Add tests to the Feed model (#2594)

This adds a test for the `Feed#get` method. While the data
transformations in `Feed#get` may seem redundant, they are important to
maintain the order from Redis. The tests I wrote will fail if someone
tries to refactor away this "redundancy" (as I tried to do in the first
iteration of this change).

spec/models/feed_spec.rb

@@ -2,6 +2,20 @@ require 'rails_helper'
 
 RSpec.describe Feed, type: :model do
   describe '#get' do
-    pending
+    it "gets statuses with ids in the range, maintining the order from Redis" do
+      account = Fabricate(:account)
+      Fabricate(:status, account: account, id: 1)
+      Fabricate(:status, account: account, id: 2)
+      Fabricate(:status, account: account, id: 3)
+      Fabricate(:status, account: account, id: 10)
+      redis = double(zrevrangebyscore: [["val2", 2.0], ["val1", 1.0], ["val3", 3.0], ["deleted", 4.0]])
+      allow(Redis).to receive(:current).and_return(redis)
+
+      feed = Feed.new("type", account)
+      results = feed.get(3)
+
+      expect(results.map(&:id)).to eq [2, 1, 3]
+      expect(results.first.attributes.keys).to eq ["id", "updated_at"]
+    end
   end
 end