Whale question

whale_test.rb

require 'test/unit'

class Whale
  def self.attr_validated(method_name, &validation)
    # Enter code here to make all tests pass.
  end

  attr_validated :num_teeth do |v|
    v <= 4
  end
end

class TestWhale < Test::Unit::TestCase
  def test_good_value
    whale = Whale.new
    whale.num_teeth = 3

    assert_equal 3, whale.num_teeth
  end

  def test_nil_value
    whale = Whale.new
    assert_raises ArgumentError do
      whale.num_teeth = nil
    end
  end

  def test_illegal_value
    whale = Whale.new
    assert_raises ArgumentError do
      whale.num_teeth = 5
    end
  end
end