Essential Test-Driven Development

TL Half‐day Tutorial 6/4/2013 1:00 PM

"Essential Test-driven Development"

Presented by:

Rob Myers Agile Institute

Brought to you by:

340 Corporate Way, Suite 300, Orange Park, FL 32073 888‐268‐8770 ∙ 904‐278‐0524 ∙ [email protected] ∙ www.sqe.com

Rob Myers Agile Institute

Rob Myers is founder of the Agile Institute and a founding member of the Agile Cooperative. With twenty-seven years of professional experience on software development teams, Rob has consulted for leading companies in aerospace, government, medical, software, and financial sectors. He has been training and coaching organizations in Scrum and Extreme Programming (XP) management and development practices since 1999. Rob’s courses—including Essential Test-Driven Development and Essential Agile Principles and Practices—are a blend of enjoyable, interactive, hands-on labs plus practical dialog toward preserving sanity in the workplace. Rob performs short- and long-term coaching to encourage, solidify, and improve the team's agile practices.

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As you enter the room…

1. Take a 3x5 card or piece of paper, create two columns.

2. Write these skills in the first column: TDD, Refactoring,

OO, Java (or C#), Eclipse (or IDEA or VisualStudio)

3. For each skill, rate yourself from 0 (never heard of it) to

10 (invented it), and record in the second column.

4. Find someone (a) whom you don’t usually work with; and

(b) who has somewhat complementary skill levels (with (b) who has somewhat complementary skill levels (with

them, your average is 4 to 6). Write down this person’s

name, but only if both a and b are true.

5. Repeat step 4 until you have two names.

17 April 2013 © Agile Institute 2008-2013 1

…get comfortable.

1. Choose someone from

your list to work with.y

2. Gather your belongings

and select a workstation

for you and your new

lab partner.

3. Settle in at that

workstation.


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EssentialEssentialTest-Driven Development

Rob Myersfor


forAgile Development Practices

West04 June 2013

Unit testing i is soooo

DEPRESSING


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TDD is fun,and provides

much more than just unit-tests!just unit-tests!


“The results of the case studies indicate

that the pre-release defect density of the

four products decreased between 40%p

and 90% relative to similar projects that

did not use the TDD practice.

Subjectively, the teams experienced a

15 35% i i i i i l d l


15–35% increase in initial development

time after adopting TDD.”http://research.microsoft.com/en-us/projects/esm/nagappan_tdd.pdf, Nagappan et al,

© Springer Science + Business Media, LLC 2008

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TDD Demo


No Magic

import org.junit.*;

public class FooTests {@Testpublic void fooBarIsBaz() {

Foo foo = new Foo();Assert.assertEquals("Baz", foo.bar());

}


}

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Requirements & Conventions

import org.junit.*;

public class FooTests {@Testpublic void fooBarIsBaz() {

Foo foo = new Foo();Assert.assertEquals("Baz", foo.bar());

}


}

Expected Actual

BarFoo

Basic UML Class Diagrams

+ void AbstractMethod(object parameter)

Baz

- int privateVariable

+ int PublicMethod()


- void PrivateMethod()

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Global Currency Money-Market Account


Global


GlobalATM

Access

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Stories

• As Rob the US account holder, I want to be able to

withdraw USD from a US ATM, but select which currency

holdings to withdraw from.

• As Rob, traveling in Europe, I want to be able to withdraw

EUR from either my EUR holdings or my USD holdings. The

default should be the most beneficial to me at the time.

• Shortly after the end of each month, I want to receive a y ,

report of my holdings and balance. The total balance

should appear in the currency of my account address

(USD).


Primary Objects

Currency

Account

Holding


o d g

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More Detail

Currency

CurrencyConverter

Holding

valuecurrencycurrencyConverter

convert value to


u e cy o e teco e t a ue toanother currency

Start Simple

To DoWhen currencies are the same.When currencies are the same.When value is zero.


