TDD Kata 04: Word Wrap

This is my weekly Kata post. Read the first one to learn what it is all about.

Last week: Prime Factors

First, I closely followed the steps in the PowerPoint slides, except that I wrote a plain function instead of a class with static method, since this is PHP, not Java:

namespace PrimeFactors;

function generate($n)
{
    $primes = [];
    for ($candidate = 2; $n > 1; $candidate++) {
        for (;$n % $candidate == 0; $n /= $candidate) {
            $primes[] = $candidate;
        }
    }
    return $primes;
}

The next time, I tried an object oriented approach (obviously, putting the function into a class does not make it object oriented) and also used yield to get rid of the temporary variable $primes.

class Number
{
    private $n;

    public function __construct(int $n)
    {
        $this->n = $n;
    }

    public function primeFactors() : array
    {
        return iterator_to_array($this->primeFactorsGenerator($this->n));
    }

    private function primeFactorsGenerator(int $n) : Generator
    {
        for ($candidate = 2; $n > 1; $candidate++) {
            for (; $n % $candidate == 0; $n /= $candidate) {
                yield $candidate;
            }
        }
    }
}

I used this Kata to finally try out Behat. These are the first scenarios in my feature file:

Feature: Generate
  In order to calculate prime factors
  As a user of the library
  I want to retrieve the prime factors for a given number

  Scenario: Calculate prime factors of two
    Given I want to find all the prime factors for "2"
    When I calculate the prime factors
    Then I should be informed that the prime factors are "2"

  Scenario: Calculate prime factors of three
    Given I want to find all the prime factors for "3"
    When I calculate the prime factors
    Then I should be informed that the prime factors are "3"

  Scenario: Calculate prime factors of four
    Given I want to find all the prime factors for "4"
    When I calculate the prime factors
    Then I should be informed that the prime factors are "2,2"

I found this Gherkins syntax quite verbose for such a low level test, and it’s probably not made for that anyway. I understand Behat as a framework to write specifications on a business level that can be translated into tests.

“Calculate prime factors” is not a typical end user requirement, but well, it was still a good one to get started with Behat. The PhpStorm integration is also decent. I am looking forward to do more with it.

Fourth Kata: Word Wrap

Word Wrap was described by Uncle Bob in the “Craftsman” series. Read it in story form here: http://thecleancoder.blogspot.de/2010/10/craftsman-62-dark-path.html

“Yeah, it’s a simple problem to understand, but it’s oddly difficult to solve. The basic premise is really simple. You write a class called Wrapper, that has a single static function named wrap that takes two arguments, a string, and a column number. The function returns the string, but with line breaks inserted at just the right places to make sure that no line is longer than the column number. You try to break lines at word boundaries.”