Test Driven Development solutions to same problem

!WARNING - THIS POST IS WRITTEN FOR SOFTWARE FOLKS!

I discovered Test Driven Development / TDD in about 2005/6 thanks to Gunjan Doshi's TDD Rhythm and 1-2 old articles on JavaWorld.

Years later I read Kent Beck's book Test Driven Development (The Addison-Wesley Signature Series) (or US) and was glad I had not missed anything fundamental from my non-standard "foundations" on the subject. These days there is a fairly good intro on Test Driven Development wikipedia entry. This post is aimed at software craftsmen and journeymen and perhaps even masters - to inspire a bit of thought along the following dimensions that impact the solutions that evolve:
- the understanding of the functional requirement
- the understanding of the non-functional requirement
- approaching the solution in primarily an iterative approach (managing complexity, perhaps)
- approaching the solution in primarily an incremental approach (managing complication, perhaps)
- the understanding of the required test strategy to ensure required quality level is achieved

Dimensions that, in TDD, result in the tests selected AND the order in which to approach the tests, which result in the emerging of different solutions.

I've spent a great deal of time leading/mentoring/coaching Test Driven Development (TDD) sessions, working with teams and individuals on a particular problem which they had no experience in beforehand. These sessions were the correct environment for us both to learn TDD, or for them to learn TDD, or even as part of a recruitment selection process where the team was practising TDD and we had to ensure candidates could practice TDD as we did.

I selected a problem that was documented on wikipedia on the page describing Numerology. I like discovering interesting coding problems on wikipedia as the descriptions there are [theoretically] internationally acceptable and understandable - which helps enormously to "level the playing field" for English first language speakers as well as non-English first language speakers.

The specific problem I wanted to pair up on is described very well under "Methods" in terse language (another "pro" as time is always pressured, and I wanted a problem understood, solved and discussed in 30-45 minutes).
In essence for this challenge, I wanted solutions to be developed that would convert a word, a phrase, and ultimately a person's full name, into a number, using simple rules that had to be analysed on the wikipedia page and extracted, without my help, to establish the even playing-field going into the solution development phase and discussion phase thereafer.

The first part of the rules were simply how to encode letters to numbers according to Numerology:

1 = a, j, s;
2 = b, k, t;
3 = c, l, u;
4 = d, m, v;
5 = e, n, w;
6 = f, o, x;
7 = g, p, y;
8 = h, q, z;
9 = i, r

The second part of the rules would usually give the candidate 2 strategies depending on how detail-oriented the person was.

For those who rushed through understanding the requirements, the rules were simply summing individual numbers repeatedly until the total < 10, eg using the wikipedia examples:

3489 ? 3 + 4 + 8 + 9 = 24        ? 2 + 4 = 6
Hello ? 8 + 5 + 3 + 3 + 6 = 25  ? 2 + 5 = 7

For those who paid a bit more attention, the rules were simply:

  value modulo 9, if 0, then 9

It is *always* interesting to see who picks up the shorter modulo 9 strategy, and who does not. (feeding into a lightweight Belbin assessment - see my Coaching with Belbin)

The various solutions below highlight [clearly] how the right problem tackled in the right way creates a much more readable, maintainable, extensible and flexible solution using TDD. Although even the less TDD-correct approach still produces an acceptable result. For me though, the best solution was actually produced largely without using TDD. Can you spot it?

/***************************************/
// TESTS
/***************************************/

I have removed name identifications and some "interesting" tests from the typical TestClasses that were all similar to either:

// Simple

import Calculator;
import org.junit.Test;
import static org.junit.Assert.*;
public class CalculatorTest {
    Calculator calculator = new Calculator();
    /*

     * Test Cases:     *    

     * 3,489 => 3 + 4 + 8 + 9 = 24 => 2 + 4 = 6     *          

     * Hello => 8 + 5 + 3 + 3 + 6 = 25 => 2 + 5 = 7  *

     */
    @Test public void testCalculateImportantChars() {        assertEquals(2, calculator.convertCharToNumeric('k'));        assertEquals(1, calculator.convertCharToNumeric('a'));        assertEquals(9, calculator.convertCharToNumeric('r'));        assertEquals(5, calculator.convertCharToNumeric('n'));        assertEquals(8, calculator.convertCharToNumeric('h'));        assertEquals(5, calculator.convertCharToNumeric('e'));        assertEquals(3, calculator.convertCharToNumeric('l'));        assertEquals(6, calculator.convertCharToNumeric('o'));        assertEquals(9, calculator.convertCharToNumeric('i'));        assertEquals(8, calculator.convertCharToNumeric('z'));    }

