Test Driven Development Intro and demonstration. Delivered at Christchurch Agile Professionals Network on 31 May 2012

1. Test Driven Development
Demonstrated
Alan Christensen @christensena
Tom Gutteridge @trgutteridge
A g ile P r o f e s s io n a ls N e t w o r k
C h r is t c h u r c h
Th a n k s to o u r s p o n s o r s …

2. 2

9. Who am I?

10. Format
• Introduction Presentation
• Live coding exercise
• Review slides
• TDD in the real world
• Questions and discussion

11. Test Driven
Development
• It is a development technique
• Incremental (iterative) workflow
• Always write a failing test
first (red)
• Only write the minimum
code to pass the failing test
(green)
• Improve code while all tests
are passing (refactor) http://www.agileapps.co.uk/methodology/continuous.html

12. Not about testing #1
• Yes you do end up with a suite of tests
• But TDD is a development exercise
• my mindset is coding, not testing
• I will not be exhausting edge cases, etc
(at least initially)

13. Not about testing #2
• By practicing TDD
• I approach my code from the outside,
focusing on specifying behaviour
• I can focus on one thing at a time
• My resulting code is inherently designed
for testability
• I get fast feedback

14. Live coding exercise
• Coding Kata
• Wikipedia definition: “A code kata is an
exercise in programming which helps hone
your skills through practice and repetition”

15. TDD improves design
• Encourages separation of concerns/single
responsibility principle (SRP)
• Incremental, iterative: can lead to simpler
designs
• Reduces fear of refactoring, encouraging
improvements to design
• Alerts me to design smells

16. Tests as documentation
• Unit test code provides numerous working
examples of API usage
• Good unit test structure and naming can
act as a specification
• Tests as documentation always up to date
(or the tests are failing)

17. Objections to TDD
• It takes too much time
• Tests can make it harder to refactor, not
easier
• It’s just too hard with our legacy code or
un-mockable framework(s)
• Our test suite takes too long to run so we
don’t run it very often

18. Why is TDD Hard?
• Mindset seems unnatural at first
• Many frameworks/library components
make it difficult to verify behaviour
• Large monolithic blocks of legacy code are
hard to isolate
• Good design is not always obvious at first
• Forgetting to test first, not afterwards!

19. Make TDD easier
• Practice Red-Green-Refactor discipline on
simpler examples (e.g. katas) away from a
real code base
• Learn from each other (e.g. weekly brown
bag/dojo sessions), pair programming
• Learn good design, especially OO design
• Listen to your tests! If it’s getting hard
going, consider refactoring your code
• Take it seriously!

20. Tips: Untestable
Frameworks
• Use adapter pattern to "broker" untestable
dependencies
• Adapters should be tailored to how they
are used by the app. Adapters do not need
to expose entire API, only what is needed
• Decouple logic from frameworks (e.g. use
MVC pattern)

21. Productivity with TDD
• It takes practice to become productive
• Test code should be taken seriously, not
treated as throwaway
• Keep duplication to a minimum but balance
this with readability
• Worst case: your design completely
changes resulting in rewrite. You have the
old tests as a reference (specs)

22. What not to TDD?

23. What is a unit?
• "smallest thing that makes sense" George
Dinwiddie
• Sometimes a method, sometimes a
collaboration of classes

24. Unit vs Integration
• Unit tests
• should be fast (fast feedback loop)
• should be focused
• when they fail, they usually point you to
where problem is
• rigorous within the component under
test
• one assert per test

25. Integration vs Unit
• Integration tests
• usually slow
• good for verifying unit tested
components connect together properly
• good for acceptance tests
• often easier to start with on a legacy
code base

26. Other Topics
• System Under Test isolation (mocks and
stubs)
• Real World Unit Testing (or how to deal
with existing test unfriendly code)
• Context specification (or how to write
expressive, DRY test suites)
• Tips and Tricks, avoiding anti-patterns

27. Links
• String Calculator kata exercise
http://osherove.com/tdd-kata-1/
• Bowling game kata step by step
(Powerpoint)
http://butunclebob.com/ArticleS.UncleBob.TheBow