CODEWITHSUNDEEP
ruby-on-railscachingrspec
Johnny Cash
Johnny Cash

Reputation: 5147

how can I test rails cache feature

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

Do you know how can it will be tested ?

Upvotes: 8

Views: 19907

Answers (2)

Hirurg103
Hirurg103

Reputation: 4953

I agree with @chris-heald's answer. To make tests less brittle you could change your code this way:

def self.all_cached
  Rails.cache.fetch('tags.all', expires_in: 3.hours) do
    all_uncached
  end
end

def self.all_uncached
  Tag.order('name asc').to_a
end

and test it the following way:

describe Tag do
  context 'retrieving all tags' do
    let(:tag) { Tag.create! }
    before do
      allow(Tag).to receive(:all_uncached) do
        fail 'Database hit!' if @database_hit
        @database_hit = true
        [tag]
      end
    end

    context 'when the cache is populated' do
      before { Tag.all_cached }

      it 'should not hit the database' do
        expect(Tag.all_uncached).to raise_error 'Database hit!'
        expect(Tag.all_cached).to eq [tag]
      end
    end
  end
end

Upvotes: 0

Chris Heald
Chris Heald

Reputation: 62658

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

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.

Upvotes: 8

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