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Specification, and Interface

@Testpublic void givesSameValueWhenSameCurrencyRequested() {

CurrencyConverter converter = new CurrencyConverter();String sameCurrency = "USD";double sameValue = 100.0000;double converted = converter.convert(

sameValue, sameCurrency, sameCurrency);Assert.assertEquals(sameValue, converted, 0.00004);

}


Will not compile. Will not compile.

“Thank You, But…”

public class CurrencyConverter {public double convert(

double value, String from, String to) {throw new RuntimeException(

"D'oh! convert() not YET implemented!");}

}


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“…I Want to See it Fail Successfully”


double value, String from, String to) {return 0.0;

}}


Technique: “Fake It”


double value, String from, String to) {return 100.0;

}}


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a. Refactor Away the Duplication@Testpublic void givesSameValueWhenSameCurrencyRequested() {

CurrencyConverter converter = new CurrencyConverter();String sameCurrency = "USD";String sameCurrency USD ;double sameValue = 100.0000;double converted = converter.convert(

sameValue, sameCurrency, sameCurrency);Assert.assertEquals(sameValue, converted, 0.00004);

}


public double convert(double value, String from, String to) {return 100.0;

}

b. Triangulate


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We don’t add any behavior

without a failing test…


Rodin’s The Thinker, photo by CJ on Wikipedia

Technique: “Triangulation”

@Testpublic void givesZeroWhenValueIsZero() {

CurrencyConverter converter = new CurrencyConverter();double zero = 0.0000;double converted = converter.convert(

zero, "USD", "EUR");Assert.assertEquals(zero, converted, 0.00004);

}


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Still “Fake”?


double value, String from, String to) {return value;

}}


Maintain the Tests


CurrencyConverter converter = new CurrencyConverter();// ...

}


CurrencyConverter converter = new CurrencyConverter();// ...


}

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@Before Runs Before Each Testprivate CurrencyConverter converter;

@Beforepublic void initialize() {

converter = new CurrencyConverter();}


// ...}



// ...}

What is the Expected Answer?

@Testpublic void convertsDollarsToEuros() {

double converted = converter.convert(100.0000, "USD", "EUR");

Assert.assertEquals(???, converted, 0.00004);}


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Let’s Invent a Scenario…

@Testpublic void convertsDollarsToEuros() {

double converted = converter.convert(100.0000, "USD", "EUR");

Assert.assertEquals(50.0000, converted, 0.00004);}


…“Fake It”…

public double convert(double value, String from, String to) {if (to.equals(from))

return value;return value * 0.5000;

}


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…Refactor…

public double convert(double value, String from, String to) {if (to.Equals(from))

return value;return value * conversionRate(from, to);

}

private double conversionRate(String from, String to) {return 0.5000;

}


…And Make a Note of It

To DoWhen currencies are the same.When currencies are the same.When value is zero.Fix the hard-coded conversionRate


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Well, What is It???


Where does it come from?

Circumstantial Coupling?

CurrencyConverter


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Managing the Transaction

CurrencyConverterAccount

ConversionRates

Holding

Holding

Holding

Holding


o d g

Another Object Emerges

To Do

When currencies are the sameWhen currencies are the same.

When value is zero.

Fix hard-coded conversionRate().

Write ConversionRates.

Make a factory for ConversionRatesthat uses the FOREX.com Web Service.


