Have you heard of TDD? Are you interested or familiar with this practice but have never been able to understand it? In this presentation we will see the benefits of Test-Driven Development (TDD), understand how it works and what the benefits are of using it. We will see in a more detailed approach this way of developing software, where our software 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 "live" coding session with Java. At the end of the session, we 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 

1. TDD: seriously, try it ! 😃

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First thingfirst

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Whythis session?
• Understand the basics around TDD
• Be able building a software starting with tests
• Understand the benefits of building code
covered by tests
VS
building the tests after we write our code
(before VS after)
• Code a bit (and probably) learn something
new from your colleagues
• … so do not run away please! 😉

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NachoCougil
• Senior Software Engineerat Dynatrace
• TDD &cleancode fan
• Started to write in Javabefore the effect 2000
• Founderof the Barcelona Java Users Group &
co-founderof the Java and JVMBarcelona Conference (JBCNConf)
• Father, formermountain marathonrunner 😅
@icougil
WhoamI?

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• Raise yourhand at anymoment!
Askquestions atanytime,please!

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Warning
Basedon my*personal*experience

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• Whereit camesfrom?
• Advantages & disadvantages
• Process &rules
• Good habits
• Questions?
• Demo
• Pair programming
• Kata
• Final Recap
Agenda

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• Where it cames from?
• Advantages & disadvantages
• Process &rules
• Good habits
• Questions?
• Demo
• Pair programming
• Kata
• Final Recap
Agenda

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• Kent Beck “rediscovered” TDD whenwriting first
testing framework SUnitin1994.
“Taketheinputtape,manuallytypeintheoutput
tapeyouexpect, then programuntiltheactual
outputtapematches the expected output.”
• TDD became part of Extreme Programmingbook
in1999.
Abit of history

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• … youcan find defects earlier ⏱ (when runningor
designing yourtests)
• … youcan easily detect regression errors 🔴
• … youfollow a simple process ⚙️ that helps youto
develop yoursoftware in a straightforward way
• … yoursoftware is going to be easier to refactor
because of ✅ green (safety net)
For a moment,imagine…

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For a moment,imagine…
• ... yoursoftware guides youhow a consumerwill use your
component ⏛
• … tests are living documentation (really 🖖 !!)
• … the software youwrite it is likely to have less bugs 🐛
• … yourdevelopment costs 💰 will be lower
References:
- Test-drivendevelopmentasa defect-reductionpractice(IEEE)
- GuestEditors' Introduction:TDD--TheArt of FearlessProgramming (computer.org)

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Yes,TDDhassomedisadvantages
• It is not so easy to start with 😅
(not manygood places to help, majority of people are not using it
daily)
• Has a highlearningcurve 😟
(depends directly on thecomplexity of yourcode + yourdesign
and engineeringcapabilities)
• Can be a largeinvestment 💸 in a team (depending on the
experience of the members + requires time ⏳ &effort 🙇♀️🙇♂️)

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• It is reallyeasy to forget 😓 about it
(especiallyifyou arenot inan environment/ teamthat
does not encourageits use or you cannot experiment
withitcomfortably)
• It provokesresistance☹️ (in somepeople)
• Can be corrupted and lead to the syndromeof reaching
the highest possible levelof coverage 🙈
• It is extremelydifficult 😤 to masterat it
Yes,TDDhassomedisadvantages

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So,… how it is?
• Youlearnedhow to write code time ago,…
• …and now you’dmay learn a different way of writing software.
Like“learningto rideaverydifferent bike”,... but being older 😅

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• Whereit camesfrom?
• Advantages & disadvantages
• Process &rules
• Good habits
• Questions?
• Demo
• Pair programming
• Kata
• Final Recap
Agenda

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Theprocess

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 Focus on building tests first that will help us demonstrate the
behaviour we want.
 Wewill start writing tests and we can’t writeverymuchapart
from a unittest. Tests are first class citizens
 No overengineering, simple code, simple solution: makethe test
pass
• You are not allowed to writeany production code unless it is to
makea failing unit test pass.
• Youare not allowed to write any more of a unit test than is
sufficient to fail.
• Youare not allowed to write any
more production code than is
sufficient topass the one failing
unit test.
Robert C. Martin
(uncleBob)
Therules

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• Whereit camesfrom?
• Advantages & disadvantages
• Process &rules
• Good habits
• Questions?
• Demo
• Pair programming
• Kata
• Final Recap
Agenda

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• Before you write production code,
check that your test is failing 🔴!
• Each test has only 1 reason to fail
• Write the assertion first
Goodhabits

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Tests namingconvention
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

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• Ourtests methods will only describe behavior.
Thereforewewill havea better understanding on
what this class does
• Ourtest will be moreclear
• If some tests fails, we can havea look and see
easily which case is failing
• Wedon’t need to get into details on anyparticular
test if wedon’t need it
Theresult will befocusedonthe business

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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

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• Startlittleby little...
• Katas
• Proofs of concept
• Personal projects
• Practicewithsomebody else (pair-programming)
• Practice...
• ... and continues to practice
• ... and continues
• ... until you finally internalizeit 🖖♀️
• Checkonline content
But, howto start?

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• Whereit camesfrom?
• Advantages & disadvantages
• Process &rules
• Good habits
• Questions?
• Demo
• Pair programming
• Kata
• Final Recap
Agenda

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Questions?

