reverse.rb

gem 'minitest', '>= 5.0.0'
require 'minitest/autorun'

def reverse(string)
  result = ""
  string.length.times do |i|
    result = string[i] + result
  end
  result
end

class TestRev < Minitest::Test
  def test_reverse
    assert_equal "evissam", reverse("massive")
  end
end