Ruby: Anagram detector class - way cleaner than my old one

anagram.rb

class Anagram
  def initialize(anagram)
    @anagram = anagram
  end

  def match(words)
    words.select do |word|
      is_anagram?(word)
    end
  end

  def is_anagram?(word)
    word.chars.sort == @anagram.chars.sort
  end
end

anagrams_spec.rb

# Anagram Detector

# Write a program that, given a word and a list of possible anagrams, 
# selects the correct one(s).

# In other words, given: "listen" and %w(enlists google inlets banana) 
# the program should return "inlets".

# PS what is %w? 
# http://stackoverflow.com/questions/1274675/ruby-what-does-warray-mean

# Save this file as anagram_spec.rb
# run it with rspec anagram_spec.rb

RSpec.configure do |config|
  # Use color in STDOUT
  config.color_enabled = true

  # Use color not only in STDOUT but also in pagers and files
  config.tty = true

  # Use the specified formatter
  config.formatter = :progress # :progress, :html, :textmate
end

require_relative './anagram'

describe 'Anagram' do 
  it 'should detect no matches' do
    detector = Anagram.new('diaper')
    detector.match(%w(hello world zombies pants)).should eq([])
  end

  it 'should detect a simple anagram' do
    detector = Anagram.new('ba')
    anagrams = detector.match(['ab', 'abc', 'bac'])
    anagrams.should eq(['ab'])
  end

  it 'should detect an anagram' do
    detector = Anagram.new('listen')
    anagrams = detector.match %w(enlists google inlets banana)
    anagrams.should eq(['inlets'])
  end

  it 'should detect multiple anagrams' do
    detector = Anagram.new('allergy')
    anagrams = detector.match %w(gallery ballerina regally clergy largely leading)
    anagrams.should eq(['gallery', 'regally', 'largely'])
  end
end