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• Whereit camesfrom?
• Advantages & disadvantages
• Process &rules
• Good habits
• Questions?
• Demo
• Pair programming
• Kata
• Final Recap
Agenda

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Warning –Live coding!

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Demo/ Kata 1:FizzBuzz
• https://kata-log.rocks/fizz-buzz-kata • Write a program that prints one linefor each numberfrom 1 to
100
• For multiples of 3 print Fizzinstead of the number
• For the multiples of 5 print Buzzinstead of thenumber
• For numberswhich are multiples of both 3 and 5
print FizzBuzzinstead of thenumber

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• Whereit camesfrom?
• Advantages & disadvantages
• Process &rules
• Good habits
• Questions?
• Demo
• Pair programming
• Kata
• Final Recap
Agenda

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• An ExtremeProgramming(XP)Practicein which2 developersparticipate inone
developmenteffort at one workstation.
• One,the driver,writescode whilethe other, the navigator orobserver,reviewsthe
code as it istyped in. The 2engineersswitchrolesfrequently.
• While reviewing,the observeralso considers the "strategic"direction of the work,
coming up with ideas for improvementsand likelyfuture problemsto address.This is
intended to freethe driverto focus all of their attention on the"tactical" aspectsof
completingthe currenttask, using theobserveras a safety netand guide.
Pair programming

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• Theprocess is:
1. One person (A) writes a newtest and verifies that it fails 🔴
2. Theother developer (B) implements the code needed to pass the test ✅
3. (optional) -Theother developer (B) decides to refactor part of the code
4. Theother developer (B) writes thenext test and verifies that it fails 🔴
5. Thefirst developer (A) implements thecode needed to pass thetest ✅
Ping-pongpairprogramming

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Thinkaboutcraftmanship
• Be patience, don’t rush.
• Tryto learn as muchas youcan from your colleague
• No pair pressure -> negotiation for the win!
• Write code youwill be proud of 😃👍

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Be kind and respectful

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Are youready?

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Let’s play!

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Kata:Leap year
• As a user, I want to know if a yearis a leap yearor not. • All yearsdivisible by400are leap years (so, for example, 2000
was indeed a leap year),
• All yearsdivisible by100but not by 400 are NOTleap years (so,
for example, 1700,1800,and 1900were not leap years, NORwill
2100bea leap year),
• All yearsdivisible by 4but not by100are leap years (e.g., 2008,
2012,2016),
• All yearsnot divisible by4 are NOT leap years (e.g. 2017,2018,
2019).

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Kata:String calculator
• Createa simple String calculator with a method signature:
int Add(string numbers)
• Themethod can takeup to two numbers, separated by commas,
and will returntheir sum.
Examples:
• “” or “1” or “1,2” as inputs.
• For an empty string it will return0.

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Kata:String calculator
• Iteration 1
Allow theAdd method to handle an unknownamountof
numbers.

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Kata:String calculator
• Iteration 2
Allow theAdd method to handle newlinesbetween numbers
(instead of commas).
Examples:
• Thefollowing input is ok: “1n2,3”(will equal 6)
• Thefollowing input is NOTok: “1,n” (not need to proveit -just
clarifying)

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Kata:String calculator
• Iteration 3
Support different delimiters:
• To change adelimiter, the beginning ofthe string will contain a
separate line that looks like this: “//[delimiter]n[numbers…]” for
example “//;n1;2” should return three where the default delimiter
is‘;’.
• The firstline is optional. All existing scenarios should still be
supported.

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Kata:String calculator
• Iteration 4
Calling Add with a negative numberwill throw an
exception “negatives not allowed” -and the negative that was
passed.
• If there are multiple negatives, show all of them in the exception
message.

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Kata:String calculator
• Iteration 5
Numbersbigger than 1000should be ignored.
• Ifyou want more,you can playmore!See: https://kata-
log.rocks/string-calculator-kata
Example:
• 2+ 1001= 2

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• Whereit camesfrom?
• Advantages & disadvantages
• Process &rules
• Good habits
• Questions?
• Demo
• Pair programming
• Kata
• Final Recap
Agenda

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• Martin Fowler (main concepts around testing)
• https://www.martinfowler.com/bliki/TestDouble.html
• https://martinfowler.com/articles/mocksArentStubs.html
• https://martinfowler.com/articles/practical-test-
pyramid.html
• JamesShore(JS practices)
• https://www.youtube.com/user/jdlshore/videos
• Jason Gorman(Java practices)
• https://www.youtube.com/user/parlezuml/videos
Recommendedcontent

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• TDD helpsyouto develop yourcode in a simple and effective way
👌
• It is difficult to adapt to its mechanicsand sometimes is difficult 😅
to maintainits practice...
• Itworth a try 😉 ( yoursoftware will haveless bugs 🐛 & it will be
easier to maintain 💰 )
• Thereare some tips 💡
( could makeyourlife easier )
• Tryto pair, it will help 😃 you (a lot )
• Practice, practice &practice 🖖 again
FinalRecap

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nacho@cougil.com
https://nacho.cougil.com
@icougil
Questions?
I need yourfeedback, please:
https://bit.ly/tdd-seriously-try-it-feedback

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