Chapter 21

1. Chapter 21 Test Driven development

2. TDD • Write the test first • Show that test fails • Write code to pass the test • Run whole suite of tests! • This is unit testing

3. Why? • Testing gets done! • Programmer satisfaction • Clarification of interface and behavior • Provable repeatable verification • Confidence to change things

4. Warning • NO such thing as a complete and perfect test (No free lunch!)

5. jUnit • Many ide’s support jUnit testing • Requires adding library • Books shows jUnit 3 • jUnit version 4: • @org.junit.Test – method annotation • Assert methods: • assertEquals(“msg”,param1,param2)

6. Fig. 21.1

7. Refactoring Techniques • Extract method • Extract constant • Introduce Explaining variable • Replace constructor with factory

8. Fig. 21.2 public class Player { private Piece piece; private Board board; private Die[] dice; // … public void takeTurn() { // roll dice int rollTotal = 0; for (int i = 0; i < dice.length; i++) { dice[i].roll(); rollTotal += dice[i].getFaceValue(); } Square newLoc = board.getSquare(piece.getLocation(), rollTotal); piece.setLocation(newLoc); } } // end of class

9. Fig. 21.3 Extract Method public class Player { private Piece piece; private Board board; private Die[] dice; // … public void takeTurn() { // the refactored helper method int rollTotal = rollDice(); Square newLoc = board.getSquare(piece.getLocation(), rollTotal); piece.setLocation(newLoc); } private int rollDice() { int rollTotal = 0; for (int i = 0; i < dice.length; i++) { dice[i].roll(); rollTotal += dice[i].getFaceValue(); } return rollTotal; } } // end of class

10. Fig. 21.4 // good method name, but the logic of the body is not clear boolean isLeapYear( int year ) { return ( ( ( year % 400 ) == 0 ) || ( ( ( year % 4 ) == 0 ) && ( ( year % 100 ) != 0 ) ) ); }

11. Fig. 21.5 // that’s better! boolean isLeapYear( int year ) { boolean isFourthYear = ( ( year % 4 ) == 0 ); boolean isHundrethYear = ( ( year % 100 ) == 0); boolean is4HundrethYear = ( ( year % 400 ) == 0); return ( is4HundrethYear || ( isFourthYear && ! isHundrethYear ) ); }

12. Fig. 21.6

13. Fig. 21.7

14. Summary • TDD requires some paractice, but it can be powerful • Refactoring is a good approach to clean up!