Introduction to Test Driven Development

Introduction to Test Driven Development

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  An Introduction to Test Driven Development Michael Denomy Nashua Scrum Club January 13, 2011 www.mdenomy.wordpress.com
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  Goals Basic understandingof TDD Benefits of TDD TDD in action TDD and Scrum Challenges to Implementing TDD Question and Answer
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  What Is TestDriven Development? Iterative, test-first approach to development Functionality and behavior The tests define the behavior we want API Developed from client's perspective Design Incremental, evolving with test definition Testing Well tested software with high code coverage
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  History of TDDKent Beck recognized as originator of TDD Extreme Programming in mid 90's Initially used custom test fixtures JUnit framework Developed by Beck and Erich Gamma in '97 Simplified writing and executing tests JUnit ported to several languages .NET, C++, Python, PHP Referred to as xUnit frameworks
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  Benefits of TDDCase Studies 2008 study of 4 Projects using TDD 1 Pre-release defects decreased 40-90% 15-35% increase in initial development time Keith Braithwaite 2 2008 study on cyclomatic complexity and automated tests Projects with automated testing had lower complexity Lower complexity -> easier to refactor
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  Benefits of TDDOne Man's Experience TDD for high-throughput DNA sequencer Complex, distributed system Software developed and tested before hardware Reduced integration times Low defects in product releases More trust among developers Took some practice to get it right Hardly ever use a debugger anymore I won't write production code without it
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  Red-Green-Refactor
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  TDD In ActionBanking User Stories Open Account As a customer, I want to open a bank account with an initial deposit >= 0 dollars. After opening the account, the account balance should be the amount of the initial deposit. Deposit Funds As a customer, I want make a deposit into a bank account. After the deposit, the account balance should be the previous balance plus the amount of the deposit. The deposit amount must be >= 0 dollars Let's write some code
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  TDD and TeamCollaboration Banking examples were pretty simple, but we ended up with... Executable specifications that describe the behavior of the system Short, simple tests that are easy to understand Enables collaboration with Product Owners to define and clarify behaviors Q/A to expose edge cases and failure modes Other developers to understand the behavior and design
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  TDD and CommunicationContinuous Integration XP practice that automates build and test Tests run on every check in Results can show progress or identify areas for concern Total tests, passing/failing tests Results must be visible to whole team Use caution in interpreting metrics
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  TDD and DesignTDD encourages good design practices SOLID S ingle Responsibility Principle O pen-Closed Principle L iskov Substitution Principle I nterface Segregation Principle D ependency Inversion Principle SOLID allows for modular, loosely coupled systems
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  TDD and DesignYAGNI Don't put in code you don't need yet DRY “ Merciless refactoring to avoid duplication” Separation of Concerns e.g. don't embed business logic in UI layer Continually ask “How will I test this?” These principles keep the code clean and easier to modify
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  TDD and DesignWhat Others Have To Say If TDD has never led you to an unexpected design, you've got more to learn @JoshuaKerievsky The act of writing a unit test is more an act of design than of verification. It is also more an act of documentation than of verification Bob Martin, “Uncle Bob” ...you're always thinking about design. Either you're deciding which test you're going to write next, which is an interface design process, or you're deciding how to refactor, which is a code design process. James Shore
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  Challenges To TDDTeams will struggle adopting TDD Requires strong design skills Writing “all that extra test code” How much were you writing before? Practice, practice, practice “ The basic steps of TDD are easy to learn, but the mindset takes a while to sink in. Until it does, TDD will likely seem clumsy, slow, and awkward. Give yourself two or three months of full-time TDD use to adjust.” - James Shore
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  Introducing a NewTeam to TDD Understand that teams new to TDD will struggle Start small Pick a small project to gain experience Develop internal experts Training options Coaching Pair programming Katas Focus on good design practices
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  Summary Enables betterteam communication Mechanism for team collaboration Tests become executable specifications Encourages good design practices Small classes, loosely coupled High test coverage Reduced defects, faster integration Will have significant learning curve Practice, practice, practice
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  Books on Agileand TDD Kent Beck Test-Driven Development By Example James Shore The Art of Agile Development http://jamesshore.com/Agile-Book/ Roy Osherove The Art of Unit Testing With Examples in .NET Michael Feathers Working Effectively With Legacy Code
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  Online Tutorials andKatas James Shore - “Let's Play TDD” http://jamesshore.com/Blog/Lets-Play Roy Osherove – String Calculator TDD Kata http://www.osherove.com/tdd-kata-1/ List of TDD Exercises http://sites.google.com/site/tddproblems/all-problems-1
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  Case Study ReferencesRealizing quality improvement through test driven development: Nagappan, Maximilien, Bhat and Williams http://research.microsoft.com/en-us/groups/ese/nagappan_tdd.pdf Keith Braithwaite – Quantifying the Effect of TDD http://www.keithbraithwaite.demon.co.uk/professional/presentations/2008/qcon/MeasureForMeasure.pdf George Dinwiddie – Studies of TDD http://biblio.gdinwiddie.com/biblio/StudiesOfTestDrivenDevelopment GoogleDoc Spreadheet on TDD References https://spreadsheets.google.com/ccc?key=0AuC-Rc25Sw9VdEw0WE5wNmtIQ1d2eFA3UEFBUENfa0E
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  An Introduction to Test Driven Development Michael Denomy Nashua Scrum Club January 13, 2011 www.mdenomy.wordpress.com