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目の前に僕らの道がある

勉強会とか、技術的にはまったことのメモ

テスト駆動開発入門をPythonで写経してみた。15

とりあえずコードだけ。

money.py

#!/usr/bin/env python
# coding: utf-8
"""テスト駆動開発入門 15章 通貨の混合
"""

class Expression(object):
    def reduce(self, bank, currency_to):
        raise NotImplementedError

    def __add__(self, addend):
        raise NotImplementedError

class Money(Expression):
    def __init__(self, amount, currency):
        self._amount = amount
        self._currency = currency

    def __mul__(self, multiplier):
        """原書のtimesメソッド
        """
        return Money(self._amount * multiplier, self._currency)

    @staticmethod
    def dollar(amount):
        return Money(amount, "USD")

    @staticmethod
    def franc(amount):
        return Money(amount, "CHF")

    def currency(self):
        return self._currency

    def reduce(self, bank, currency_to):
        rate = bank.rate(self._currency, currency_to)
        return Money(self._amount/rate, currency_to)

    def __eq__(self, other):
        """原書のequalsメソッド
        """
        return self._amount == other._amount and \
                self.currency() == other.currency()

    def __str__(self):
        """デバッグ用出力文字列
        """
        return str(self._amount) + " " + str(self._currency)

    __unicode__ = __str__
    __repr__ = __str__

    def __add__(self, addend):
        """原書のplusメソッド
        """
        return Sum(self, addend)

class Bank(object):
    def __init__(self):
        self.rates = dict()

    def reduce(self, source, currency_to):
        return source.reduce(self, currency_to)

    def rate(self, currency_from, currency_to):
        if currency_from == currency_to:
            return 1
        return self.rates[(currency_from, currency_to)]

    def add_rate(self, currency_from, currency_to, rate):
        self.rates[(currency_from, currency_to)] = rate
        # Hashtableをdictionaryで実装

class Sum(Expression):
    def __init__(self, augend, addend):
        self.augend = augend
        self.addend = addend

    def reduce(self, bank, currency_to):
        amount = self.augend.reduce(bank, currency_to)._amount + \
                self.addend.reduce(bank, currency_to)._amount
        return Money(amount, currency_to)

    def __add__(self, addend):
        return None

money_test.py

#!/usr/bin/env python
# coding: utf-8
"""テスト駆動開発入門 15章 通貨の混合
"""

import unittest
from money import *

class TestMoney(unittest.TestCase):
    """moneyモジュールのテスト
    """

    def testMultiplication(self):
        """かけ算のテスト
        """
        five = Money.dollar(5)
        self.assertEqual(Money.dollar(10), five * 2)
        self.assertEqual(Money.dollar(15), five * 3)

    def testFrancMultiplication(self):
        """Francクラスのかけ算のテスト
        """

        five = Money.franc(5)
        self.assertEqual(Money.franc(10), five * 2)
        self.assertEqual(Money.franc(15), five * 3)

    def testEuality(self):
        """同値テスト
        """

        self.assert_(    Money.dollar(5) == Money.dollar(5) )
        self.assert_(not Money.dollar(5) == Money.dollar(6) )
        self.assert_(not Money.franc(5)  == Money.dollar(5) )

    def testCurrency(self):
        """通貨単位のテスト
        """

        self.assertEqual("USD", Money.dollar(1).currency() )
        self.assertEqual("CHF", Money.franc(1).currency() )

    def testSimpleAddition(self):
        """足し算のテスト
        """

        five = Money.dollar(5)
        sum = five + five
        self.assert_(Money.dollar(10), sum)
        bank = Bank()
        reduced = bank.reduce(sum, "USD")
        self.assertEqual(Money.dollar(10), reduced)

    def testPlusReturnsSum(self):
        five = Money.dollar(5)
        result = five + five
        sum = result
        self.assertEqual(five, sum.addend)
        self.assertEqual(five, sum.augend)

    def testReduceSum(self):
        sum = Sum(Money.dollar(3), Money.dollar(4) )
        bank = Bank()
        result = bank.reduce(sum, "USD")
        self.assertEqual(Money.dollar(7), result)

    def testReduceMoney(self):
        bank = Bank()
        result = bank.reduce(Money.dollar(1), "USD")
        self.assertEqual(Money.dollar(1), result)

    def testReduceMoneyDifferentCurrency(self):
        bank = Bank()
        bank.add_rate("CHF", "USD", 2)
        result = bank.reduce(Money.franc(2), "USD")
        self.assertEqual(Money.dollar(1), result)

    def testIdentityRate(self):
        self.assertEqual(1, Bank().rate("USD", "USD") )

    def testMixedAddition(self):
        five_bucks = Money.dollar(5)
        ten_francs = Money.franc(10)
        bank = Bank()
        bank.add_rate("CHF", "USD", 2)
        result = bank.reduce(five_bucks + ten_francs, "USD")
        self.assertEqual(Money.dollar(10), result)

if __name__ == "__main__":
    unittest.main()