Binary search for order-dependent test failures

binary_search_specs.rb

#!/usr/bin/env ruby

specs_in_order = File.read('spec_order').split

failing_spec = ARGV.first

specs = specs_in_order[0...specs_in_order.index(failing_spec)]

suspects = specs

while suspects.length > 1 do
  count = suspects.length
  # Try the first half
  specs_to_run = suspects[0...(count/2)]
  puts "Trying #{suspects.join(' ')}"
  start = Time.now
  system("rspec #{specs_to_run.join(' ')} #{failing_spec}")
  puts "Finished in #{Time.now - start} seconds"
  if $? == 0
    puts "Innocent!"
    # This group is innocent. The culprit is in the other half.
    suspects = suspects[(count/2)..-1]
  else
    puts "Guilty!"
    # One of these is guilty.
    suspects = specs_to_run
  end
end

puts "The culprit is #{suspects.first}"

Create a file in the local directory called 'spec_order', with the list of specs in the order they were run to cause the failure. Pass as an argument to the program the path to the failing spec.