Simple List Kata

gistfile1.rb

require 'test/unit'

class List
  def add(item)
    new_item = Item.new(item, @tail)
    @tail = new_item
  end
  
  def delete(item)
    if item == @tail
      @tail = item.next
      return
    end
    
    val = @tail
    prev = nil
    until val == item
      prev = val
      val = val.next
    end
    prev.next = val.next unless val.nil?
  end
  
  def find(item)
    return nil unless @tail
    val = @tail
    until val.nil?
      return val if val.value == item
      val = val.next
    end
  end
  
  def values
    vals = []
    val = @tail
    until val.nil?
      vals.insert(0, val.value)
      val = val.next
    end
    vals
  end
  
  class Item
    attr_reader :value, :next
    attr_writer :next
    def initialize(value, next_item = nil)
      @value = value
      @next = next_item
    end
  end
end

class ListTest < Test::Unit::TestCase
  def test_behavior
    list = List.new
    assert_nil(list.find("fred"))
    list.add("fred")
    assert_equal("fred", list.find("fred").value())
    assert_nil(list.find("wilma"))
    list.add("wilma")
    assert_equal("fred",  list.find("fred").value())
    assert_equal("wilma", list.find("wilma").value())
    assert_equal(["fred", "wilma"], list.values())

    list = List.new
    list.add("fred")
    list.add("wilma")
    list.add("betty")
    list.add("barney")
    assert_equal(["fred", "wilma", "betty", "barney"], list.values())
    list.delete(list.find("wilma"))
    assert_equal(["fred", "betty", "barney"], list.values())
    list.delete(list.find("barney"))
    assert_equal(["fred", "betty"], list.values())
    list.delete(list.find("fred"))
    assert_equal(["betty"], list.values())
    list.delete(list.find("betty"))
    assert_equal([], list.values())
  end
end