Ryan Bates community challenge solution

quiz.rb

# COMMUNITY CHALLENGE
#
# How would you test this Quiz#problem method? Only two rules:
#
# 1. You must test the order the gets/puts happen. The tests should not
#    still pass if "gets" happens before "puts", etc.
#
# 2. No changing the Quiz class implementation/structure. But you can
#    use whatever framework you want for the tests.
# 
# Note: The first rule used to be "no mocking" but I changed it. If you
#       can accomplish the first rule with mocks then go ahead. I'm looking
#       for the simplest/cleanest solution whatever that may be.
#
class Quiz
  def initialize(input = STDIN, output = STDOUT)
    @input = input
    @output = output
  end
  
  def problem
    first = rand(10)
    second = rand(10)
    @output.puts "What is #{first} + #{second}?"
    answer = @input.gets
    if answer.to_i == first + second
      @output.puts "Correct!"
    else
      @output.puts "Incorrect!"
    end
  end
end

require "test/unit"
require "stringio"
require "rubygems"
require "mocha"

# special StringIO with a separate read cursor that can
# be used to re-read the IO from beginning unobtrusively
class RereadableStringIO < StringIO
  def initialize(*args)
    super
    @read_pos = pos
  end
  
  def rereading
    old_pos = pos
    begin
      seek @read_pos
      result = yield self
      @read_pos = pos
      return result
    ensure
      seek old_pos
    end
  end
  
  def reread
    rereading { read }
  end
end

# mocks a STDIN; only supports `gets`
class FakeInput
  def initialize
    @responses = []
  end
  
  def push(*args, &block)
    val = args.empty?? block : args.first
    @responses.push(val)
  end
  
  def gets
    val = @responses.pop
    val.respond_to?(:call) ? val.call : val
  end
end
  
class QuizTest < Test::Unit::TestCase
  def setup
    @input = FakeInput.new
    @output = RereadableStringIO.new
  end
  
  def test_correct
    @input.push {
      question = @output.reread
      _, first, second = question.match(/^What is (\d+) \+ (\d+)\?\n$/).to_a
      (first.to_i + second.to_i).to_s + $/
    }
    
    quiz = Quiz.new(@input, @output)
    quiz.problem
    assert_equal "Correct!\n", @output.reread
  end
  
  def test_incorrect
    @input.push("-1#{$/}")
    
    quiz = Quiz.new(@input, @output)
    quiz.problem
    @output.rereading { |io| io.gets }
    assert_equal "Incorrect!\n", @output.reread
  end
end