OO-style FuzzBuzz solution in Ruby

fuzzbuzz.rb

class FuzzBuzz
  attr_reader :n, :fuzzbuzzable

  def initialize(n, fuzzbuzzable)
    @n = n
    @fuzzbuzzable = fuzzbuzzable
  end

  def do_it
    n.times do |i|
      fuzzbuzzable.fuzz(i) if i % 3 == 0
      fuzzbuzzable.buzz(i) if i % 5 == 0
    end
  end
end

class PrintToStdoutFuzzBuzzable
  def fuzz(i)
    puts "#{i}: fuzz"
  end

  def buzz(i)
    puts "#{i}: buzz"
  end
end

if __FILE__ == $0
  fuzzbuzzable = PrintToStdoutFuzzBuzzable.new
  fuzzbuzz = FuzzBuzz.new(100, fuzzbuzzable)
  fuzzbuzz.do_it
end

fuzzbuzz_spec.rb

require_relative 'fuzzbuzz'

shared_examples 'fuzzbuzz duck' do
  let(:duck) { described_class.new }
  it 'implements fuzzbuzz interface' do
    expect(duck).to respond_to(:fuzz, :buzz)
  end
end

describe PrintToStdoutFuzzBuzzable do
  include_examples 'fuzzbuzz duck'
end

describe FuzzBuzz do
  describe '#do_it' do
    it 'performs main algorithm' do
      fuzzbuzzable = instance_double('PrintToStdoutFuzzBuzzable')
      fuzzbuzz = FuzzBuzz.new(16, fuzzbuzzable)
      expect(fuzzbuzzable).to receive(:fuzz).exactly(5).times
      expect(fuzzbuzzable).to receive(:buzz).exactly(3).times
      expect(fuzzbuzzable).to receive(:fuzz).with(15).ordered
      expect(fuzzbuzzable).to receive(:buzz).with(15).ordered
      fuzzbuzz.do_it
    end
  end
end