introduction into tdd mantra

8/6/2019 Introduction Into TDD Mantra

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TestTest--Driven DevelopmentDriven DevelopmentAn introduction into the TDD MantraAn introduction into the TDD Mantra

Dennis van der SteltDennis van der Stelt

LogicaCMGLogicaCMG

Dennis van der SteltDennis van der Stelt

LogicaCMGLogicaCMG


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AgendaAgenda

1.1. A Quick IntroductionA Quick Introduction2.2. TestTest--Driven Development MantraDriven Development Mantra

3.3. RefactoringRefactoring

4.4. Benefits of TestBenefits of Test--Driven DevelopmentDriven Development5.5. DemoDemo

6.6. Key rules of TestKey rules of Test--Driven DevelopmentDriven Development

7.7. Mocking/StubbingMocking/Stubbing

8.8. Legacy CodeLegacy Code


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A Quick IntroductionA Quick Introduction

Unit testingUnit testing

Automated testingAutomated testing

Facilitates changeFacilitates change

Simplifies integrationSimplifies integration

System level documentationSystem level documentation

Seperates interface from implementationSeperates interface from implementation


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TDD MantraTDD Mantra

Write the testWrite the test

Write the codeWrite the code

RefactorRefactor

RepeatRepeat

REDRED

REDRED GREENGREEN

GREENGREEN REFACTORREFACTOR

REFACTORREFACTOR

IM TESTIM TEST--DRIVENDRIVEN

IM TESTIM TEST--DRIVENDRIVEN


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TDD MantraTDD Mantra

Where to begin?Where to begin?

Work from specification (or notes, orWork from specification (or notes, ornapkin)napkin)

Create a list of testsCreate a list of testsPick the simplest one.Pick the simplest one.

Make test, make code.Make test, make code.

RefactorRefactor

Find a bug? Create a test that wouldveFind a bug? Create a test that wouldve

caught it!caught it!


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TestTest--Driven DevelopmentDriven Development

...its about simple design that...its about simple design that

Runs all testsRuns all tests

Reveals all the intentionReveals all the intentionHas no duplicationHas no duplication

Has fewest number of classes andHas fewest number of classes and

methodsmethodsKent Beck, Extreme Programming Explained, 1999


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TestTest--Driven DevelopmentDriven Development

The act of writing a unit test is more an act of design then of verificationThe act of writing a unit test is more an act of design then of verification

-- Robert C. MartinRobert C. Martin

TestTest--driven development seeks specification, not validation, letting youdriven development seeks specification, not validation, letting you

think through your design before you write your functional codethink through your design before you write your functional code-- Scott AmblerScott Ambler

TestTest--Driven Development is a powerful way to produce well designed codeDriven Development is a powerful way to produce well designed codewith fewer defectswith fewer defects

-- Martin FowlerMartin Fowler

Fewer defects, less debugging, more confidence, better design, and higherFewer defects, less debugging, more confidence, better design, and higherproductivity in my programming practiceproductivity in my programming practice

-- Kent BeckKent Beck


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RefactoringRefactoring

Restructuring of softwareRestructuring of software

by applying a series of internalby applying a series of internalchanges that do not affect itschanges that do not affect its

observable behaviorobservable behavior

Martin Fowler, Refactoring, 2000


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Benefits of TDD (3/3)Benefits of TDD (3/3)

Cost of ChangeCost of Change

WaterfallTest-Driven Development embraces change!


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Cons of TDDCons of TDD

Needs practice, but youll learn to love it!Needs practice, but youll learn to love it!

Needs disciplineNeeds discipline

Need to know OODPNeed to know OODP

Scares away managersScares away managers


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Bowling gameBowling gameFirst a quick design sessionFirst a quick design session


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A quick design sessionA quick design session

Lets go ahead and design our bowling game.Lets go ahead and design our bowling game.

We clearly need the Gameclass.

A game has ten frames.A frame has 1 or 2 roles.

The tenth frame has two or three roles.It is different from all the other frames.

The score function must iteratethrough all the frames, andcalculate all their scores.

next framenext frame The score for spare or strikedepends on the frames succesor

1010 1..21..2

11


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Bowling gameBowling gameFinally some code!!!Finally some code!!!


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Key rules to TDDKey rules to TDD

A test is no unit test ifA test is no unit test if

it talks to a databaseit talks to a database

it communicates across the networkit communicates across the network

it touches the file systemit touches the file system

it cant run at the same time as otherit cant run at the same time as otherteststests

you have to perform actions to run theyou have to perform actions to run thetests (ex. configuration change)tests (ex. configuration change)

Michael Feathers, 2003


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Mocking / StubbingMocking / Stubbing

A mock or stub stands in forA mock or stub stands in for

an object outside your unitan object outside your unit

an external object (database)an external object (database)

a complex object(s)a complex object(s)

a not yet developed objecta not yet developed object

Mocking & Stubbing are different things!Mocking & Stubbing are different things!


