Have you heard of TDD? Are you interested or familiar with this practice but have never been able to understand it? Join this session to see the benefits of Test-Driven Development (TDD), understand how it works and its benefits. In a more detailed approach, we will see this way of developing software, where our code is always built guided by tests. We will go over some history about TDD, which is the main process we must follow when we work with this mechanic and the rules that surround it. We will also list the main advantages and disadvantages that most developers who practice TDD find and whether the arguments in favour add up to more than those that subtract. Finally, we will review some good habits and practices when applying TDD and see how to do it step by step with an example of a "live" coding session with Java. At the end of the session, I hope that you will have a wider understanding of what TDD is, what advantages it brings, why it is interesting to master it and also that you will take with you some tricks and good practices to be able to apply them in your day-to-day life when writing code === Presentation (revisited & updated) shared at JDD 2022: https://jdd.org.pl/lecture_2022/#id=78434

1. TDD: seriously, try it ! 😃
JDD 2022

2. First thing first

3. • Review the basics around TDD
• Understand the benefits of
building code designed by tests
VS
building the tests after we write
our code
• See an example
• (I hope) learn some tips
• … so do not run away, please!
😉
Why this session?

4. Nacho Cougil
• Principal Software Engineer at
Dynatrace
• TDD & clean code fan
• Started to write in Java before Y2K
• Founder of the Barcelona Java Users
Group ( BarcelonaJUG ) & co-
founder of the Java and JVM
Barcelona Conference
( JBCNConf  DevBcn )
• Father, former mountain marathon
runner 😅
• @icougil
Who am I?

5. Based on my
*personal*
experience
Warning

6. • Where it cames from?
• Advantages &
disadvantages
• Process
• Good habits
• Example
• Final Recap
Agenda

7. • Where it cames from?
• Advantages &
disadvantages
• Process
• Good habits
• Example
• Final Recap
Agenda

8. Kent Beck “rediscovered” TDD
when writing first testing
framework SUnit in 1994.
TDD became part of eXtreme
Programming (XP) book in
2000. Developed XP during his
work at Chrysler
The book Test-Driven
Development by Example was
published in 2002
A bit of history

9. Mockist (London)
• Entry point: acceptance test
• Design from top down
• Main focus on the
interactions between the
components of our solution
• Focus on messages we will
use with our classes. Here is
where mock objects appear
Classical (Chicago)
• Described by Kent Beck
• More emphasis on “discovering” the
internals of our code mainly by
refactoring
• The structure of our classes and
modules emerges as we evolve our
code (ex: removing duplication,
encapsulation, etc)
• Focused on changes in an state or
return values from functions
Two TDD
schools

11. … you follow a simple process ⚙️
that helps you to design and
develop your software in a
straightforward way
… you can find defects earlier ⏱
(when running or designing your
tests)
… you can easily detect
regression errors 🔴
… your software is going to be
easier to refactor because of a
safety net ✅
Imagine…

12. ... your software guides you how a
consumer will use your component ⏛
… tests are living documentation (really
🖖 !!)
… the software you write it is likely to
have less bugs 🐛
… your development costs 💰 will be
lower
References:
- Test-driven development as a defect-reduction practice
(IEEE)
Imagine…

13. It is not so easy to start with 😅
(not many good places to help, majority
of people are not using it daily)
Has a high learning curve 😟
(depends directly on the complexity of
your code + your design and
engineering capabilities)
Can be a large investment 💸 in a
team (depending on the experience of
the members + requires time ⏳ & effort
🙇♀️🙇♂️)
Yes, TDD has some disadvantages

14. It is really easy to forget 😓 about it
It provokes resistance ☹️ (in some
people ⚔️)
Can be corrupted and lead to the
syndrome of reaching the highest
possible level of coverage 🙈
It is extremely difficult 😤 to master at it
Yes, TDD has some disadvantages

16. You learned how to write code time
ago,…
…and now you’d may learn a different
way of writing software. Like “learning
to ride a very different bike”,... but being
So, … how it is?

17. To be used in your design &
coding process , for
building better modularized
and tested software
And, what does it
seek?

18. • Where it cames from?
• Advantages &
disadvantages
• Process
• Good habits
• Example
• Final Recap
Agenda

19. The process

20. • Where it cames from?
• Advantages &
disadvantages
• Process
• Good habits
• Example
• Final Recap
Agenda

21. Start little by little: katas, POCs,
personal projects, ...
Practice...
• ... and keep practicing
• ... and keep on
• ... until you finally internalise it 🖖♀️😉
Practice with somebody else
( pair-programming )
Keep learning: online content, books,
...
Learn and practice

22. An Extreme Programming (XP)
Practice in which 2 developers participate
in one development effort at one
workstation.
One, the driver, writes code while the
other, the navigator or observer,
reviews the code as it is typed in. The 2
engineers switch roles frequently.
While reviewing, the observer also
considers the "strategic" direction of the
work, coming up with ideas for
Pair programming

23. Martin Fowler (concepts)
• https://www.martinfowler.com/bliki/TestDouble.html
• https://martinfowler.com/articles/mocksArentStubs.h
tml
• https://martinfowler.com/articles/practical-test-
pyramid.html
Dave Farley (CI, TDD, etc)
• https://www.youtube.com/ContinuousDelivery/
James Shore (TDD series)
• https://www.youtube.com/jdlshore/
Jason Gorman (Java Code Craft)
• https://www.youtube.com/parlezuml/
Recommended
content

24. Before you write production code,
check 👀 that your test is failing 🔴
Each test has only 1 reason to fail
Write the assertion first
Technical good habits

25. Tests naming convention
Describe the
expected
behaviour, not
the internals.
Our tests
should
describe
behaviour in
plain english
Ending the class name
with Should will “force “
you to start describing
an action for every test
you may create

26. Our tests methods will only describe
behavior. Therefore, we will have a
better understanding on what this class
does
Our tests will be more clear
If some tests fails, we can have a look
and see easily which case is failing
We don’t need to get into details on
any test to understand what are they
pursuing
The result will be focused on the
business

27. Test creation order
1) Name the
class
2) Name
the method
3) Define what you want to
check
4) Trigger the code
5) Do the setup

28. • Where it cames from?
• Advantages &
disadvantages
• Process
• Good habits
• Example
• Final Recap
Agenda

29. Warning – Live coding!

30. Requirements:
• Build a service that returns a list of films
that are associated with a particular genre
• By default, the result must be ordered
according to the average rating given to the
films by the users
• A film should contain at least an id, title a
year when it was published, one or more
tags and one or more genres
Example:
recommendationService.filmsByGenre(”science-
fiction”)
https://github.com/icougil/FilmRecommendationService
We have just started working in a startup
that sells and rents out films over the
Internet
Our product managers have told us that
they want to add new functionalities by
building a service that allows them to
recommend films to the users of the
current platform.
Kata: Film Recommendation Service

31. • Where it cames from?
• Advantages &
disadvantages
• Process
• Good habits
• Example
• Final Recap
Agenda

32. • TDD helps you to design & develop
your code in a simple and effective way
(better modular design) 👌
• It is difficult to adapt to its mechanics
and sometimes is difficult 😅 to maintain
its practice...
• It worth a try 😉 (your software will have
less bugs 🐛 & it will be easier to
maintain 💰)
• There are some tips 💡
( could make your life easier )
• Try to pair, it will help 😃 you ( a lot )
• Practice, practice & practice 🖖 again
Final Recap

33. Questions?
nacho@cougil.com
https://nacho.cougil.com
@icougil