1. Test Driven development
Chapter 21
Test Driven development

2. Write code to pass the test Run whole suite of tests!
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. Programmer satisfaction Clarification of interface and behavior
Why?
Testing gets done!
Programmer satisfaction
Clarification of interface and behavior
Provable repeatable verification
Confidence to change things

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

5. 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. Four listed in the test: Extract method Extract constant
Refactoring
Four listed in the test:
Extract method
Extract constant
Introduce Explaining variable
Replacer 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. TDD requires some paractice, but it can be powerful
Summary
TDD requires some paractice, but it can be powerful
Refactoring is a good approach to clean up!