Gib dem Entwickler seine Code Kata!

What the heck is

Software Craftsmanship?

 Benjamin Nothdurft

 Sandra Parsick

2019-05-21 at

Magdeburger Developer Days 2019

Benjamin Nothdurft


Sandra Parsick






Brief History

Current State

Dojo & Katas

Disclaimer: Thanks to our fellow crafters!

@MarcoEmrich / @DavidVoelkel

Brief History

Software Development

Today we know software development is a mixture out of craft, research and engineering!

However it was not always like this...


  • Idea in the 90s: software factories for automated software development
  • First try: Engineering as craft!

2001 - Birth of Agile

  • Agile reaches from Scrum (project view) to XP (technical view)
  • Focuses however strongly on project process!
  • Technical excellence largely neglected.

2008 - Agile Hangover

Keynote from Uncle Bob:

  • 5 principles to "craftsmanship over crap"

...later transformed to:

  • craftsmanship over execution

2009 - Manifesto for SC

2002 - Software Apprenticeship Summit:

  • no outcome!

2008 - SC Summit: Micah Martin gave a session

  • many ideas as outcome
  • whiteboard was signed by everyone

2009 - Doug Bradburry wrote in SC Google group "The New Left Side" vs. Scott Pfister "Right Side, Revisited"

 Why a manifesto?

  1. vocal community
  2. create visibility
  3. establish principles
  4. develop schools
  5. guidance for new devs

2014 - The Software Craftsman

  • Ideology and Attitude
    • History
    • Professionalism
    • Practises
    • ...
  • Full Transformation
    • Recruitment
    • Interviews
    • Culture
    • Pragmatism
    • Career

Current State

2009 - First SC conferences in USA, UK

2009 - Israeli SCC was founded

2010 - London SCC was founded

2011 - First SoCraTes in Germany


Today - SoCraTes (partner) conferences/days in:


Germany, Chile, Canaries, Italy, UK, USA, Switzerland, France, Austria, Belgium, Finnland, Romania...


SCC Communities

  • 328 groups
  • 138k on

  vs. 1,5M with Agile

Communities in DACH region


  • 29 regional groups
  • 2k on website
  • 9k on


..but we need to go back to the roots!

  • many new aspiring devs

  • principles got lost again down  the road while doing other activities

  • IT market is booming and we need technical excellence to tackle our software products

  • arising lack of broad TDD knowledge

Dojo & Katas

Craftsmanship Principles

Individuals & Interactions

(Learning from each others)

Clean Code

Lifelong Learning

Continuous Improvement


What is a coding dojo?

A bunch of coders get together, code, learn, and have fun. It’s got to be a winning formula!  ​– Emily Bache

Why do we need a coding dojo?

  • no managers, no deadlines
  • safe environment
  • all professionals need to practice!
  • not all forms of practice are equal
  • special way to practice
  • designed to emphasize skills that are hard to aquire and easy to lose!

Coding Dojo Principles

  • First Rule: Design cannot be discussed without Code, Code can not be shown without tests.

  • Come with your relicts

  • Learning Again

  • Slow down

  • Throwing yourself in

  • Finding a master

  • Subjecting to a master

  • Mastering a subject

  • Kata: a Japanese word, meaning literally: "form" (型 or 形), is a detailed choreographed pattern of movements made to be practiced alone, but are also practiced within groups and in unison when training!
  • In Karate: A kata is an exercise where you repeat a form many, many times, while making little improvements in each repetition!

 What do we practice?

Characteristics of a Code Kata

  • Definition: A kata is a defined solving flow of a code exercise made to be practiced many, many times alone, in pairs or as groups (e.g. MOB Programming) while making little improvements.
  • Duration: Most exercises are quite short (~ 30 minutes to 1 hour) so that one can incorporate them as routines in daily life!
  • Content: Some involve programming, and can be coded in many different ways. Some are open ended, and involve thinking about the issues behind programming, e.g. architecture katas.
  • Focus: The point of the kata is not arriving at a correct answer. The point is the stuff you learn along the way. The goal is the practice, not the solution!

TDD is used as a default pattern for coding!

FizzBuzz Kata


  • Write a program that prints the numbers from 1 to 100 but:
  • ...for multiples of 3 print Fizz
  • ...for multiples of 5 print Buzz 
  • ...for multiples of both 3 and 5 print FizzBuzz


  • 1, 2, Fizz, 4, Buzz, Fizz, 7, 8, Fizz, Buzz, 11, Fizz, 13, 14, FizzBuzz, 16, 17, Fizz, 19, Buzz, Fizz, 22, 23, Fizz, Buzz, 26, Fizz, 28, 29, ...

first described in the essay "Fizz! Buzz!” (~1987) by David Langford as a drinking game of his teenage years in the 1960s

...more selected Katas

  • String Calculator Kata

  • Bowling Game Kata (by Robert C. Martin)

  • Prime Factors Kata (by Robert C. Martin)

  • Diamond Kata by Seb Rose

  • BankOCR Kata

  • Ordered Jobs Kata

  • Roman Numerals Kata

  • Kebab Kata

  • Game Of Life

  • ...

How do I facilitate a dojo meeting?


