There are two different schools of TDD: the "London School of TDD" ("Mockists") with proponents like Steve Freeman, Nat Pryce, J.B. Rainsberger leverage a top-down approach and heavy use of interfaces to craft roles of neighbour objects. They drive their design "outside-in" starting with end-to-end acceptance tests and focus on the interaction between objects. Testing them in isolation is achieved by heavy use of mocking. On the contrary the "Chicago School of TDD" ("Classicists" like Kent Beck, Uncle Bob, ...) try to avoid mocks if possible. They prefere "state based testing" and focus on assertions on the return values. References: Blogpost "Mocks aren't Stubs", Martin Fowler: http://martinfowler.com/articles/mocksArentStubs.html Paper "Mock Roles not objects", Freeman et al.: http://jmock.org/oopsla2004.pdf Book "Growing Object Oriented Software guided by tests", Steve Freeman & Nat Pryce: http://www.growing-object-oriented-software.com/

1. Mockist vs. Classicist TDD
Softwerkskammer Regionalgruppentreffen München
30.10.2014
David Völkel

2. Agenda
●Theory
●Pizza
●Kata

3. Classicists vs. Mockists
●Who knows?

4. Classicists vs. Mockists
●Who knows?
●Who leverages what?

5. Mockists?

6. Classicists?

7. How i stumbled upon…
●#GOOS
●#IsTDDDead
●Outside-In 
●Mocking 
●=> How work Classicist?

8. Classicists
●„old school“: Kent Beck, Uncle Bob, …
●state verification
●bottom-up/inside-out
●Avoid mocks when possible

9. Mockists
●„London School“: Steve Freeman, Nat Pryce
●XP 2000 „Endo-Testing: Unit Testing with Mock Objects “
●OOPSLA 2004 „Mock Roles, not Objects“
●Book „Growing Object Oriented Software“ #GOOS 2009

10. Mockists
●ATDD
●Outside-In Design
●Hexagonal / Ports&Adapters Architecture
●also for classicists
●Mocking to isolate layers
●Interaction based testing
●„Back-door“

11. Architecture
●Mockist OO-style
●Message Passing/Event-Architecture
●Topology / Message flow
●„Tell don‘t ask“
●Classicist FP-style
●mutable objects encapsulating state
●pure functions & immutable value objects
●details: algorithms, logic, conditionals

12. Layer
UI
Domain
Data Access
DB

13. Domain
Hexagonal / Ports & Adapters
UI
Domain Service
Repository DB Adapter
DB
Repository Interface

14. Hexagonal / Ports & Adapters
Domain Service
Repository DB Mock
DB
Repository Interface
Unit Test

15. ATDD
From Growing Object-Oriented Software by Nat Pryce and Steve Freeman

16. Outside-In Design
UI
Domain Service
Repository DB Adapter
DB
End2End Test

17. Outside-In Design
UI
Domain Service
Repository DB Adapter
DB
Domain Service Interface
Unit Test
End2End Test

18. Outside-In Design
UI
Domain Service
Repository DB Adapter
DB
Repository Interface
Domain Service Interface
Unit Test
Unit Test
End2End Test

19. Outside-In Design
UI
Domain Service
Repository DB Adapter
DB
Repository Interface
Domain Service Interface
Unit Test
Unit Test
Integration
Test
End2End Test

20. Classicists Design
●Bottom-up
●emergent
●„TDD as if you meant it“ (YAGNI?)
●Middle ground?
●Acceptance tests => Domain

21. Classicist IO
out = pureFunction(in);
object.changeStateBasedOn(in);
out = object.getState();
●Functional
●State-based

22. Mockist IO: CQS
public Object myQuery() {
return neighbour.query();
}
when(neighbour.query()).thenReturn(in);
●Queries: Stubbing indirect input

23. Mockist IO: CQS
public Object myQuery() {
return neighbour.query();
}
when(neighbour.query()).thenReturn(in);
private void myCommand() {
neighbour.command(out);
}
verify(neighbour).command(out);
●Queries: Stubbing indirect input
●Commands: Spies check indirect output

24. Let‘s code!
●Content: Kata „Game of Life“
●Phase 1: Outside-In Mockist style
●Mockless Classicist design
●Phase 2: refactor to mockless Classicist design
●Mode: Mob Programming
●1 Driver
●N Navigators
●Variant: David = PO & facilitator

25. Outside-In Mockist style

26. Classicist Isolation
●No isolation = „front door“
●Leaf
●Integrated test
●By design
●Context independence: parameterize methods/constructors, values/value objects, intermediary results
●„Functional Core, Imperative Shell“

27. String renderMail(String mail) {
String name = userRepo.nameFor(mail);
return renderMailAndName(mail, name);
}
@Test public void renderMail() {
when(userRepo.nameFor("customer@gmail.com"))
.thenReturn("Joe Customer");
assertEquals("customer@gmail.com <Joe Customer>",
mailService.renderMail("customer@gmail.com"));
}
Isolation via mocks

28. String renderMail(String mail) {
String name = userRepo.nameFor(mail);
return renderMailAndName(mail, name);
}
@Test public void renderMail() {
when(userRepo.nameFor("customer@gmail.com"))
.thenReturn("Joe Customer");
assertEquals("customer@gmail.com <Joe Customer>",
mailService.renderMail("customer@gmail.com"));
}
@Test public void renderMail() {
assertEquals("customer@gmail.com <Joe Customer>",
mailService.renderMailAndName("customer@gmail.com", "Joe Customer"));
}
Mockless isolation

29. Refactor mocks away

30. Retrospective

31. Bilder
von RaminusFalcon
http://commons.wikimedia.org/wiki/File:Split- scissors.svg?uselang=de

32. Lizenz
Creative Commons Attribution-ShareAlike 3.0
https://creativecommons.org/licenses/by-sa/3.0/de/

33. TDD as if you meant it
1.Write exactly one failing test
2.Make the test pass by writing implementation code in the test method
3.When duplication is spotted extract the implementation from tests to:
1. a new method in the test class
2.an existing method in the test class
4.When more methods belong together extract them into a new class
5.Refactor as required
by Adi Bolboaca