lazy_spec.rb

require 'open3'

class LazySpec
  GIT_CMD   = "git diff --name-only --exit-code"
  RSPEC_CMD = "bundle exec rspec "

  def self.launch
    new.launch
  end

  def launch
    select_files(git_diff)
    summarize
    puts launch_specs
  end

  private

  def git_diff
    stdout, status = Open3.capture2(GIT_CMD)
    stdout
  end

  def select_files(git_diff)
    @files = git_diff.split.select { |file| file.include?("_spec.rb") }
  end

  def summarize
    @files.each { |file| puts "🍺 #{file}" }
  end

  def launch_specs
    stdout, status = Open3.capture2("bundle exec rspec #{@files.join(" ")}")
    stdout
  end
end

LazySpec.launch