"This week you get " + discount + " discount " +
"on all our products.nn" +
"Best Regards,n" + "ACME Customer Service";
}
TESTS?

18. OPERATION
public void sendDiscountMailingTo(String email) {
Customer customer = customerDB.findCustomerBy(email);
String content = renderMessage(customer, customer.account());
mailService.sendMail(email, content);
}
private String renderMessage(Customer customer, Account account) {
String discount = account == FREE ? "no" :
account == BASE ? "a 10%" :
account == PREMIUM ? "a 25%" :
"-ERROR-";
return "Hello " + customer.getName() + ",nn" +
"This week you get " + discount + " discount " +
"on all our products.nn" +
"Best Regards,n" + "ACME Customer Service";
}
TESTS?
N UNITTESTS

19. OPERATION
INTEGRATION
public void sendDiscountMailingTo(String email) {
Customer customer = customerDB.findCustomerBy(email);
String content = renderMessage(customer, customer.account());
mailService.sendMail(email, content);
}
private String renderMessage(Customer customer, Account account) {
String discount = account == FREE ? "no" :
account == BASE ? "a 10%" :
account == PREMIUM ? "a 25%" :
"-ERROR-";
return "Hello " + customer.getName() + ",nn" +
"This week you get " + discount + " discount " +
"on all our products.nn" +
"Best Regards,n" + "ACME Customer Service";
}
TESTS?1 INTEGRATION TEST
N UNITTESTS

20. GREEN BAR PATTERNS*
Obvious Implementation
Fake it (until you make it)
Triangulation
* Kent Beck in "TDD by Example"

21. GREEN BAR PATTERNS
DEMO

22. GREEN BAR PATTERNS
Obvious Implementation
Fake it
Triangulation
Trade-Off
Complexity

23. SWEET SPOT
Logic
GREEN BAR PATTERNS
Obvious Implementation
Fake it
Triangulation

24. SWEET SPOT
Structure
Logic
GREEN BAR PATTERNS
Obvious Implementation
Fake it
Triangulation

25. SWEET SPOT
Trivial
Structure
Logic
GREEN BAR PATTERNS
Obvious Implementation
Fake it
Triangulation

26. INTEGRATION
OPERATION
Fake it
Triangulation
GREEN BAR PATTERNS
Structure
Logic
IOSP

27. INTER-OBJECT DESIGN
EMERGENT
INSIDE-OUT
OUTSIDE-IN & MOCKS
OUTSIDE-IN & FAKE IT

28. Acceptance Test
EMERGENT

29. Acceptance Test
EMERGENT

30. Acceptance Test
EMERGENT

31. Acceptance Test Design through
Refactoring
EMERGENT

32. Acceptance Test
EMERGENT

33. Acceptance Test
UI
Persistence
EMERGENT

34. UI df
Persistence nc.
Unit Test
INSIDE-OUT

35. nc.
Unit Test
INSIDE-OUT

36. Unit Test
INSIDE-OUT

37. Acceptance Test
INSIDE-OUT

38. Acceptance Test
UI
Persistence
OUTSIDE-IN

39. Unit test
Mock
OUTSIDE-IN & MOCKS

40. Unit Test
OUTSIDE-IN & MOCKS

41. Acceptance Test
UI
Persistence
OUTSIDE-IN & MOCKS

42. Comprehensive
Acceptance Test
OUTSIDE-IN & FAKE IT

43. Comprehensive
Acceptance Test
Faked Result
OUTSIDE-IN & FAKE IT

44. Acceptance Test
Fake
Fake
OUTSIDE-IN & FAKE IT

45. Acceptance Test Drive Structure
through Refactoring
OUTSIDE-IN & FAKE IT

46. OUTSIDE-IN & FAKE IT
Acceptance Test
Unit Test
Fill logic with
triangulation

47. OUTSIDE-IN & FAKE IT
Acceptance Test Unit Test

48. INTEGRATION
OUTSIDE-IN & FAKE IT
OPERATION
Fake It
Triangulation
Start with
• comprehensive
Acceptance Test
• faked result
Drive structure by refactoring
Drive logic by unit tests

49. INTEGRATION
OUTSIDE-IN & FAKE IT
OPERATION
Fake It
Triangulation
Start with
• comprehensive
Acceptance Test
• faked result
Drive structure by refactoring
Drive logic by unit tests

50. FAKE IT OUTSIDE-IN
DEMO

51. PREPARATORY REFACTORINGS*
*"An example of preparatory refactoring", Martin Fowler

52. "GREEN" PHASE
Implementation Run Test
"Green Phase"

53. LIMIT YOUR TIME IN RED
"Green Phase"
Implementation Run Test
Implementation Run TestPreparatory Refactoring

54. PREPARATORY REFACTORINGS
DEMO

55. FAKE-IT VARIANT
CALCULATE BACKWARDS
DEMO

56. PRACTICE

57. CODING SESSION
KATA
Diamond Kata

58. CODING SESSION
KATA
Diamond Kata
CONSTRAINTS
Start with comprehensive Acceptance Test & faked result
Drive structure by refactoring
Drive conditionals by unit tests & triangulation

59. RETROSPECTIVE

60. RETROSPECTIVE
Observations?

61. RETROSPECTIVE
Observations?
Strengths?

62. RETROSPECTIVE
Observations?
Strengths?
Weaknesses?

63. VSTRADE-OFFS
TDD APPROACHES

64. Design uncertainty Overhead if design clear
Only Integration Tests
EMERGENT
+ -

65. INSIDE-OUT
3rd Party Integration YAGNI Design Potential
+ -

66. OUTSIDE-IN & MOCKS
No YAGNI Design
Decoupled Classes
Interaction Complexity
Refactorability
+ -

67. OUTSIDE-IN & FAKE IT
No YAGNI &
No Mocks
Higher Coupling
Fake data easy to forget
Omitting cases is tempting
+ -

68. SWEET SPOTS
Triangulation Fake It
#Branches N 1

69. SWEET SPOTS
Triangulation Fake It
#Branches N 1
Structure Cumbersome Data guides well

70. SWEET SPOTS
Triangulation Fake It
#Branches N 1
Structure Cumbersome Data guides well
Baby Steps
Through Preparatory
Refactorings
Easy

71. DISCUSSION

72. LICENSE
Creative Commons Attribution-ShareAlike 3.0

73. IMAGES
Most are Public Domain except theses
Creative Commons with attributions:
"Unstruttalbrücke" by Störfix
From State Library of Queensland