find_ordering_problem.rb

#!/usr/bin/env ruby 

class FailFinder
  def initialize(specs)
    @test_specs = specs[0...-1]
    @result_spec = specs.last
  end

  def stupid_spec
    binary_search(@test_specs)
  end
  
  private
  def specs_fail(specs)
    result = `rspec #{specs.join(' ')} #{@result_spec}`
    p "#{result}\n"
    result.match(/Failure/)
  end
  
  def binary_search(array)
    p "#{array}\n"

    if array.length == 1
      return array[0]
    end
    
    mid = array.length / 2
    
    if specs_fail(array[0...mid])
      binary_search(array[0...mid])
    else
      binary_search(array[mid...array.length])
    end
  end
end

p "The failure is: #{FailFinder.new(ARGV).stupid_spec}"