def add_two(number = 0, *rest)
  return nil unless number.respond_to? :+

  # if number.respond_to? :+
    if number.respond_to? :concat
      puts "srsly?" if rest.size > 0
      if number.respond_to? :push
        number.push 2
      else
        number.concat "2"
      end
    else
      rest << number
      rest_sum = 0
      rest.each do |num|
        rest_sum += num
      end
      2 + rest_sum
    end
  # end
end

def add_five number
  # …
end

def test_add_two
  p add_two(2) == 4
  p add_two(1) == 3
  p add_two(1.0) == 3.0
  p add_two("a") == "a2"
  p add_two([]) == [2]
  p add_two([1]) == [1,2]
  p add_two({}) == nil
  p add_two(nil) == nil
  p add_two(true) == nil
  p add_two == 2
  p add_two(1,2) == 5
  p add_two("a", "b")
end

def test_add_five
  # test with expectation for add_five
end

def test_all
  test_add_two
  test_add_five
end

test_all