Listing 1. atf-sinatra.rb

#!/usr/bin/env ruby

require 'rubygems'
require 'sinatra'
require 'erb'

get '/' do
 @first_number = rand(5000)
 @second_number = rand(@first_number)
 @operation = %w(+ - *).sample
 erb :index
end

post '/answer' do
 @first_number = params[:first_number].to_i
 @second_number = params[:second_number].to_i
 @operation = params[:operation].to_s

 @user_answer = params[:user_answer].to_i
 @right_answer = @first_number.send(@operation, @second_number)

 erb :answer
end