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import org.junit.Assert;import org.junit.Test;

New Test Class

public class ConversionRatesTest {@Testpublic void storesAndRetrievesRates() {

ConversionRates rates = new ConversionRates();String from = "USD";String to = "EUR";double rate = 0.7424;rates.putRate(from, to, rate);Assert.assertEquals(rate, rates.getRate(from, to),

0.0004);}

}


Fail

public class ConversionRates {public void putRate(String from, String to, double rate) {}

public double getRate(String from, String to) {return 0;

}}


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Technique: “Obvious Implementation”import java.util.HashMap;import java.util.Map;

public class ConversionRates {public class ConversionRates {private Map<String, Double> rates

= new HashMap<String, Double>();

public void putRate(String from, String to, double rate) {rates.put(from + to, rate);

}


public double getRate(String from, String to) {return rates.get(from + to);

}}

Isolate Behaviorpublic class ConversionRates {

private Map<String, Double> rates= new HashMap<String, Double>();

public void putRate(String from, String to, double rate) {rates.put(key(from, to), rate);

}public double getRate(String from, String to) {

return rates.get(key(from, to));}


private String key(String from, String to) {return from + to;

}}

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Next?

To Do

When currencies are the sameWhen currencies are the same.

When value is zero.

Fix hard-coded conversionRate().

Write ConversionRates.

Make a factory for ConversionRatesthat uses the FOREX.com Web Service.


Fix @Before Method

public class CurrencyConverterTests {private CurrencyConverter converter;

@Beforepublic void initialize() {

ConversionRates rates = new ConversionRates();rates.putRate("USD", "EUR", 0.5000);converter = new CurrencyConverter(rates);

}


// ...

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Partially Refactored…

public class CurrencyConverter {private ConversionRates rates;public CurrencyConverter(ConversionRates rates) {

this.rates = rates;}

private double conversionRate(String from, String to) {return 0.5000;

}


// ...

Replace the Hard-Coded Value

public class CurrencyConverter {private ConversionRates rates;public CurrencyConverter(ConversionRates rates) {

this.rates = rates;}

private double conversionRate(String from, String to) {return rates.getRate(from, to);

}


// ...

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What Remains?

To DoWhen currencies are the same.When currencies are the same.When value is zero.Fix hard-coded conversionRate().Write ConversionRates.Make a factory for ConversionRatesMake a factory for ConversionRatesthat uses the FOREX.com Web Service.


What is the Missing Piece?

ConversionRates rates =

ConversionRates.byAccountAnd???(account, ???);


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Ask What If…?

To DoMake a byAccountAndDate() factory Make a byAccountAndDate() factory for ConversionRates that uses the FOREX.com Web Service.ConversionRates returns 1/rate if inverse rate found.ConversionRates throws when rate not found.


Testing Exceptional Behavior

@Test(expected=RateNotFoundException.class)public void throwsExceptionIfRateNotFoundII() {

ConversionRates rates = new ConversionRates();String from = "BAR";String to = "BAZ";rates.getRate(from, to);

}


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A New Exception

public class RateNotFoundException extends RuntimeException {}



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Back in ConversionRates

public double getRate(String from, String to) {if (!rates.containsKey(key(from, to)))

throw new RateNotFoundException();return rates.get(key(from, to));

}


1. Write one unit test.

2. Build or add to the object under test until everything compiles.

steps

3. Red: Watch the test fail!

4. Green: Make all the tests pass by changing the object under test.


5. Clean: Refactor mercilessly!

6. Repeat.

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Runs all the tests.Expresses every idea required.

Says everything once and only once.Has no superfluous parts.


Exercise A: Password-Strength Checker

In order to be an acceptable password, a string must:

Have a length greater than 7 characters.

Contain at least one alphabetic Co ta at east o e a p abet ccharacter.

Contain at least one digit.


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steps





6. Repeat.

Iteration 2

• Admins and regular users:

• Admin passwords must also...

• Be > 10 chars long

• Contain a special character

• People want to know all the reasons why their password has failed.

• Other stronger rules may apply later. ;-)

• HINT: What is varying most frequently?

Be sure to take a break when you need one!


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steps





6. Repeat.

1. _______________________________________

2. _______________________________________

3. _______________________________________

CLOSING


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[email protected]

http://PowersOfTwo.agileInstitute.com/


@agilecoach

Essential Test-Driven Development

Technology

Transcript of Essential Test-Driven Development