Custom flatten function for Citrusbyte application

custom_flatten.rb

require 'rspec'

class Array
  def custom_flatten
    self.reduce([]) do |result, entry|
      entry.kind_of?(Array) ? result += entry.custom_flatten : result << entry
    end
  end
end

RSpec.describe Array do
  it 'flattens [1, 3, 3]' do
    expect([1, 3, 4].custom_flatten).to eq [1, 3, 4]
  end

  it 'flattens [1, [2], 3]' do
    expect([1, [2], 3].custom_flatten).to eq [1, 2, 3]
  end

  it 'flattens [1, 2, [3, 4, [5]]], 6, [7]]' do
    numbers = [1, 2, [3, 4, [5]], 6, [7]]
    expect(numbers.custom_flatten).to eq [1, 2, 3, 4, 5, 6, 7]
  end
end