Transformation Priority Premise: TDD Test Order Matters

Transformation Priority Premise: TDD Test Order Matters

Mike Clement@mdclement

mike@softwareontheside.comhttp://blog.softwareontheside.com

http://agilecodegames.com

XP Simple Design

• Passes all tests• Clear, expressive, consistent• No duplication•Minimal

TDD Review

TDD

• Red• Green• Refactor

Ways to get Green

• Fake it• Obvious

implementation• Triangulation

Example Transformations

• ({}–>nil) no code at all->code that employs nil• (nil->constant)• (variable->assignment) replacing the value of

a variable.• (statement->statements) adding more

unconditional statements.

Uncle Bob’s Three Laws of TDD

• You are not allowed to write any production code unless it is to make a failing unit test pass.

• You are not allowed to write any more of a unit test than is sufficient to fail; and compilation failures are failures.

• You are not allowed to write any more production code than is sufficient to pass the one failing unit test.

Rule of Perpetual

Inconsequence

Proposed Transformations• ({}–>nil) no code at all->code that employs nil• (nil->constant)• (constant->constant+) a simple constant to a more complex constant• (constant->scalar) replacing a constant with a variable or an argument• (statement->statements) adding more unconditional statements.• (unconditional->if) splitting the execution path• (scalar->array)• (array->container)• (statement->recursion)• (if->while)• (expression->function) replacing an expression with a function or

algorithm• (variable->assignment) replacing the value of a variable.

WORD WRAPA Fork in the Road

Problem definition

• function named Wrap that takes two arguments, a string, and a column number

• The function returns the string, but with line breaks ('\n') inserted at just the right places to make sure that no line is longer than the column number.

• Try to break lines at word boundaries.

LET’S CODE!

?

"I can't seem to get this test to pass without writing a lot

of untested code."

They are the wrong tests, because you could not figure

out how to pass them.

"[W]hen faced with a problem you do not

understand, do any part of it you do understand, then

look at it again."

BACK UP!

The Premise Applied

• Prefer higher priority transformations.• Choose tests that can be passed with higher

priority transformations.• When a low priority transformation seems

required, backtrack to see if there is a simpler test to pass.

WHAT ABOUT SOLUTION QUALITY?Sorting Algorithms

The Premise Applied

• Prefer higher priority transformations.• Choose tests that can be passed with higher

priority transformations.• When a low priority transformation seems

required, backtrack to see if there is a simpler test to pass.

Proposed Prioritized Transformations

• ({}–>nil) no code at all->code that employs nil• (nil->constant)• (constant->constant+) a simple constant to a more complex constant• (constant->scalar) replacing a constant with a variable or an argument• (statement->statements) adding more unconditional statements.• (unconditional->if) splitting the execution path• (scalar->array)• (array->container)• (statement->recursion)• (if->while)• (expression->function) replacing an expression with a function or

algorithm• (variable->assignment) replacing the value of a variable.

ABSOLUTE PRIORITY PREMISE“Cousin” Micah

Action Items!

• Read the original post http://cleancoder.posterous.com/the-transformation-priority-premise

• Sorting: http://cleancoder.posterous.com/transformation-priority-and-sorting

• Fibonacci: http://cleancoder.posterous.com/fib-the-transformation-priority-premise

• Flash Card: http://cleancoder.posterous.com/flash-tpp• Uncle Bob on TPP: https://vimeo.com/60561303• “Cousin” Micah on APP: https://vimeo.com/57851350 and

https://vimeo.com/59265614• Experiment!

Software Craftsmanship!

• Participate in a local Software Craftsmanship group wherever home is for you.

My Contact Info

• @mdclement• mike@softwareontheside.com• http://blog.softwareontheside.com• http://agilecodegames.com• Utah Software Craftsmanship Group– http://utahsc.org– @utahsc