   @Test public void testCalculateHello() {        assertEquals(7, calculator.calculate("Hello"));    }
}

OR:

// More along Kent Beck's final example approach

import Calculator;
import org.junit.Test;
import static org.junit.Assert.*;

public class CalculatorTest {

   Calculator calculator = new Calculator();

   /*
    * A = 1
    * B = 2
    * C = 3
    * a = 1
    * b = 2
    * j = 1;
    * k = 2
    * i = 9;
    * 0 = 0
    * 1 = 1
    * 11 =  2
    *
    * AA = 2
    * AB = 3
    *
    * 1B2a =6
    */

   @Test
   public void testCalculate1() {

       String[] inputs = {"A", "a", "B", "b", "C", "k", "j", "i", "AA", "AB", "ABc", "0", "1", "11", ",", " ", "1B2a", "-1", "hello", "3,489"};
       int[] outputs = {1,1,2,2,3,2,1,9, 2, 3, 6, 0, 1, 2, 0, 0, 6, 1, 7, 6};

       for(int testcase=0; testcase < inputs.length; testcase++) {
           assertEquals(outputs[testcase], calculator.iWantToBelieve(inputs[testcase]));
       }

       assertEquals(-1, calculator.iWantToBelieve(null));
   }

}

/***************************************/
// SOLUTIONS, all checks and Exceptions removed for brevity
/***************************************/



/* Common Solution 1 */


public class Calculator {

   public int iWantToBelieve(String string) {
       if(null==string) {
           return(-1);
       }
       int result = 0;
       for(int pos = 0; pos < string.length(); pos++) {
           int valueToAdd;
           char currentChar = string.charAt(pos);
           if(Character.isDigit(currentChar)) {
               valueToAdd = Integer.valueOf(String.valueOf(currentChar));
           }
           else if(Character.isLetter(currentChar)){
                int tmpValue = Character.toUpperCase(currentChar) - 64;
               int valueOfCharacter = tmpValue % 9;
               valueToAdd = valueOfCharacter == 0 ? 9 : valueOfCharacter;
           }
           else {
               valueToAdd = 0;
           }
           result+=valueToAdd;
       }

       if(result>9) {
           result = iWantToBelieve(String.valueOf(result));
       }
       return(result);

   }

}


/* Common Solution 2 */


import java.util.HashMap;
import java.util.Map;

public class Calculator
{
 private static Map numericCodes = new HashMap();
  
  static 
  {
   numericCodes = initialiseNumerologyMap();
 }

 public Calculator(){
 }
  
 public int calculate(String word) {
   char[] chars = word.toLowerCase().toCharArray();
   int[] digits = new int[chars.length];
    
   for (int i = 0; i < chars.length; i++)
   {
       char characterValue = chars[i];
       Integer numeric = numericCodes.get(characterValue);
       if (numeric == null)
       {
         digits[i] = 0;
       } else {
         digits[i] = numeric;
       }
   }
   int sum = 0;
   for (int i = 0; i < digits.length; i++)
   {
     sum += digits[i];
   }
   if (sum > 9)
     return calculate(""+sum);
    
   return sum;
 }

 /* 
  * 1= a, j, s; 2= b, k, t; 3= c, l, u; 4= d, m, v; 5= e, n, w;
  * 6= f, o, x; 7= g, p, y; 8= h, q, z; 9= i, r  
  */
 private static Map initialiseNumerologyMap()
 {
   // a to z mappings
   for (int i=97; i<123; i++) {
     int alphabetValue = i%96;
     int modulatedValue = alphabetValue%9;
     if (modulatedValue == 0) {
       modulatedValue = 9;
     }
     numericCodes.put((char)i, modulatedValue);
   }
   // 0 to 9 mappings
   int j=0;
   for (int i=48; i<57; i++) {
     numericCodes.put((char)i, j);
     j++;
   }
   return numericCodes;
 }

