如何清除ruby中rspec测试之间的类变量

我有以下类：
我想确保类url只为所有实例设置一次。

I have the following class: I want to ensure the class url is only set once for all instances.

class DataFactory
  @@url = nil

  def initialize()
begin
    if @@url.nil?
       Rails.logger.debug "Setting url"
       @@url = MY_CONFIG["my value"]
    end
rescue Exception
  raise DataFactoryError, "Error!"
end
  end
end

我有两个测试： / p>

I have two tests:

it "should log a message" do
  APP_CONFIG = {"my value" => "test"}
  Rails.stub(:logger).and_return(logger_mock)
  logger_mock.should_receive(:debug).with "Setting url"

  t = DataFactory.new
  t = nil
end

it "should throw an exception" do
  APP_CONFIG = nil

  expect {
    DataFactory.new
  }.to raise_error(DataFactoryError, /Error!/)
end

问题是第二个测试永远不会抛出异常，因为@@ url类变量仍然设置从第一个测试第二个测试运行时。
虽然我在第一个测试的结尾处有nil实例垃圾回收在第二个测试运行之前没有清除内存：

The problem is the second test never throws an exception as the @@url class variable is still set from the first test when the second test runs. Even though I have se the instance to nil at the end of the first test garbage collection has not cleared the memory before the second test runs:

任何想法会很好！
我听说你可能使用Class.new，但我不知道该怎么做。

Any ideas would be great! I did hear you could possibly use Class.new but I am not sure how to go about this.