テスト駆動開発入門をRubyで写経してみた。9

9章で実施したこと

• DollarクラスとFrancクラスのコンストラクタを共通化
• 通貨単位を返すcurrencyアクセサの実装
• *()メソッド内でのファクトリメソッドの使用

money.rb

#!/usr/bin/ruby
#coding: utf-8
# テスト駆動開発入門9章 生きている時(times)
class Money
  attr_accessor :amount, :currency
  protected :amount

  def initialize(amount, currency)
    @amount = amount
    @currency = currency
  end

  def ==(other)
    return @amount == other.amount && self.class == other.class
  end

  def self.franc(amount)
    return Franc.new(amount, "CHF")
  end

  def self.dollar(amount)
    return Dollar.new(amount, "USD")
  end
end

class Dollar < Money
  def *(multiplier)
    return Money.dollar(@amount * multiplier)
  end
end

class Franc < Money
  def *(multiplier)
    return Money.franc(@amount * multiplier)
  end
end

money_test.rb

#!/usr/bin/ruby
#coding: utf-8
# テスト駆動開発入門9章 生きている時(times)
require 'test/unit'
require 'money'

class TestMoney < Test::Unit::TestCase
  def test_multiplication
    five = Money.dollar(5)
    assert_equal(Money.dollar(10), five * 2)
    assert_equal(Money.dollar(15), five * 3)
  end

  def test_equality
    assert(Money.dollar(5) == Money.dollar(5))
    assert(Money.dollar(5) != Money.dollar(6))
    assert(Money.franc(5)  == Money.franc(5))
    assert(Money.franc(5)  != Money.franc(6))
    assert(Money.dollar(5) != Money.franc(5))
  end

  def test_Franc_multiplication
    five = Money.franc(5)
    assert_equal(Money.franc(10), five * 2)
    assert_equal(Money.franc(15), five * 3)
  end

  def test_currency
    assert_equal("USD", Money.dollar(1).currency)
    assert_equal("CHF", Money.franc(1).currency)
  end
end