quiz.rb

# use a single string object as IO, enforces ordering, use srand to avoid randomness and stubbing/subclassing
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
    puts answer
    if answer.to_i == first + second
      @output.puts "Correct!"
    else
      @output.puts "Incorrect!"
    end
  end
end
 
require "test/unit"
class QuizTest < Test::Unit::TestCase
  def mkIO(s)
    def s.puts(str)
      def self.gets
         self 
      end
      concat(str)
    end
    s
  end
  def test_correct
    srand(10)
    io=mkIO("13\n")
    Quiz.new(io,io).problem
    assert_equal("13\nWhat is 9 + 4?Correct!",io)
  end
  
  def test_incorrect
    srand(10)
    io=mkIO("14\n")
    Quiz.new(io,io).problem
    assert_equal("14\nWhat is 9 + 4?Incorrect!",io)
  end
end