Prime number anagram implementation

anagram.rb

require 'prime'
require 'minitest/autorun'

class Anagram
  LETTER_MAP = ('a'..'z').zip(Prime.each).to_h

  def self.anagram?(word_1, word_2)
    word_hash(word_1) == word_hash(word_2)
  end

  def self.word_hash(word)
    word.chars
      .map {|w| LETTER_MAP[w]}
      .reduce(:*)
  end
end

describe Anagram do
  describe 'anagram?' do
    it 'returns true when two words are anagrams' do
      assert Anagram.anagram?('amor', 'roma')
      assert Anagram.anagram?('pai', 'pia')
      assert Anagram.anagram?('seu', 'use')
      assert Anagram.anagram?('alfa', 'fala')
    end

    it 'returns false when two words are not anagrams' do
      refute Anagram.anagram?('amor', 'rome')
      refute Anagram.anagram?('pai', 'piaa')
      refute Anagram.anagram?('seu', 'usse')
      refute Anagram.anagram?('alfa', 'fafa')
    end
  end
end