Test Driven Lasse Koskela Chapter 3: Refactoring in Small Steps Paul Ammann http://cs.gmu.edu/~pammann/

Overview Exploring a Potential Solution Changing Design in a Controlled Manner Taking the New Design Further The Most Powerful Designs Are Always the Result of a Continuous Process of Simplification and Refinement. 8/10/2019

Recalling the Problem Existing Design Replaced Variables Via Simple Matching For all variables v, replace ${v} with its value: result = result.replaceAll(regex, entry.getValue()) Failing test: @Before sets template value to “${one}, ${two}, ${three}” @Test public void variablesGetProcessedJustOnce() throws Exception { template.set(“one”, “${one}”); template.set(“two”, “${three}”); template.set(“three”, “${two}”); assertTemplateEvaluatesTo(“${one}, ${three}”, ${two}); } Tweaking the Current Design Won’t Make This Test Pass. 8/10/2019

Exploring A Potential Solution Exploring a “Segment” Solution for Templates Prototyping with Spikes A Spike is A Detour to Learn In Template Example, Learning is About regex Learning by Writing Tests Need to Figure Out An API? Write Some Test Code That Uses The API RegexlearningTest Example Spike for Learning an API Note Koskela’s Misunderstanding of the Role of Parentheses Simple Here: We’re Finding Variables in a Template Compiling Regex Patterns, Matching Expressions Get Smarter On The Side, Then Apply 8/10/2019

Changing Design in Controlled Manner Creating an Alternative Implementation Starting With the Low Hanging Fruit TDD Development of a Template Parser Removing Duplication From Tests Refactoring Is Always Important Applying Learning From the Spike Final Code Version (note Segment class, originally String) private void append(String segment, StringBuilder result) { if (isVariable(segment) { evaluateVariable(segment, result); } // dispatching  else { result.append(segment);} } Koskela Refactors Substantially TemplateParse.java Now We Can Parse; Next Step Is To Use Parser 8/10/2019

Changing Design in a Controlled Manner - Continued Switching Over Safely Adopting the New Implementation Recoding the evaluate() method Cleaning Up By Extracting Methods Pull Out The Old Stuff That ‘s No Longer Relevant Result is new Template Class Template.java No New Functionality, But Definitely Refactored 8/10/2019

Taking the New Design Further Keeping Things Compatible Building on Existing Functionality Note equals(), hashCode() treatment in Segment classes Any Worries About This? Segment, PlainText , Variable Refactoring Logic into Objects Tell, Don’t Ask! Motivation for Segment class Making the Switchover Getting Caught By the Safety Net Adding Exceptional Behavior! Deleting Dead Code and Further Clean Up Test Set Makes Requirements Concrete 8/10/2019