The document describes a workshop on the Fake It Outside-In Test Driven Development (TDD) technique. It discusses influences on the technique from 2003-2017 and combinations of patterns. The workshop goals are to understand TDD patterns and tradeoffs of Fake It vs triangulation and Fake It vs Outside-In mocking. The agenda includes building blocks, theory, screencasts, exercises, a coding kata in pairs, and reflection.

1. FAKE IT OUTSIDE-IN TDD
WORKSHOP
David Völkel
20th June 2017 @ Clean Code Days
https://github.com/davidvoelkel/fake-it-outside-in-tdd-workshop-clean-code-days

2. @DAVIDVOELKEL
@codecentric
@softwerkskammer
#TDD

3. YOU?
Language/IDE?
TDD background?
Expectations for today?

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
2015 Dimitry Polivaev Outside-In with faked Data
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
COMBINATION
FAKE IT OUTSIDE-IN TDD

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"
2014 Justin Searls "The Failures of 'Intro to TDD'"
COMBINATION
2016 SoCraTes DE Outside-In Fake It Session

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 / Work in Progress

9. 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 / Work in Progress

10. 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 / Work in Progress

11. 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'"
2017 Llewelyn Falco "Extreme: Fake it Till you Make It"
COMBINATION
2016 SoCraTes DE Outside-In Fake It Session
2017 Refinement / Work in Progress

12. TODAY’S GOALS
Unterstand TDD patterns & trade-offs
Fake It vs. Triangulation
Fake It vs. Outside-In Mocking
Get to a sequence of very small steps

13. AGENDA
Building Blocks
Theory/Slides
Screencasts
Small Exercises (Mob)
Fake It Outside-In
Big Kata (Pairs)
Reflect
Retro
Assessment
Focus
Big Picture

14. BUILDING BLOCKS

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

16. 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);
}

17. 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

18. INTEGRATION
INTEGRATION
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

19. INTEGRATION
INTEGRATION
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

20. 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

21. 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?

22. 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

23. INTEGRATION
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?1 INTEGRATION TEST
N UNITTESTS

24. CODING SESSION
KATA
Refactoring of
credit-application/…/
CreditApplicationController.performScoring()
Tasks / Constraints
Enforce IOSP: Segregate Operation from Integration
Check (unit) testability

25. Benefits?
Limits?
REFLECT IOSP

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

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

28. GREEN BAR PATTERNS
DEMO

29. GREEN BAR PATTERNS
Obvious Implementation
Fake it
Triangulation Fake Result
Refactor
Big Step
Fake Result
2nd Test

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

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

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

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

34. DECOMPOSE FAKE DATA
TO BUILD STRUCTURE

35. CODING SESSION
KATA
assertThat(format(LocalDate.of(2017, 6, 21)))
.isEqualTo("2017-06-21");
Tasks / Constraints
Obvious Implementation
Fake it / Decompose as long as possible
Then triangulate the remaining logic
Triangulate with fake data

36. Obvious Impl.
Fake It
Triangulation
Properties?
Strengths?
Weaknesses?
GREEN BAR PATTERNS

37. DATA GUIDES STRUCTURE
Triangulation Fake It
Structure Cumbersome Data guides well

38. # BRANCHES
Triangulation Fake It
# N 1
More confidence
More effort

39. # BRANCHES
Triangulation Fake It
# N 1
Fake data easy to forget
Omitting cases is
tempting

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

41. "GREEN" PHASE TRIANGULATION
Implementation Run Test
"Green Phase"

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

43. PREPARATORY REFACTORINGS
DEMO

44. FAKE-IT VARIANT
CALCULATE BACKWARDS
DEMO

45. CODING SESSION
KATAS
assertThat(sum(„1,2,3")).isEqualTo(6);
assertThat(toCharacters(asList(0, 1, 2)))
.isEqualTo("a,b,c");
Tasks / Constraints
Working Backwards
Decompose
Preparatory Refactoring

46. Working Backwards
Preparatory Refactorings
Observations?
Why / Benefits?
REFLECT

47. TIME IN GREEN
Triangulation
Prep Refactoring
Triangulation
Fake It

48. Acceptance Test
UI
Persistence
OUTSIDE-IN

49. Unit test
Mock
OUTSIDE-IN & MOCKS

50. Unit Test
OUTSIDE-IN & MOCKS

51. Acceptance Test
UI
Persistence
OUTSIDE-IN & MOCKS

52. Comprehensive
Acceptance Test
OUTSIDE-IN & FAKE IT

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

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

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

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

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

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

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

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

61. DIAMOND KATA

62. FAKE IT OUTSIDE-IN
DEMO

63. PAIRING SESSION
KATA
Continue Diamond Kata
https://github.com/davidvoelkel/diamond-kata
CONSTRAINTS
Drive structure by refactoring
Drive conditionals by triangulation

64. What did you observe?
What worked?
What was hard?
REFLECT KATA

65. Fake It
vs Outside-in & Mocks
vs Triangulation
REFLECT TRADE-OFFS

66. TRADE-OFFS
FAKE IT VS
OUTSIDE-IN & MOCKS
TRIANGULATION

67. CONDITIONAL INTERACTIONS
Mocking when IOSP not possible
public String signup(String username) throws Exception {
if(userDB.findUserBy(username) == null) {
userDB.createUser(new User(username));
return "Welcome " + username;
} else {
return "Username ' " + username + "' "
+ "already taken, please choose another";
}
}

68. COUPLING OUTSIDE-IN
Mocking Fake It
Decoupling Refactorability

69. DATA GUIDES STRUCTURE
Triangulation Fake It
Structure Cumbersome Data guides well

70. # BRANCHES
Triangulation Fake It
# N 1
More confidence
More effort

71. # BRANCHES
Triangulation Fake It
# N 1
Fake data easy to forget
Omitting cases is
tempting

72. What surprised you?
What did you learn?
What will you take into your project?
CONTENT REFLECTION

73. What did you (not) like?
What could be improved?
SESSION REFLECTION

74. THANK YOU!

75. REFERENCES
2003 Kent Beck’s "TDD by Example“: “Fake It" Pattern
2009 Steve Freeman, Nat Pryce:
„Growing Object Oriented Software Guide by Tests“:
"Outside-In" Design
2013 Emily Bache
"Outside-In development with Double Loop TDD"
2014 Justin Searls "The Failures of 'Intro to TDD'"
2017 Llewelyn Falco "Extreme: Fake it Till you Make It"

76. EXERCISE CODE SAMPLES
https://github.com/davidvoelkel/fake-it-outside-in-tdd-workshop-clean-code-days
SCREENCASTS
Playlist on Youtube

77. LICENSE
Creative Commons Attribution-ShareAlike 3.0

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