Smallets Positive Integer

smallest.rb

class Smallest
  def self.resolve(array_size, array_of_numbers)
    ( (1..array_size + 1).to_a - array_of_numbers ).min
  end
end

smallest_test.rb

require 'test/unit'
require_relative './smallest'

class SmallestTest < Test::Unit::TestCase
  def test_4
    assert_equal 4, Smallest.resolve(3, [1, 2, 3])
  end

  def test_2
    assert_equal 2, Smallest.resolve(3, [5, 3, 1])
  end

  def test_1
    assert_equal 1, Smallest.resolve(5, [2, 3, 4, 5, -10])
  end
end