stack_machine.rb

require 'minitest/autorun'
require 'byebug'

def stack_machine(string)
  result = []
  numbers = []

  string.split.each do |token|
    if /(\d)/.match(token)
      numbers << Integer(token)
    else
      result << numbers.reduce(&token.to_sym)
      numbers.clear
    end
  end
  result
end


class StackMachineTest < MiniTest::Test

  def test_addition
    assert_equal [3, 6, 8], stack_machine('1 2 + 3 3 + 4 4 +')
  end

  def test_multiplication
    assert_equal [9, 12, 28], stack_machine('3 3 * 3 4 * 7 4 *')
  end

  def test_division
    assert_equal [4, 3, 2], stack_machine('8 2 / 9 3 / 148 74 /')
  end

  def test_subtraction
    assert_equal [99, 567, 5], stack_machine('100 1 - 965 398 - 15 10 -')
  end

  def test_multiple_arguments
    assert_equal [3, 6, 99], stack_machine('1 1 1 + 3 2 * 199 50 50 -')
  end

end