Recursive Letters with Indentations

recursive_letters.rb

def recursive_letters(letters, depth = 0)
  character = letters.shift
  indentation = '  ' * depth
  puts "#{indentation}<#{character}>"
  recursive_letters(letters, depth + 1) unless letters.empty?
  puts "#{indentation}</#{character}>"
end

recursive_letters_spec.rb

require 'rspec'
require './recursive_letters'

describe :recursive_letters do
  subject { recursive_letters %w[a b c d e f] }

  expected_output = <<~OUTPUT
    <a>
      <b>
        <c>
          <d>
            <e>
              <f>
              </f>
            </e>
          </d>
        </c>
      </b>
    </a>
  OUTPUT

  it 'outputs the expected output' do
    expect { subject }.to output(expected_output).to_stdout
  end
end