Test Driven Development and JUnit

Somenath Mukhopadhyay

Test Driven Development

vis-à-vis JUnit

by Somenath [email protected]


What does it mean?

• Principle: Clean Code that works

• Purpose: o Removes fear factors from programmerso Depicts clearly what the code is doingo Programmers don’t have to wait for the long

trails of bugs and fixing of those bugs


Three Steps in TDD

• RED – a failed test case

• GREEN – the test case just passes

• REFACTOR – change the code to meet good design principles


Example

• We need to create a Book class• The Book class will have Author’s name• It will have Price• It will have setter and getter functions to

access its attributes• It will have equal functionality to compare

two books• It will have functionality to calculate its

price in different currencies


Various steps of a TDD

• Quickly add a test

• Run the test case to see it fail

• Make a little change to see the test pass

• Refactor the code to suit the specific need


Quickly add a test

• Book book1• book1.setAuthor(“Som”)• book1.setPrice(10.11)• assertTrue(book1.getAuthor().equals(“So

m”))• assertTrue(book1.getPrice() == 10.11)


Run the Test

• Ii will obviously fail

• It is the “RED” stage in JUnit

• No Book class has been defined


Make a little change to see the test Pass

• Create a Class Book having two attributes

• public class Book {string iAuthor;double iPrice;Book();public void setAuthor(string aAuthor){iAuthor = aAuthor;}public void setPrice(double aPrice){iPrice = aPrice;}string getAuthor(){return iAuthor;}double getPrice(){return iPrice;}

• };


Run the Test again

• With the Book class in hand the test will pass the first hurdle

• It is a GREEN state in JUnit


Refactor the Code

• We will create two constructors:

Book() {this.Author = NULL, this.Price = 0.0)

Book (string Author, double Price)

• We will make the attributes private


Refactoring contd…run the test again…

• Book book2(“reema”, 20.33)

• Book book3(“som”, 10.11)

• assertFalse(book1.equals(book2))

• assertTrue(book1.equals(book3))


The test will fail again

• There is no equals functionality defined• Lets Refactor it again and define it right away• public boolean equals(Object object) {• if (object instanceof Book) {• Book book = (Book) object;• return (getAuthor().equals(book. getAuthor())• && getPrice() == book.getPrice());• }• return false;• }


Run the test again

• The test will pass now.

• It is the GREEN state


Refactor.. Refactor..

• What is left is the currency issue

• So we will add another private string parameter called currency in the book class


Refactor… Refactor…

• The constructor of the Book class will now take three parameters

• Book (string Author, double price, string currency)

• We need to construct the objects asBook book1(“Som”,12.12, “Yen”)Book book2(“Reema”, 13.13, “Rupees”)



• So we are left with only the convertibility of price between different currencies.

• We can add this function inside Book class• Hold on! Should this function be Book’s

responsibility.• We can have a modular design if we

create a new Currency class



• Public class Currency {• private String country;• Public Currency() {this.currency = “USA”}• Public Currency(string country)• Public void setCountry(string c)• Public string getCountry();• public void Convert (Currency to);• }


Finally

• So finally the Book class will look as follows• public class Book {• private string Author;• private double price;• private Currency currency;• Public Book (String Author, double price, Currency c)• public void setAuthor (string Author)• Public void setPrice (double Price)• Public void setCurrency(Currency c)• Public string getAuthor();• Public double getPrice();• Public Currency getCurrency(); • Public booloean equals (Object book) • }


Refactoring.. Final touch to the Equals function

• public boolean equals(Object object) {• if (object instanceof Book) {• Book book = (Book) object;• return (getAuthor().equals(book. getAuthor())• && getPrice() == book.getPrice() &&

getCurrency().equals (book.getCurrency());• }• return false;• }


Run the test again

• It will again fail• We didn’t define the equals function for the currency

class• The equals function of the currency class will look as

follows:• public bool equals(Object c)• {• If (c instanceof Currency)• {• return( getCurrency().getCountry().equals(c.getCurrency(

).getCountry())• }


The Refactoring is Over

• The test case will pass now

• It will be a “GREEN” state

• I will leave the Convert Function of the Currency class for you to implement


The JUnit Codeimport junit.framework.Test;import junit.framework.TestCase;import junit.framework.TestSuite; public class BookTest extends TestCase { private Book book1; public BookTest(String name) { super(name); }

protected void setUp() throws Exception { super.setUp(); book1 = new Book("Som", 10.11); book2 = new Book("Reema", 12.33); book3 = new Book("Som", 10.11); }

Contd.....


The JUnit Codeprotected void tearDown() throws Exception { super.tearDown(); book1 = null; book2 = null; book3 = null; } public void testEquals() { assertFalse(book2.equalsBook(book1)); assertTrue(book1.equalsBook(book1)); assertTrue(book1.equalsBook(book3)); } public void testGetPrice() { double price = book1.getPrice(); assertTrue(price == 10.11); }

Contd...


The JUnit Codepublic void testSetPrice() { book1.setPrice(15.15); double price = book1.getPrice(); assertTrue(price == 15.15); } public void testGetTitle() { String title = book2.getTitle(); boolean result = title.equals("Reema"); assertTrue(result == true); } public static Test suite(){ TestSuite suite = new TestSuite(); suite.addTest(new BookTest("testEquals")); suite.addTest(new BookTest("testGetTitle")); suite.addTest(new BookTest("testSetPrice")); return suite; }

Thank You

Test Driven Development and JUnit

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book book2reema

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