Function that rearranges an array of positive integers to produce largest possible integer when concatenated

special_sort.rb

# === Program

class Main
  def compare(n1, n2)
    (n1 + n2).to_i > (n2 + n1).to_i
  end

  def special_sort(arr)
    result = []
    temp = []

    arr.each do |el|
      el = el.to_s

      while result.length > 0 && compare(el, result[-1])
        temp.push(result.pop)
      end
      result.push(el)

      while temp.length > 0
        result.push(temp.pop)
      end
    end

    result.join.to_i
  end
end

# === Unit Tests

require 'minitest/autorun'
require 'minitest/reporters'
Minitest::Reporters.use! Minitest::Reporters::SpecReporter.new

class TestMain < Minitest::Test
  def setup
    @main = Main.new
    @data = [
        { arr: [47, 2, 3, 8], ans: 84732 },
        { arr: [47, 40, 4], ans: 47440 },
        { arr: [42, 40, 4], ans: 44240 },
        { arr: [421, 42, 423], ans: 42423421 },
        { arr: [47, 2, 3, 8, 47, 40, 4, 42, 40, 4, 421, 42, 423], ans: 84747444242423421404032 }
      ]
  end

  def test_compare
    assert_equal false, @main.compare("421", "42")
    assert_equal true , @main.compare("42", "421")
  end

  def test_special_sort
    @data.each do |el|
      assert_equal el[:ans], @main.special_sort(el[:arr])
    end
  end
end