A custom implementation of Array#flatten

custom_flatten.rb

RSpec.describe "Custom implementation of Array Flatten" do
  it 'flattens array containing empty array' do
    list = [[]]
    expect(custom_flatten(list)).to eq([])
  end

  it 'flattens array containing array with one element' do
    list = [[1]]
    expect(custom_flatten(list)).to eq([1])
  end

  it 'flattens array with two sub arrays' do
    list = [[],[1,2,3,[4]]]
    expect(custom_flatten(list)).to eq([1,2,3,4])
  end

  it 'flattens deeply nested array' do
    list = [[[]],[[4,5,[1, [2,3,[4,5,6,[7,8,9]]]]]]]
    expect(custom_flatten(list)).to eq([4,5,1,2,3,4,5,6,7,8,9])
  end
end

def custom_flatten(list)
  new_list = []

  list.each do |element|
    next if element.respond_to?(:empty?) && element.empty?

    if element.is_a?(Array)
      new_list += custom_flatten(element)
    else
      new_list << element
    end
  end

  new_list
end