bank2.rb

# Learning Ruby. A consice implementation of the Bank Account example.
# http://gist.github.com/277023 

require 'test/unit'

class Account
  attr_reader :number, :name, :balance
  
  @@number = 0
  
  def initialize(name)
    @number  = @@number += 1   
    @name    = name 
    @balance = 0
  end
  
  def deposit(amount)
    @balance += amount
  end
  
  def withdraw?(amount)
    return false if amount > @balance
    @balance -= amount
    true
  end
  
  def calculate_interest(rate)
    12.times.inject(@balance) { |b, m| b += b * rate } - @balance
  end
end

class TransactionAccount < Account
  TRANSACTION_FEE = 0.30
  
  def withdraw?(amount)
    return false unless super(amount)
    @balance -= TRANSACTION_FEE
    true
  end
end

class TestAccount < Test::Unit::TestCase
  def setup
    @account1 = Account.new('Monica')
  end
  
  def test_number_should_be_incremented_at_initialization
    assert @account1.number < @account2.number
  end
  
  def test_name_should_be_defined_at_initialization
    assert_equal 'Monica', @account1.name
  end
  
  def test_balance_should_be_zero_at_initialization
    assert @account1.balance.zero?
  end
  
  def test_deposit_should_increase_balance
    @account1.deposit(100)
    assert_equal 100, @account1.balance
  end
  
  def test_withdraw_should_be_false_when_insufficient_balance
    assert ! @account1.withdraw?(150)
  end
  
  def test_withdraw_should_be_true_when_sufficient_balance
    @account1.deposit(100)
    assert @account1.withdraw?(25)
    assert_equal 75, @account1.balance
  end
  
  def test_calculate_interest
    @account1.deposit(100)
    assert_equal '79.5856326022129', @account1.calculate_interest(0.05).to_s
  end
end

class TestTransactionAccount < Test::Unit::TestCase
  def test_withdraw_should_charge_transaction_fee
    @account1 = TransactionAccount.new('Monica')
    @account1.deposit(100)
    @account1.withdraw?(100)
    assert_equal -0.30, @account1.balance
  end
end