  • Book a room, Invite people, Print copies of kata description, prepare some slides for dojo introduction, inspect the chosen kata upfront


  • Line people up by experience and match people with the most with the ones with lowest etc. (folding queue)


  • Facilitator needs to create good/healthy atmosphere, prompt interesting discussions, keep the code growing,

  • Try not stop people when they mess up with TDD, let them learn from mistakes, wait until retro before saying anything!

09:30 Intro/Talks

10:45 Round 1

11:45 Round 2

12:45 Lunch

13:30 Round 3

14:30 Round 4

15:30 Round 5

 Code Retreat Day

A format popularized by Corey Haines

45" code + 10" retro + 5" break

Kent Beck:

  • passes all tests
  • maximizes clarity/intention
  • minimizes duplication (DRY)
  • has fewer elements


  • Basic Activities

    • Ping Pong

    • Navigator-Driver

  • Missing Tool Activities

    • No Mouse

    • Text Editor only

    • Paper only

  • Missing Feature Activities

    • No naked primitives

    • No conditional statements

    • No loops

  • Quality-Constraint Activities

    • Only four lines per method

    • Immutables only, please

  • Stretch Activities

    • Verbs instead of Nouns

    • Code Swap

    • Mute with find the loophole

    • TDD as if you meant it

...more Constraints

  • Baby Steps

  • Silent Coding (Mute)

  • No If

  • No IDE

  • No Mouse

  • Only One-Liners

  • Every Cell is a Microservice (at Game of Life)

Discussion points for retro

  • Did you ever write more code than you needed to make the current tests pass?
  • Did you ever have more than one failing test at a time?
  • Did the tests fail unexpectedly at any point? If so, why?
  • How much did writing the tests slow you down?
  • Did you write more tests than you would have if you had coded first and written tests afterwards?
  • Are you happy with the design of the code you ended up with? Should you have refactored it more often?



 Sandra Parsick

 Benjamin Nothdurft


TDD & Clean Code

What is TDD? Why is it so hard?

  • TDD is not about testing!
  • TDD = specs/design
  • QA is minor point
  • TDD is living documentation
  • Isolation, Focus
  • Test new behaviour in babysteps


  • Higher dev speed
  • Better code quality
  • Patterns: AAA

Different TDD schools

  • London School (Mockist)

    • Double Loop ATDD

    • Outside-In Design

  • ​Detroit School (Classicist)

    • Kent Beck, Uncle Bob...

    • front-door testing

    • state verification

    • only mock the process boundary (DB, 3rd party)

    • design emerges bottom-up / inside-out

    • "TDD as if you meant it"

  • "Munich School"

    • ​Fake-it Outside-In Design

"TDD as if you meant it"

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.

Three rules by Robert C. Martin / Keith Braithwaite

SOLID Principles

by Robert C. Martin / Acronym by Michael Feathers

  • Single responsibility (SRP) "a class should have only a single responsibility​"
  • Open/closed "software entities... should be open for extension but closed for modification"
  • Liskov substitution "objects should be replaceable with instances of their subtypes without altering the correctness of that program"
  • Interface segregation "many client-specific interfaces are better than one general-purpose interface"
  • Dependency inversion "depend upon abstractions, not concretions"

Other Principles

  • KISS - "keep it simple, stupid"
  • DRY - "Don't repeat yourself"
  • YAGNI - "You aren't gonna need it"
  • DTSTTCPW - "Do the simplest thing that could possibly work"
  • ...
  • ...
  • ...

...and many more principles can be practiced with Katas!

Game of Life (Video)

Life in life!



Brief History - 10"

Current State - 5"

Dojo & Katas - 25" 

Clean Code - 5" 

Disclaimer: Thanks to our fellow crafters!

@MarcoEmrich / @DavidVoelkel


Roman Numerals Kata


  • Write a method String convert(int) that takes a number and converts it to the according String representation.



  21 ➔ XXI
  50 ➔ L
 100 ➔ C
 500 ➔ D
1000 ➔ M


   1 ➔ I
   2 ➔ II
   3 ➔ III
   4 ➔ IV
   5 ➔ V
   9 ➔ IX

1. Create a simple String calculator with a method int add(string numbers)

  • can take 0, 1 or 2 numbers and will return their sum, e.g. “” or “1” or “1,2”
  • Start with the simplest testcase of an empty string and move to 1 and 2 numbers
  • Remember to solve things as simply as possible
  • Remember to refactor after each passing test

2. Allow the add method to handle an unknown amount of numbers

3. Allow the add method to handle newlines between numbers instead of commas.

4. Support different delimiters with pattern: //[delimiter]\n[numbers...] , e.g. “//;\n1;2”

5. Calling add with a negative number should throw an exception “negatives not allowed”

6. Ignore big numbers, e.g. boundary is 1000 then 1001 + 2 = 2


Idea by Roy Osherove

String Calculator Kata (Video)

Steps 1. + 2. = Solved with preparatory refactoring


Clean Code


Benjamin Nothdurft


SCC Communities

  • 328 groups
  • 138k on

Clean Code Helsinki

Latvian SCC


  vs. 1,5M with Agile

Diamond Kata by Seb Rose

Given a letter print a diamond starting with 'A' with the supplied letter at the widest point on the command line.


Example for B

Example for C

Example for E

Diamond Kata (Video)

Fake-it-inside-Out Approach

Made with