The Transformation

Priority Premise

Softwerkskammer Meetup Munich

11.02.2016

David Völkel

Agenda

● Pizza

● Theory

● Kata

● Another Beer

Problem

Stuck with TDD

Too much to implement in one test

Image by Thor

Solution

Take Baby Steps

Image by Seattle Municipal Archives

What to choose next?

Simple to Complex

● What is the most simple

implementation?

● Uncle Bob‘s guideline: the

„Transformation Priority Premise“

Test Driven Development

red

refactor

green

Types of Code

Testcode

red

refactor

green

„Transformation“

= Implementation

Refactoring

Design

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.

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

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

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

Share your experience!

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

Share your experience!

Benefits?

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

Issues?

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

Retrospective

Special Thanks

to Ivan Kusalic

@ikusalic

for your inspiration

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

Lizenz

Creative Commons Attribution-ShareAlike 3.0

https://creativecommons.org/licenses/by-sa/3.0/de/