coin_changer.rb

class CoinChanger
  def self.change(amount)
    change = []
    [25,10,5,1].each do |coin|
      while amount >= coin
        change << coin
        amount -= coin
      end
    end
    change
  end
end

coin_changer_spec.rb

require 'rspec'
require 'coin_changer'

describe(CoinChanger) do
  [
    [1, [1]],
    [2, [1,1]],
    [3, [1,1,1]],
    [5, [5]],
    [6, [5,1]],
    [7, [5,1,1]],
    [10, [10]],
    [11, [10,1]],
    [15, [10,5]],
    [20, [10,10]],
    [25, [25]],
    [50, [25,25]],
    [94, [25,25,25,10,5,1,1,1,1]]
  ].each do |amount, expected|
    it "changes #{amount} to #{expected}" do
      expect(CoinChanger.change(amount)).to eq(expected)
    end
  end
end