My talk about the history of TDD and the discussions about its positive and negative aspects on software development. Held on Frankfurter Entwicklertag 2017.

1. TDD is for Dreamers,
not for Real Developers,
Isn’t It?
Sven Amann
academicscode.com
letsdeveloper.com
@svamann
artwork by Sven Amann - CC BY-SA 4.0

2. Why do I talk about TDD?
Why TDD
(discussions)?
artwork by Sven Amann - CC BY-SA 4.0
Sven Amann

3. artwork by Sven Amann - CC BY-SA 4.0
Academics code
Physicist
Computer
Scientist

4. artwork by Sven Amann - CC BY-SA 4.0
A Pro

5. Introduction to Computer
Science I - WS06/07
artwork by Sven Amann - CC BY-SA 4.0

6. “Faster development, higher code quality,
better design, and less waste!” Kent Beck
“Self-testing code and clean
interfaces!” Martin Fowler
“Exhaustive test suites, close to no
debugging, changing code without
fear, reduced coupling, …” Uncle Bob
“Fast feedback and safe
refactoring” James Shore

7. Academics code
artwork by Sven Amann - CC BY-SA 4.0

8. Academic
Industry
Developer
artwork by Sven Amann - CC BY-SA 4.0

9. Academic
Industry
Developer
artwork by Sven Amann - CC BY-SA 4.0

10. Academic
Industry
Developer
artwork by Sven Amann - CC BY-SA 4.0

11. “TDD is dead. Long live testing” DHH
“TDD needs a funeral.” Cope
“The real "problems" with TDD [is] in the "driven"
part, not the "test" part [and] the zealotry of
some of its evangelists” Rich Hickey

12. ?!?
artwork by Sven Amann - CC BY-SA 4.0

14. Agile Alliance TDD
1976: The Dark Age of Developer Testing
“a developer should never test their own code”
Glenford Myers in “Software Reliability”
1994 - Kent Beck develops SUnit
1999 - Kent says “test first” in “XP Explained”
until 2002 - “test first” evolves to “test driven”
Source: https://www.agilealliance.org/glossary/tdd/

15. Queueing Theory
Source: http://blog.jbrains.ca/permalink/how-test-driven-development-works-and-more

16. Test-first Programming
Source: http://blog.jbrains.ca/permalink/how-test-driven-development-works-and-more

17. Uncle Bob’s Three Laws of TDD
1. You are not allowed to write any
production code unless it is to make a
failing unit test pass.
2. You are not allowed to write any more
of a unit test than is sufficient to fail;
and compilation failures are failures.
3. You are not allowed to write any more
production code than is sufficient to
pass the one failing unit test.
Source: http://butunclebob.com/ArticleS.UncleBob.TheThreeRulesOfTdd

18. Classic
TDD

19. Classic
TDD Test: 1 = “I”
return “I”;
Test: 2 = “II”
return (i == 1) ? “I” : “II”;
Test: 3 = “III”
return i * “I”;
...

20. Classic
TDD
• Roman Numbers
• FizzBuzz
• Bowling Game
• Game of Life
• Harry Potter Book Sets
• …
Algorithms with
well-defined input-output relation

21. Test!
!Test
artwork by Sven Amann - CC BY-SA 4.0

22. –John Sonmez
“By writing unit tests ... you find all kinds of
problems with that code ... of those units [but]
unit testing is more of an appraisal activity than
a testing one... very few regressions are caught
by unit tests since changing the unit of code
you’re testing almost always involves changing
the unit test itself.”

23. Table 3-25, p. 179

24. Developer Test
≠
Acceptance Test
artwork by Sven Amann - CC BY-SA 4.0

25. “a developer should never test their own code”
–Glenford Myers
artwork by Sven Amann - CC BY-SA 4.0
self
control

26. Developer tests
are our job!
artwork by Sven Amann - CC BY-SA 4.0

27. Test
Test B
Test
Waste
Valuable
Tests
artwork by Sven Amann - CC BY-SA 4.0
TDD Tests

28. Required Functionality
All It Can Do
artwork by Sven Amann - CC BY-SA 4.0
Waste

29. Toy Project Real Software
???

30. Test-driven Programming
Source: http://blog.jbrains.ca/permalink/how-test-driven-development-works-and-more

31. London School TDD

32. London School TDD
Source: http://coding-is-like-cooking.info/tag/london-school-tdd/

33. ???
Sale
Catalog
Display
Acceptance Test: “Sell One Item”

34. –James O. Coplien (Cope)
“TDD was created to replace up-front
architecture. It is not a testing technique.”
Source: https://twitter.com/jcoplien/status/828291686128304130

35. class Person
def age
Date.today.year - birthday.year
end
end
test “a person’s age is determined by birthday” do
seventy_niner = Person.new birthday: Date.new(1979)
travel_to Date.new(2009)
assert_equal 30, seventy_niner.age
end

36. artwork by Sven Amann - CC BY-SA 4.0
class Person
def age(now = Date.today)
now - birthday.year
end
end
test “a person’s age is determined by birthday” do
seventy_niner = Person.new birthday: Date.new(1979)
assert_equal 30, seventy_niner.age Date.new(2009)
end

37. First Design,
then Code,
then Test.
That’s how
we’ve always
done it.
artwork by Sven Amann - CC BY-SA 4.0
Traditional
Waterfall
Testing
Agile
Over-Enthusiast
All but that…

38. –David Heinemeier Hansson (DHH)
“Writing software is more like writing french
poetry than a hard science.”

39. The Ultimate Design
(You’ll Never Need)
artwork by Sven Amann - CC BY-SA 4.0

40. –Joe Rainsberger (jbrains)
“TDD doesn't create design. You do.”

41. Check Your Own Work Cleanup After Your TDD
Remember To Think
Listen Closely &
Consider the Context

42. –Joe Rainsberger (jbrains)
“TDD Is Not Magic. The rules themselves do not
guarantee success. You have to keep the brain
switched on. You have to pay attention to what’s
happening. You need a place to ask questions
and get answers. You need to know that when you
practise TDD, your code starts to speak to you,
but in a language you [may not yet] understand,
and that when you write tests and run them, this
act equates to learning a language by hearing it,
trying to speak it, and by native speakers
correcting you. If you do these things, then I
expect TDD to “work” for you.”

43. Sven Amann
academicscode.com
letsdeveloper.com
youtube.com/letsdeveloper
@svamann
artwork by Sven Amann - CC BY-SA 4.0