Ping Pong TDD

Ping pong is one of the most basic activities used when teaching Test Driven Development (TDD) . The rules are simple:

Work in pairs
Person A only writes tests (test code only)
Person B only tries to get the tests to pass (production code only)
Both persons refactor when appropriate

During the activity, it a good idea to ask participants to switch roles. Person B becomes the test writer, and Person A becomes the test taker (or the person who gets the tests to pass).

This Lab shows how TDD can be easy and fun by combining it with pair programming. As if you were playing table tennis, in ping pong TDD you create a test for your partner to pass, and then he creates one for you.

This exercise is to create a unit of code that converts Roman numbers into Arabic numerals. Were going to show how the development proceeds when we work in the smallest possible increments

Player 1:

@Test
public void testNumber1() {
    assertEquals(1,RomanConverter.Convert("I"));
}

Player 2:

public class RomanConverter {
        public static int Convert(String s) 
        {
            return 1;
        }
}

@Test
public void testNumber2() {
    assertEquals(2,RomanConverter.Convert("II"));
}

Player 1:

public class RomanConverter {
    public static int Convert(String s) 
    {
        return s.length();
    }
}

@Test
public void testNumber5() {
    assertEquals(5,RomanConverter.Convert("V"));
}

Player 2:

public class RomanConverter {
    public static int Convert(String s) 
    {
        if (s.equals("V") {
            return 5;
        }
        else {
            return s.length();
        }
    }
}

@Test
public void testTwoDifferentNumbers() {
    assertEquals(6,RomanConverter.Convert("VI"));
}

Player 1:

public class RomanConverter {
    public static int Convert(String s) 
    {
        int sum = 0;
        for (int i = 0; i < s.length(); i++) {
            if (s.charAt(i) == 'I') {
                sum += 1;
            }
            else {
                sum+= 5;
            }
        }
    return sum;
}


@Test
public void testSmallchar() {
    assertEquals(6,RomanConverter.Convert("vi");
}

Continue until the final solution

Solution can use Regex to check for 4 characters in a row
Test case should make use of JUnit 5 features - CsvSource, ParameterizedTest and assertThrows
JUnit 5 guide can be found at http://junit.org/junit5/docs/current/user-guide/

Roman Numeral Rules

Symbol	Meaning	Decimal
I	One	1
V	Five	5
X	Ten	10
L	Fifty	50
C	One Hundred	100
D	Five Hundred	500
M	One Thousand	1000

Roman numerals follow this pattern:

Units	I	II	III	IV	V	VI	VII	VIII	IX
Tens	X	XX	XXX	XL	L	LX	LXX	LXXX	XC
Hundreds	C	CC	CCC	CD	D	DC	DCC	DCCC	CM
Thousands	M	MM	MMM	IV	V	VI	VII	VIII	IX

The Additive System

The system for writing Roman numerals is an additive system. This means to calculate the value of a Roman numeral, you simply to have to add up all the digits in the Roman numeral.

Roman Numerals are always written from Largest to Smallest – Left to Right.

Examples:

VIII = 5 + 1 + 1 + 1 = 8

XXXIII = 10 + 10 + 10 + 1 + 1 + 1 = 33

CLXXVIII = 100 + 50 + 10 + 10 + 5 + 1 + 1 + 1 = 178

MMX = 1,000 + 1,000 + 10 = 2,010 SUBTRACTIVE SYSTEMYou can write one smaller numeral to the left of a larger one to subtract from it! The table below has all the allowed subtractive combinations

Roman Numeral	Value	Equivalent
IV	4	IIII
IX	9	VIIII
XL	40	XXXX
XC	90	LXXXX
CD	400	CCCC
CM	900	DCCCC

Mpho-Kgosisejo/pingpongtddjunit5

Ping Pong TDD

Roman Numeral Rules

Examples: