早上看了
Ruby論壇中有人（blackanger）寫的TDD by Ex這本書里的資金例子，自己也想寫一寫。和他不同，我是全過程詳細寫出來。第一次用Ruby寫代碼，第一次用Ruby的Unit框架，而且下午睡醒后迷迷糊糊寫的，可能有很多錯誤，請多多指正。
第一次迭代后的代碼（簡單的TDD代碼）
#?file?tc_doller.rb
$:.unshift?File.join(File.dirname(__FILE__),?"..",?"src")
require?'test/unit'
require?'dollar'
class?TestMoney?<?Test::Unit::TestCase
????????def?testMultiplication
????????????????five?=?Dollar.new(5)
????????????????five.times(2)
????????????????assert_equal(10,?five.amount)
????????end
end
#?file?doller.rb
class?Dollar
????????def?initialize(amount)
????????????????@amount?=?amount
????????end
????????
????????def?times(multiplier)
????????????????@amount?=?@amount?*?multiplier
????????end
????????
????????def?amount
????????????????return?@amount
????????end
end
第二次迭代后的代碼
#?file?tc_doller.rb
$:.unshift?File.join(File.dirname(__FILE__),?"..",?"src")
require?'test/unit'
require?'dollar'
class?TestMoney?<?Test::Unit::TestCase
????????def?testMultiplication
????????????????five?=?Dollar.new(5)
????????????????product?=?five.times(2)
????????????????assert_equal(10,?product.amount)
????????????????product?=?five.times(3)
????????????????assert_equal(15,?product.amount)
????????end
end
#?file?doller.rb
class?Dollar
????????attr_reader?:amount
????????protected?:amount
????????
????????def?initialize(amount)
????????????????@amount?=?amount
????????end
????????
????????def?times(multiplier)
????????????????return?Dollar.new?@amount?*?multiplier
????????end
end
第三，四次迭代后的代碼（添加了相等性測試，剛好Ruby中的equal?和==的語意和Java相反）
#?file?tc_doller.rb
$:.unshift?File.join(File.dirname(__FILE__),?"..",?"src")
require?'test/unit'
require?'dollar'
class?TestMoney?<?Test::Unit::TestCase
????????def?testMultiplication
????????????????five?=?Dollar.new(5)
????????????????product?=?five.times(2)
????????????????assert_equal(10,?product.amount)
????????????????product?=?five.times(3)
????????????????assert_equal(15,?product.amount)
????????end
????????
????????def?testEquality
????????????????assert(Dollar.new(5)?==?Dollar.new(5))
????????????????assert(Dollar.new(5)?!=?Dollar.new(6))
????????end
????????
end
#?file?doller.rb
class?Dollar
????????attr_reader?:amount
????????protected?:amount
????????
????????def?initialize(amount)
????????????????@amount?=?amount
????????end
????????
????????def?times(multiplier)
????????????????return?Dollar.new?@amount?*?multiplier
????????end
????????
????????def?==(obj)
????????????????return?obj.amount?==?@amount
????????end
end
第五，六，七次迭代后的代碼（短命的Franc對象登場）
#?file?tc_doller.rb
$:.unshift?File.join(File.dirname(__FILE__),?"..",?"src")
require?'test/unit'
require?'money'
require?'dollar'
require?'franc'
class?TestMoney?<?Test::Unit::TestCase
????????def?testMultiplication
????????????????five?=?Dollar.new(5)
????????????????assert_equal(Dollar.new(10),?five.times(2))
????????????????assert_equal(Dollar.new(15),?five.times(3))
????????end
????????
????????def?testEquality
????????????????assert(Dollar.new(5)?==?Dollar.new(5))
????????????????assert(Dollar.new(5)?!=?Dollar.new(6))
????????????????assert(Franc.new(5)?==?Franc.new(5))
????????????????assert(Franc.new(5)?!=?Franc.new(6))
????????????????assert(Franc.new(5)?!=?Dollar.new(5))
????????end
????????
????????def?testFrancMultiplication
????????????????five?=?Franc.new(5)
????????????????assert_equal(Franc.new(10),?five.times(2))
????????????????assert_equal(Franc.new(15),?five.times(3))
????????end
end
#?file?doller.rb
class?Dollar?<?Money
????????def?initialize(amount)
????????????????super(amount)
????????end
????????
????????def?times(multiplier)
????????????????return?Dollar.new(@amount?*?multiplier)
????????end
end
#?file?franc.rb
class?Franc?<?Money
????????def?initialize(amount)
????????????????super(amount)
????????end
????????
????????def?times(multiplier)
????????????????return?Franc.new(@amount?*?multiplier)
????????end
end
#?file?money.rb
class?Money
????????attr_reader?:amount
????????protected?:amount
????????
????????def?initialize(amount)
????????????????@amount?=?amount
????????end
????????
????????def?==(obj)
????????????????return?obj.amount.equal?(@amount)
????????end
end
第八，九，十，十一次迭代（消除子類，很巧妙的一步）
#?file?tc_doller.rb
$:.unshift?File.join(File.dirname(__FILE__),?"..",?"src")
require?'test/unit'
require?'money'
class?TestMoney?<?Test::Unit::TestCase
????????def?testMultiplication
????????????????five?=?Money.dollar(5)
????????????????assert_equal(Money.dollar(10),?five.times(2))
????????????????assert_equal(Money.dollar(15),?five.times(3))
????????end
????????
????????def?testFrancMultiplication
????????????????five?=?Money.franc(5)
????????????????assert_equal(Money.franc(10),?five.times(2))
????????????????assert_equal(Money.franc(15),?five.times(3))
????????end
????????
????????def?testEquality
????????????????assert(Money.dollar(5)?==?Money.dollar(5))
????????????????assert(Money.dollar(5)?!=?Money.dollar(6))
????????????????assert(Money.franc(5)?!=?Money.dollar(5))
????????end
????????
????????def?testCurrency
????????????????assert_equal("USD",?Money.dollar(1).currency)
????????????????assert_equal("CHF",?Money.franc(1).currency)
????????end????????
end
#?file?money.rb
class?Money
????????attr_reader?:amount,?:currency
????????protected?:amount
????????
????????def?initialize(amount,?currency)
????????????????@amount?=?amount
????????????????@currency?=?currency
????????end
????????
????????def?self.dollar(amount)
????????????????return?Money.new(amount,?"USD")
????????end
????????
????????def?self.franc(amount)
????????????????return?Money.new(amount,?"CHF")
????????end
????????
????????def?times(multiplier)
????????????????return?Money.new(@amount*multiplier,?@currency)
????????end
????????
????????def?plus(addend)
????????????????return?Money.new(@amount?+?addend.amount,?currency)
????????end
????????
????????def?==(obj)
????????????????return?obj.amount.equal?(@amount)?&&?(obj.currency?==?@currency)
????????end
end
最后的一部分
最后是完成不同貨幣之間的計算，引入了兩個新的對象負責處理匯率的Bank和貨幣相加的Sum對象。
由于Ruby的動態性無須讓Sum和Money實現同一接口，反正原書中的Expression對象也是為了Sum和Money對象可以通信。或許可以把Sum簡化掉，有空時再想想。
#?file?tc_doller.rb
$:.unshift?File.join(File.dirname(__FILE__),?"..",?"src")
require?'test/unit'
require?'money'
require?'bank'
require?'sum'
class?TestMoney?<?Test::Unit::TestCase
????def?testDollarMultiplication
????????five?=?Money.dollar(5)
????????assert_equal(Money.dollar(10),?five.times(2))
????????assert_equal(Money.dollar(15),?five.times(3))
????end
????
????def?testFrancMultiplication
????????five?=?Money.franc(5)
????????assert_equal(Money.franc(10),?five.times(2))
????????assert_equal(Money.franc(15),?five.times(3))
????end
????
????def?testEquality
????????assert(Object.new?!=?Money.dollar(1))
????????assert(Money.dollar(5)?==?Money.dollar(5))
????????assert(Money.dollar(5)?!=?Money.dollar(6))
????????assert(Money.franc(5)?!=?Money.dollar(5))
????end
????
????def?testCurrency
????????assert_equal("USD",?Money.dollar(1).currency)
????????assert_equal("CHF",?Money.franc(1).currency)
????end
????
????def?testSimpleAddition
????????five?=?Money.dollar(5)
????????sum?=?five.plus(Money.dollar(5))
????????bank?=?Bank.new()
????????reduced?=?bank.reduce(sum,?"USD")
????????assert_equal(Money.dollar(10),?reduced)
????end
????
????def?testReduceSum
????????sum?=?Sum.new(Money.dollar(3),?Money.dollar(4))
????????bank?=?Bank.new()
????????result?=?bank.reduce(sum,?"USD")
????????assert_equal(Money.dollar(7),?result)
????end
????
????def?testReduceMoney
????????bank?=?Bank.new
????????result?=?bank.reduce(Money.dollar(1),?"USD")
????????assert_equal(Money.dollar(1),?result)
????end
????
????def?testReduceMoneyDiffentCurrency
????????bank?=?Bank.new
????????bank.addRate("CHF",?"USD",?2)
????????result?=?bank.reduce(Money.franc(2),?"USD")
????????assert_equal(Money.dollar(1),?result)
????end
????
????def?testIndentityRate
????????bank?=?Bank.new
????????bank.addRate("USD",?"CHF",?0.5)
????????assert_equal(1,?bank.rate("USD",?"USD"))
????????assert_equal(0.5,?bank.rate("USD",?"CHF"))
????????assert_equal(2,?bank.rate("CHF",?"USD"))
????end
????
????def?testMixedAddition
????????fiveBucks?=?Money.dollar(5)
????????tenFrancs?=?Money.franc(10)
????????bank?=?Bank.new
????????bank.addRate("CHF",?"USD",?2)
????????result?=?bank.reduce(fiveBucks.plus(tenFrancs),?"USD")
????????assert_equal(Money.dollar(10),?result)
????end
????
????def?testSumTimes
????????fiveBucks?=?Money.dollar(5)
????????tenFrancs?=?Money.franc(10)
????????bank?=?Bank.new
????????bank.addRate("CHF",?"USD",?2)
????????sum?=?Sum.new(fiveBucks,?tenFrancs).times(2)
????????result?=?bank.reduce(sum,?"USD")
????????assert_equal(Money.dollar(20),?result)
????end
end
#?file?money.rb
class?Money
????attr_reader?:amount,?:currency
????
????def?initialize(amount,?currency)
????????@amount?=?amount
????????@currency?=?currency
????end
????
????def?self.dollar(amount)
????????return?Money.new(amount,?"USD")
????end
????
????def?self.franc(amount)
????????return?Money.new(amount,?"CHF")
????end
????
????def?times(multiplier)
????????return?Money.new(@amount*multiplier,?@currency)
????end
????
????def?plus(addend)
????????return?Sum.new(self,?addend)
????end
????
????def?==(obj)
????????return?obj.amount.equal?(@amount)?&&?(obj.currency?==?@currency)
????end
????
????def?reduce(bank,?to)
????????rate?=?bank.rate(@currency,?to)
????????return?Money.new(@amount?/?rate,?to)
????end
end
#?file?bank.rb
class?Bank
????attr_accessor?:rates
????@@rates?=?{}
????
????def?reduce(source,?to)
????????return?source.reduce(self,?to)
????end
????
????def?addRate(from,?to,?rate)
????????@@rates["#{from}-#{to}"]?=?rate
????????@@rates["#{to}-#{from}"]?=?1?/?rate
????end
????
????def?rate(from,?to)
????????return?1?if(from?==?to)
????????return?@@rates["#{from}-#{to}"]
????end
end
#?file?sum.rb
class?Sum
????attr_reader?:augend,?:addend
????
????def?initialize(augend,?addend)
????????@augend?=?augend
????????@addend?=?addend
????end
????
????def?reduce(bank,?to)
????????amount?=?augend.reduce(bank,?to).amount?+?addend.reduce(bank,?to).amount
????????return?Money.new(amount,?to)
????end
????
????def?times(multiplier)
????????return?Sum.new(augend.times(multiplier),?addend.times(multiplier))
????end
end