The slides of my "Transformation Priority Premise" Session at the Softwerkskammer Munich Meetup.

1. The Transformation
Priority Premise
Softwerkskammer Meetup Munich
11.02.2016
David Völkel

2. Agenda
● Pizza
● Theory
● Kata
● Another Beer

3. Problem
Stuck with TDD
Too much to implement in one test
Image by Thor

4. Solution
Take Baby Steps
Image by Seattle Municipal Archives

5. What to choose next?
Simple to Complex
● What is the most simple
implementation?
● Uncle Bob‘s guideline: the
„Transformation Priority Premise“

6. Test Driven Development
red
refactor
green

7. Types of Code
Testcode
red
refactor
green
„Transformation“
= Implementation
Refactoring
Design

8. Transformation Priorities
● ({}–>nil) no code at all -> code that returns nil
● (nil->constant)
● (constant->constant+) simple to a more complex constant
● (constant->scalar) replacing a constant with a variable
● (statement->statements) adding more unconditional
statements
● (unconditional->if) splitting the execution path
● (scalar->array)
● (array->container)
● (statement->recursion)
● (if->while)
● (expression->function)
● (variable->assignment) replacing the value of a variable.

9. Strategy
• When passing a test, prefer
higher priority
transformations
• Choose as next test the one
that can be implemented
with higher priority
transformations
green
refactor
red

10. Strategy
• When passing a test, prefer
higher priority
transformations
• Choose as next test the one
that can be implemented
with higher priority
transformations
• Even during refactoring
green
refactor
red

11. The Kata
Transformation priorities:
● ({}–>nil) no code at all -> code that returns nil
● (nil->constant)
● (constant->constant+) simple to a more complex constant
● (constant->scalar) replacing a constant with a variable
● (statement->statements) adding more unconditional
statements
● (unconditional->if) splitting the execution path
● (scalar->array)
● (array->container)
● (statement->recursion)
● (if->while)
● (expression->function)
● (variable->assignment) replacing the value of a variable.
http://agilekatas.co.uk/katas/RomanNumerals-Kata

12. Share your experience!

13. The Kata
Transformation priorities:
● ({}–>nil) no code at all -> code that returns nil
● (nil->constant)
● (constant->constant+) simple to a more complex constant
● (constant->scalar) replacing a constant with a variable
● (statement->statements) adding more unconditional
statements
● (unconditional->if) splitting the execution path
● (scalar->array)
● (array->container)
● (statement->recursion)
● (if->while)
● (expression->function)
● (variable->assignment) replacing the value of a variable.
http://agilekatas.co.uk/katas/RomanNumerals-Kata

14. Share your experience!

15. Benefits?

16. Benefits
Easier and more effective TDD
● Complexity based guideline for choosing
next test & implementation
● Reduces getting stuck with too big steps
● Less tests that are already green
● Less tests left out

17. Issues?

18. Issues
● Are there other transformations? (almost certainly)
● Are these the right transformations? (probably not)
● Are there better names for the transformations? (almost
certainly)
● Is there really a priority? (I think so, but it might be more
complicated than a simple ordinal sequence)
● If so, what is the principle behind that priority? (some
notion of “complexity”)
● Can it be quantified? (I have no idea)
● Is the priority order presented in this blog correct? (not
likely)
● The transformations as described are informal at best.
Can they be formalized? (That’s the holy grail!)
Raised by Uncle Bob

19. Retrospective

20. Special Thanks
to Ivan Kusalic
@ikusalic
for your inspiration

21. Images
THOR
https://commons.wikimedia.org/wiki/File:Parkour_leap_of_faith.j
pg?uselang=de
Seattle Municipal Archives
https://commons.wikimedia.org/wiki/File:Kids_at_Kubota_Garde
n_2003.jpg

22. Lizenz
Creative Commons Attribution-ShareAlike 3.0
https://creativecommons.org/licenses/by-sa/3.0/de/