Quick-and-dirty autotest without installing Autotest

autotest.rb

#!/usr/bin/env ruby

class Autotester
  MONITOR_MATCH_PATTERN = "**/*.rb"
  TEST_COMMAND = "rspec spec"

  def cache
    @cache ||= {}
  end

  def rerun
    system TEST_COMMAND
  end

  def timestamp(file)
    File.file?(file) && File.stat(file).mtime.to_f
  end

  def build_cache
    cache.clear
    Dir[MONITOR_MATCH_PATTERN].each do |fi|
      cache[fi] = timestamp(fi)
    end
  end

  def changed?(fi)
    !cache.key?(fi) || cache[fi] != timestamp(fi)
  rescue
    cache.delete(fi)
    true
  end

  def start!
    while true
      Dir[MONITOR_MATCH_PATTERN].each do |fi|
        if changed?(fi)
          rerun
          build_cache
          break # don't want to run for each file
        end
      end

      sleep(1)
    end
  end
end

Autotester.new.start!