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public class BusinessClass{

DataClass _dataLayer;

public BusinessClass(){

_dataLayer = new DataClass();}

public void PerformSomeSortOfAction(DataSet dataSet){

_dataLayer.SaveSomething(dataSet);}

}

Dependency injectionDependency injection


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public interface IDataAccessGateway

{ void SaveSomething(DataSet dataSet);}


private IDataAccessGateway _gateway;

public BusinessClass(IDataAccessGateway gateway){

_gateway = gateway;}


_gateway.SaveSomething(dataSet);}

}



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public interface IDataAccessGateway{

void SaveSomething(DataSet dataSet);}


private IDataAccessGateway _gateway;

public BusinessClass(IDataAccessGateway gateway){

_gateway = gateway;}

public BusinessClass() : this(new GateWay()) {}


_gateway.SaveSomething(dataSet);}

}



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How about .NET 2.0 Generics?How about .NET 2.0 Generics?

LoggerLogger

Stock QuotesStock Quotes

Web AppWeb App

AuthenticatorAuthenticator

Error HandlerError Handler DatabaseDatabase

Example originally created by Jim Weirich in Ruby on his blog.Conversion to .NET originally by Brad Wilson and Peter Provost.


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.NET 2.0 Generics : The old way.NET 2.0 Generics : The old waypublic class WebApp{

public WebApp(){quotes = new StockQuotes();

authenticator = new Authenticator();database = new DataBase();logger = new Logger();errorHander = new ErrorHandler();

}

// Some more code here

}


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.NET 2.0 Generics : First the interface.NET 2.0 Generics : First the interfacepublic interface ILocater{TObject Get();

}


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.NET 2.0 Generics : Example setting it up.NET 2.0 Generics : Example setting it uppublic interface ILocater{TObject Get();

}

public class MyLocator : ILocator

{protected Dictionary dict =new Dictionary();

public MyLocator(){dict.Add(typeof(ILogger), new Logger());dict.Add(typeof(IErrorHandler), new ErrorHandler());dict.Add(typeof(IQuotes), new StockQuotes());dict.Add(typeof(IDataBase), new Database());

dict.Add(typeof(IAuthenticator), new Authenticator());}}


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.NET 2.0 Generics : Get & use the objects.NET 2.0 Generics : Get & use the objectspublic interface ILocater{TObject Get();

}

public class MyLocator : ILocator

{protected Dictionary dict =new Dictionary();

public MyLocator(){dict.Add(typeof(ILogger), new Logger());dict.Add(typeof(IErrorHandler), new ErrorHandler());dict.Add(typeof(IQuotes), new StockQuotes());dict.Add(typeof(IDataBase), new Database());

dict.Add(typeof(IAuthenticator), new Authenticator());}}

public class StockQuotes{public StockQuotes(ILocator locator){errorHandler = locator.Get();logger = locator.Get();

}}


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How about legacy code?How about legacy code?public interface IDataService { }

// Nowpublic class ProxyToNastyLegacyDataService : IDataService { }

// Later

public class CleanNewCodeDataService : IDataService { }public class StranglerApplication{

public StranglerApplication(IDataService dataService) { }}

The term StranglerApplication was introduced by Martin Fowler in 2004.Read more at martinfowler.com


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Legacy codeLegacy code

Why is legacy code bad?Why is legacy code bad?The previous developer isnt there to explain it.The previous developer isnt there to explain it.

It takes time to learn the code.It takes time to learn the code.

Its not easy to change the code.Its not easy to change the code.

You might break some part of the applicationYou might break some part of the applicationyou didnt even touch.you didnt even touch.

Wikipedia :Wikipedia : Legacy code is source code thatLegacy code is source code thatrelates to a norelates to a no--longer supported or manufacturedlonger supported or manufacturedoperating system or other computer system.operating system or other computer system.

What is legacy code?What is legacy code?


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WRI E UNI TESTS!

Conclusion:

and do it the right way using Test-Driven Development.


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Web SitesWeb Siteshttp://www.agilealliance.org/http://www.agilealliance.org/http://xp.c2.com/ExtremeProgrammingRoadmap.htmlhttp://xp.c2.com/ExtremeProgrammingRoadmap.html

http://www.xprogramming.com/http://www.xprogramming.com/http://www.testdriven.com/http://www.testdriven.com/

BlogsBlogs

http://butunclebob.com/http://butunclebob.com/http://martinfowler.com/bliki/http://martinfowler.com/bliki/http://codebetter.com/http://codebetter.com/http://steve.emxsoftware.com/http://steve.emxsoftware.com/

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