Find test in cucumber by tag.

test_by_tag.rb

TAG_STRING = /(@\w+\W?)+/
EMPTY_STRING = /^\W*$/

def scan_project(dirname, tag)
  Dir.new(dirname).
    select { |file| File.extname(file) == '.feature' }.
    inject('') { |r, f| r << format_file(f, scan_file(f, tag)) }
end

def format_file(filename, scan_result)
  scan_result.empty? ? '' : ("\n" << filename << "\n" << scan_result)
end

def scan_file(filename, tag)
  return("\n" << File.read(filename)) if tagged_feature?(filename, tag)
  status = :skip
  IO.readlines(filename).inject('') do |result, line|
    case line
    when TAG_STRING
      status, processed_line = *process_tag_line(line, tag)
      result << processed_line
    when EMPTY_STRING
      status = :skip
      result
    else
      result << process_regular_line(line, status)
    end
  end
end

def tagged_feature?(filename, tag)
  has_tag? File.open(filename, &:readline), tag
end

def process_tag_line(line, tag)
  has_tag?(line, tag) ? [:read, "\n" << line] : [:skip, '']
end

def has_tag?(line, tag)
  line.split(' ').include?('@' + tag)
end

def process_regular_line(line, status)
  status == :skip ? '' : line
end

dirname, tag = *ARGV
Dir.chdir dirname
puts scan_project(dirname, tag)