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When coding using TDD, do you often run into a point when you have to “implement the whole thing”? The sequence of tests that we write significantly impacts where are code ends up! We’ll explore Uncle Bob’s Transformation Priority Premise, looking at the transformations that code goes through and how our tests can drive the code in different directions.
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Transformation Priority Premise: TDD Test Order Matters
Mike Clement@mdclement
[email protected]://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• [email protected]• http://blog.softwareontheside.com• http://agilecodegames.com• Utah Software Craftsmanship Group– http://utahsc.org– @utahsc