}

/* Common Solution 3 */

public class Calculator {

   public int calculate(int n) {
       if (n == 0) {
           return 0;
       }

       int result = n % 9;
       if (result == 0){
           return 9;
       }
       return result;
   }

   private String a2n = "abcdefghijklmnopqrstuvwxyz";

   public int convertCharacter(char ch) {
       return calculate(a2n.indexOf(Character.toLowerCase(ch))+1);
   }

   public int convertWord(String word) {
       int sum = 0;
       for(char c : word.toCharArray()) {
           sum += convertCharacter(c);
       }

       return calculate(sum);
   }

}

/* Common Solution 4 */

public class Calculator {

   public int convertCharToNumeric(char c) {
       int intValue = (int)c;
       if ((intValue >95) && (intValue < 129)) {
           int numericFate = (intValue - 96) % 9;
           return convertForNumerology(numericFate);
       } else {
           return 0;
       }
   }

   private int convertForNumerology(int yourFate) {
       if (yourFate == 0) {
           return 9;
       }
       return yourFate;
   }

   public int calculate(String word) {
       int total = 0;
       for (char c : word.toLowerCase().toCharArray()) {
           total += convertCharToNumeric(c);
       }
       return convertForNumerology(total%9);
   }

}

/* Common Solution 5 */

public class Calculator {

   public int calculate(int n) {
       int result = n % 9;
       if (result == 0) {
           result = 9;
       }
       return result;
   }

   public int convert(String word) {
       String workingWord = word.trim().toLowerCase();

       int total = 0;
       for (char ch : workingWord.toCharArray()) {
           int intValue = (int)ch;
           if ((intValue > 96) && (intValue < 123)) {
               total += (intValue % 96);
           }
       }

       if (total > 0) {
           return calculate(total);
       }

       return 0;
   }

}


/* UnCommon Solution 6 */

public class Calculator {

   public int calculate(long n) {
       if(n%9==0)
           return 9;
       return (int)(n % 9);
   }

   public long convertStringToNumber(String string) {
       String tmpString = string;
       tmpString = tmpString.toLowerCase().replaceAll("[^abcdefghijklmnopqrstuvwxyz]", "");
       tmpString = tmpString.replaceAll("[a,j,s]", "1");
       tmpString = tmpString.replaceAll("[b,k,t]", "2");
       tmpString = tmpString.replaceAll("[c,l,u]", "3");
       tmpString = tmpString.replaceAll("[d,m,v]", "4");
       tmpString = tmpString.replaceAll("[e,n,w]", "5");
       tmpString = tmpString.replaceAll("[f,o,x]", "6");
       tmpString = tmpString.replaceAll("[g,p,y]", "7");
       tmpString = tmpString.replaceAll("[h,q,z]", "8");
       tmpString = tmpString.replaceAll("[i,r]", "9");
        return Long.parseLong(tmpString);
   }
  
}

/**************************/

It seems to me that TDD represents some interesting mental/psychological challenges for people who try:

• For software newbies, it is almost effortless, but they struggle to see the value in what they're creating as their solution emerges - I think due to a lack of experience looking at mountains of badly written and poorly designed legacy systems
• For software oldies, it is darn painful, and they struggle to see the value in the extra steps they're taking, constantly battling the urge to do more error checking and handling, to make the solution more complicated, and generally reach a point of suspended disbelief needing to see more examples and try it again in their work environments
• For some, and it is so far impossible for me to recognise them, they reach almost immediate "ah ha!" realisations of the power of TDD. They're flexible and open enough to suspend their not-as-entrenched over-thinking thought processes that the "oldies" display yet they have experience of maintaining some old production systems and dealing with some of their more novice mistakes that have come back to haunt them again, and sometimes again and again.
• Keith Braithwaite   and I once discussed that people applying TDD properly ("coincidentally" those who love doing so) experience  Csikszentmihalyi's "Flow"  - and hence even more benefits for those who successfully embrace, as well as the organisations that setup them up to succeed/embrace.

I look forward to hearing other points of view on the above 6 solutions for the "same problem" over the next few years.