flatten.rb

module Flattener
  def flatten element, result=[]
    if element.is_a? Array
      element.each do |e|
        flatten e, result
      end
    else
      result << element
    end
    result
  end
end

require "minitest/autorun"

class TestFlattener < Minitest::Test

  include Flattener

  def test_empty
    assert_equal [], flatten([])
  end

  def test_single
    assert_equal [1], flatten([1])
  end

  def test_multiple
    assert_equal [3,4,1,2], flatten([3,4,1,2])
  end

  def test_nested
    assert_equal [3,4,1,2], flatten([[3,4,[1]],2])
    assert_equal [3,4,1,2], flatten([3,4,[[1],2]])
    assert_equal [1,4,1,2,4], flatten([1,4,[[1],2],4])
  end
end