gilded_rose.rb

class GildedRose < Struct.new(:name, :days_remaining, :quality)

  def tick
    return if name == 'Sulfuras, Hand of Ragnaros'

    self.days_remaining -= 1

    case name
    when 'Aged Brie' then
      increase_quality
      increase_quality if days_remaining < 0
    when 'Backstage passes to a TAFKAL80ETC concert'
      increase_quality
      increase_quality if days_remaining < 5
      increase_quality if days_remaining < 10
      decrease_quality(quality) if days_remaining < 0
    when 'Conjured Mana Cake'
      decrease_quality(2)
      decrease_quality(2) if days_remaining <= 0
    else
      decrease_quality
      decrease_quality if days_remaining < 0
    end
  end

  protected

  def increase_quality(quantity = 1)
    self.quality += quantity if quality < 50
  end

  def decrease_quality(quantity = 1)
    self.quality -= quantity if quality > 0
  end
end

gilded_rose_test.rb

require "minitest/autorun"
require "minitest/pride"

require_relative './gilded_rose'


class GildedRoseTest < MiniTest::Unit::TestCase

  def update_quality_for_item_with(sell_in,
                                   quality,
                                   name             = 'normal item',
                                   sell_in_decrease = 1)

    item = GildedRose.new(name, sell_in, quality)
    item.tick
    assert_equal item.days_remaining, sell_in - sell_in_decrease
    item
  end

  def test_normal_item_before_sell_date
    item = update_quality_for_item_with(5, 10, 'normal')
    assert_equal 9, item.quality
  end

  def test_normal_item_on_sell_date
    item = update_quality_for_item_with(0, 10, 'normal')
    assert_equal 8, item.quality
  end

  def test_normal_item_after_sell_date
    item = update_quality_for_item_with(-10, 10, 'normal')
    assert_equal 8, item.quality
  end

  def test_normal_item_of_zero_quality
    item = update_quality_for_item_with(5, 0, 'normal')
    assert_equal 0, item.quality
  end

  def test_brie_before_sell_date
    item = update_quality_for_item_with(5, 10, 'Aged Brie')
    assert_equal 11, item.quality
  end

  def test_brie_before_sell_date_with_max_quality
    item = update_quality_for_item_with(5, 50, 'Aged Brie')
    assert_equal 50, item.quality
  end

  def test_brie_on_sell_date
    item = update_quality_for_item_with(0, 10, 'Aged Brie')
    assert_equal 12, item.quality
  end

  def test_brie_on_sell_date_near_max_quality
    item = update_quality_for_item_with(5, 49, 'Aged Brie')
    assert_equal 50, item.quality
  end

  def test_brie_on_sell_date_with_max_quality
    item = update_quality_for_item_with(5, 50, 'Aged Brie')
    assert_equal 50, item.quality
  end

  def test_brie_after_sell_date
    item = update_quality_for_item_with(-10, 10, 'Aged Brie')
    assert_equal 12, item.quality
  end

  def test_brie_after_sell_date_with_max_quality
    item = update_quality_for_item_with(-10, 50, 'Aged Brie')
    assert_equal 50, item.quality
  end

  def test_sulfuras_before_sell_date
    item = update_quality_for_item_with(5, 80, 'Sulfuras, Hand of Ragnaros', 0)
    assert_equal 80, item.quality
  end

  def test_sulfuras_on_sell_date
    item = update_quality_for_item_with(0, 80, 'Sulfuras, Hand of Ragnaros', 0)
    assert_equal 80, item.quality
  end

  def test_sulfuras_after_sell_date
    item = update_quality_for_item_with(-10, 80, 'Sulfuras, Hand of Ragnaros', 0)
    assert_equal 80, item.quality
  end

  def test_backstage_pass_long_before_sell_date
    item = update_quality_for_item_with(11, 10, 'Backstage passes to a TAFKAL80ETC concert')
    assert_equal 11, item.quality
  end

  def test_backstage_pass_medium_close_to_sell_date_upper_bound
    item = update_quality_for_item_with(10, 10, 'Backstage passes to a TAFKAL80ETC concert')
    assert_equal 12, item.quality
  end

  def test_backstage_pass_medium_close_to_sell_date_upper_bound_at_max_quality
    item = update_quality_for_item_with(10, 50, 'Backstage passes to a TAFKAL80ETC concert')
    assert_equal 50, item.quality
  end

  def test_backstage_pass_medium_close_to_sell_date_lower_bound
    item = update_quality_for_item_with(6, 10, 'Backstage passes to a TAFKAL80ETC concert')
    assert_equal 12, item.quality
  end

  def test_backstage_pass_medium_close_to_sell_date_lower_bound_at_max_quality
    item = update_quality_for_item_with(6, 50, 'Backstage passes to a TAFKAL80ETC concert')
    assert_equal 50, item.quality
  end

  def test_backstage_pass_very_close_to_sell_date_upper_bound
    item = update_quality_for_item_with(5, 10, 'Backstage passes to a TAFKAL80ETC concert')
    assert_equal 13, item.quality
  end

  def test_backstage_pass_very_close_to_sell_date_upper_bound_at_max_quality
    item = update_quality_for_item_with(5, 50, 'Backstage passes to a TAFKAL80ETC concert')
    assert_equal 50, item.quality
  end

  def test_backstage_pass_very_close_to_sell_date_lower_bound
    item = update_quality_for_item_with(1, 10, 'Backstage passes to a TAFKAL80ETC concert')
    assert_equal 13, item.quality
  end

  def test_backstage_pass_very_close_to_sell_date_lower_bound_at_max_quality
    item = update_quality_for_item_with(1, 50, 'Backstage passes to a TAFKAL80ETC concert')
    assert_equal 50, item.quality
  end

  def test_backstage_pass_on_sell_date
    item = update_quality_for_item_with(0, 10, 'Backstage passes to a TAFKAL80ETC concert')
    assert_equal 0, item.quality
  end

  def test_backstage_pass_after_sell_date
    item = update_quality_for_item_with(-10, 10, 'Backstage passes to a TAFKAL80ETC concert')
    assert_equal 0, item.quality
  end

  def test_conjured_item_before_sell_date
    skip
    item = update_quality_for_item_with(5, 10, 'Conjured Mana Cake')
    assert_equal 8, item.quality
  end

  def test_conjured_item_at_zero_quality
    skip
    item = update_quality_for_item_with(5, 0, 'Conjured Mana Cake')
    assert_equal 0, item.quality
  end

  def test_conjured_item_on_sell_date
    skip
    item = update_quality_for_item_with(0, 10, 'Conjured Mana Cake')
    assert_equal 6, item.quality
  end

  def test_conjured_item_on_sell_date_at_zero_quality
    skip
    item = update_quality_for_item_with(0, 0, 'Conjured Mana Cake')
    assert_equal 0, item.quality
  end

  def test_conjured_item_after_sell_date
    skip
    item = update_quality_for_item_with(-10, 10, 'Conjured Mana Cake')
    assert_equal 6, item.quality
  end

  def test_conjured_item_after_sell_date_at_zero_quality
    skip
    item = update_quality_for_item_with(-10, 0, 'Conjured Mana Cake')
    assert_equal 0, item.quality
  end

end