如何测试 Rails 缓存功能

问题描述

这是我的标签模型，我不知道如何测试 Rails.cache 功能.

This is my Tag model and I don't know how can I test Rails.cache feature.

class Tag < ActiveRecord::Base
  class << self
    def all_cached
      Rails.cache.fetch("tags.all", :expires_in => 3.hours) do
        Tag.order('name asc').to_a
      end
    end
    def find_cached(id)
      Rails.cache.fetch("tags/#{id}", :expires_in => 3.hours) do
        Tag.find(id)
      end
    end
  end

  attr_accessible :name
  has_friendly_id :name, :use_slug => true, :approximate_ascii => true
  has_many :taggings #, :dependent => :destroy
  has_many :projects, :through => :taggings
end

你知道如何进行测试吗?

Do you know how can it will be tested ?

推荐答案

首先，您不应该真正测试框架.Rails 的缓存测试表面上为您涵盖了这一点.也就是说，请参阅这个答案，您可以从中获得一些帮助利用.您的测试将如下所示:

Well, first, you shouldn't really be testing the framework. Rails' caching tests ostensibly cover that for you. That said, see this answer for a little helper you can use. Your tests would then look something like:

describe Tag do
  describe "::all_cached" do
    around {|ex| with_caching { ex.run } }
    before { Rails.cache.clear }

    context "given that the cache is unpopulated" do
      it "does a database lookup" do
        Tag.should_receive(:order).once.and_return(["tag"])
        Tag.all_cached.should == ["tag"]
      end
    end

    context "given that the cache is populated" do
      let!(:first_hit) { Tag.all_cached }

      it "does a cache lookup" do
        before do
          Tag.should_not_receive(:order)
          Tag.all_cached.should == first_hit
        end
      end
    end
  end
end

这实际上并不检查缓存机制——只是没有调用 #fetch 块.它很脆弱，并且与 fetch 块的实现相关联，所以要小心，因为它会成为维护债务.

This doesn't actually check the caching mechanism - just that the #fetch block isn't invoked. It's brittle and tied to the implementation of the fetch block, so beware that as it will become maintenance debt.

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