implementation of Array#flatten in ruby

flatten.rb

# implementation of Array#flatten with ruby
def flatten arr
  return arr unless arr.is_a? Array

  arr.reduce([]) do |out, item|
    out.push *flatten(item)
  end
end


if __FILE__ == $0
  # gem install minitest
  # gem install minitest-reporters
  require 'minitest/autorun'
  require 'minitest/reporters'

  describe method(:flatten) do

    it "works with one level depth array" do
      flatten([1]).must_equal [1]
      flatten([1, 10]).must_equal [1, 10]
    end

    it "works with two level depth array" do
      flatten([[1]]).must_equal [1]
      flatten([1, [2]]).must_equal [1, 2]
      flatten([[1], 2]).must_equal [1, 2]
      flatten([[1], [2]]).must_equal [1, 2]
    end

    it "works with more level depth array" do
      flatten([1, [1, [2, [3]]]]).must_equal [1, 1, 2, 3]
    end
  end

end