MiniTestで一つのファイルにテストを混ぜてしまおう ref: http://qiita.com/esehara@github/items/40a74251b0a67b5b6520

file0.txt

# もっといい方法があるが、サンプルのために、このままにする
def exchange_node x, coin
  return 1 if x == 0
  return 1 if x < 5
  return 0 if x < 0

  sum_coin = 0
  case coin
  when 10
    sum_coin += exchange_node(x - 5, 5)
  end
  sum_coin += exchange_node(x - coin, coin) + 1
  return sum_coin
end

# --------------------TestCase
require 'minitest/unit'
require 'minitest/autorun'

class TestExchange < MiniTest::Unit::TestCase
  def test_exchange_node_5
    assert_equal 3, exchange_node(10, 5)
  end

  def test_exchange_node_10
    assert_equal 4, exchange_node(10, 10)
  end
end

file1.txt

esehara@esehara-CF-N9JCCCPS:~/Code/Ruby/ExchangeProblem$ ruby exchange.rb
Run options: --seed 4701

# Running tests:

..

Finished tests in 0.016379s, 305.2619 tests/s, 305.2619 assertions/s.

2 tests, 2 assertions, 0 failures, 0 errors, 0 skips

file2.txt

irb(main):001:0> require './exchange.rb'
=> true