ordinalize based on active_support's

ordinalize.rb

require 'minitest/autorun'
require 'minitest/pride'

class Integer
  def ordinalize
    suffix = if (abs % 100).between? 11, 13
      'th'
    else
      case abs % 10
      when 1; 'st'
      when 2; 'nd'
      when 3; 'rd'
      else    'th'
      end
    end

    "#{self}#{suffix}"
  end

  alias_method :to_ord, :ordinalize
end

class TestOrdinalization < MiniTest::Unit::TestCase
  def test_single_digit_numbers
    assert_equal "-1st", -1.to_ord
    assert_equal "1st", 1.to_ord
    assert_equal "2nd", 2.to_ord
    assert_equal "3rd", 3.to_ord
    assert_equal "4th", 4.to_ord
    assert_equal "5th", 5.to_ord
  end
  
  def test_oddball_cases
    assert_equal "11th", 11.to_ord
    assert_equal "12th", 12.to_ord
    assert_equal "13th", 13.to_ord
    assert_equal "-13th", -13.to_ord
  end
  
  def test_double_and_triple_digit_numbers
    assert_equal "21st", 21.to_ord
    assert_equal "55th", 55.to_ord
    assert_equal "102nd", 102.to_ord
    assert_equal "113th", 113.to_ord
    assert_equal "999th", 999.to_ord
    assert_equal "-999th", -999.to_ord
  end
end