Array Diff - find additions and deletions between arrays

array_diff.rb

class ArrayDiff
  attr_reader :one, :two

  def initialize one, two
    @one, @two = one.to_a, two.to_a
  end

  def deletions
    one_dup = one.clone
    two.each { |x| one_dup.slice!(one_dup.index(x)) if one_dup.index(x) }
    one_dup
  end

  def additions
    two_dup = two.clone
    one.each { |x| two_dup.slice!(two_dup.index(x)) if two_dup.index(x) }
    two_dup
  end
end

describe ArrayDiff do
  let(:array_diff) { ArrayDiff.new [1, 2, 2, 3, 6, 6, 7, 7, 7],
                                   [2, 3, 3, 4, 8, 9] }

  describe '#deletions' do
    it 'returns array of deletions' do
      expect(array_diff.deletions).to eq [1, 2, 6, 6, 7, 7, 7]
    end
  end

  describe '#additions' do
    it 'returns array of additions' do
      expect(array_diff.additions).to eq [3, 4, 8, 9]
    end
  end
end