Custom instance method of Array class in Ruby to flatten it

array.rb

class Array

  def flatten_it(result = [])
    self.each do |value|
      value.is_a?(Array) ? value.flatten_it(result) : (result << value)
    end
    result
  end

end

array_test.rb

require 'minitest/autorun'
require './array'

describe Array do

  before do
    @nested_array = [1, [1,2],[3,[4,5],[]]]
  end
  
  describe "#flatten_it" do

    it "returns a flattened array" do
      assert_equal [1,1,2,3,4,5], @nested_array.flatten_it
    end

    test_cases = [
      [ 1, 1, 1, 1, 1, 1, 1, 1 ],
      [[3,4,[],5],5],
      [:apple, :banana, [1,[]], 'brocolli'],
      [],
      [nil, nil, [[[1]]]],
      [[1,2,[3]],4],
      [1,2,3,"banana",[1,2,3],[]]
    ]

    test_cases.each do |arr|

      it "#{arr}.flatten_it should not have a nested array" do
        assert arr.flatten_it.none? {|v| v.is_a? Array}
      end

      it "#{arr}.flatten it should match ruby's flatten method" do
        assert_equal arr.flatten, arr.flatten_it
      end

    end

  end

end