buck_fizz.rb

class BuckFizz
  def print
    all.each do |buck_fizz|
      puts buck_fizz
    end
  end
  
  private
  
  def all
    1.upto(100).map do |number|
      case
      when number % 15 == 0 then "BucksFizz"
      when number % 3  == 0 then "Bucks"
      when number % 5  == 0 then "Fizz"
      else number
      end
    end
  end
end

buck_fizz_spec.rb

describe BuckFizz do
  describe "#print" do
    it "prints FizzBucks correctly" do
      expect{ BuckFizz.new.print }.to output(start_with(
        %w(1 2 Bucks 4 Fizz Bucks 7 8 Bucks Fizz 11 Bucks 13 14 BucksFizz 16).join("\n")
      )).to_stdout
    end
  end
end