runner.rb

module FizzBuzz
  
  # ...

  def run
    1.upto(100) do |number|
      puts fizz_buzz(number)
    end
  end
end

runner_spec.rb

  describe ".run" do
    full_fizz_buzz = <<~FIZZY 
    1
    2
    Fizz
    .. much more ...
    98
    Fizz
    Buzz
    FIZZY

    it "does a full run integration style" do
      expect { FizzBuzz.run() }.to output(full_fizz_buzz).to_stdout
    end
  end