Integer to Roman Number string conversion (kata, exercise)

roman_num.rb

class Roman
  NUMS = [
    [10, 'X'],
    [9, 'IX'],
    [5, 'V'],
    [4, 'IV'],
    [1, 'I']
  ].freeze

  def self.from(val)
    new(val.to_i)
  end

  def initialize(int)
    @value = NUMS.reduce('') do |acc, (num, roman)|
      while int >= num
        acc += roman
        int -= num
      end
      acc
    end
  end

  def to_s
    @value
  end
end

RSpec.describe Roman do
  it 'should convert 1 number to I' do
    expect(Roman.from(1).to_s).to eq('I')
  end

  it 'should convert 2 number to II' do
    expect(Roman.from(2).to_s).to eq('II')
  end

  it 'should convert 4 number to IV' do
    expect(Roman.from(4).to_s).to eq('IV')
  end

  it 'should convert 7 number to VII' do
    expect(Roman.from(7).to_s).to eq('VII')
  end

  it 'should convert 9 number to VII' do
    expect(Roman.from(9).to_s).to eq('IX')
  end

  it 'should convert 10 number to X' do
    expect(Roman.from(10).to_s).to eq('X')
  end

  it 'should convert 13 number to XIII' do
    expect(Roman.from(13).to_s).to eq('XIII')
  end

  it 'should convert 26 number to XXVI' do
    expect(Roman.from(26).to_s).to eq('XXVI')
  end

  it 'should convert 39 number to XXXIX' do
    expect(Roman.from(39).to_s).to eq('XXXIX')
  end
end