- Test Driven Development (TDD) uses JUnit to write test cases before writing code to remove fear factors and clearly depict what the code is doing. - The three steps of TDD are Red (a failed test case), Green (the test passes), and Refactor (change code to meet design principles). - An example walks through writing tests for a Book class, making the tests fail, making them pass, and refactoring the code using TDD principles.

1. Test Driven Development vis-à-vis JUnit by Somenath Mukhopadhyay [email_address] Somenath Mukhopadhyay

2. What does it mean? Principle: Clean Code that works Purpose: Removes fear factors from programmers Depicts clearly what the code is doing Programmers don’t have to wait for the long trails of bugs and fixing of those bugs Somenath Mukhopadhyay

3. Three Steps in TDD RED – a failed test case GREEN – the test case just passes REFACTOR – change the code to meet good design principles Somenath Mukhopadhyay

4. 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 Somenath Mukhopadhyay

5. 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 Somenath Mukhopadhyay

6. Quickly add a test Book book1 book1.setAuthor(“Som”)‏ book1.setPrice(10.11)‏ assertTrue(book1.getAuthor().equals(“Som”))‏ assertTrue(book1.getPrice() == 10.11)‏ Somenath Mukhopadhyay

7. Run the Test Ii will obviously fail It is the “ RED ” stage in JUnit No Book class has been defined Somenath Mukhopadhyay

8. 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; } }; Somenath Mukhopadhyay

9. Run the Test again With the Book class in hand the test will pass the first hurdle It is a GREEN state in JUnit Somenath Mukhopadhyay

10. 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 Somenath Mukhopadhyay

11. Refactoring contd… run the test again… Book book2(“reema”, 20.33)‏ Book book3(“som”, 10.11)‏ assertFalse(book1.equals(book2))‏ assertTrue(book1.equals(book3))‏ Somenath Mukhopadhyay

12. 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 ; } Somenath Mukhopadhyay

13. Run the test again The test will pass now. It is the GREEN state Somenath Mukhopadhyay

14. Refactor.. Refactor.. What is left is the currency issue So we will add another private string parameter called currency in the book class Somenath Mukhopadhyay

15. 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 as Book book1(“Som”,12.12, “Yen”)‏ Book book2(“Reema”, 13.13, “Rupees”)‏ Somenath Mukhopadhyay

16. Refactor… Refactor… 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 Somenath Mukhopadhyay

17. Refactor… Refactor… 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); } Somenath Mukhopadhyay

18. 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) } Somenath Mukhopadhyay

19. 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 ; } Somenath Mukhopadhyay

20. 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())‏ } Somenath Mukhopadhyay

21. 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 Somenath Mukhopadhyay

22. The JUnit Code import 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..... Somenath Mukhopadhyay

23. The JUnit Code protected 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... Somenath Mukhopadhyay

24. The JUnit Code public 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; } Somenath Mukhopadhyay

25. Thank You