1 files changed, 42 insertions, 0 deletions
diff --git a/spec/models/preloaders/merge_requests_preloader_spec.rb b/spec/models/preloaders/merge_requests_preloader_spec.rb
new file mode 100644
index 00000000000..7108de2e491
--- /dev/null
+++ b/spec/models/preloaders/merge_requests_preloader_spec.rb
@@ -0,0 +1,42 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Preloaders::MergeRequestsPreloader do
+  describe '#execute' do
+    let_it_be_with_refind(:merge_requests) { create_list(:merge_request, 3) }
+    let_it_be(:upvotes) { merge_requests.each { |m| create(:award_emoji, :upvote, awardable: m) } }
+
+    it 'does not make n+1 queries' do
+      described_class.new(merge_requests).execute
+
+      control = ActiveRecord::QueryRecorder.new(skip_cached: false) do
+        # expectations make sure the queries execute
+        merge_requests.each do |m|
+          expect(m.target_project.project_feature).not_to be_nil
+          expect(m.lazy_upvotes_count).to eq(1)
+        end
+      end
+
+      # 1 query for BatchLoader to load all upvotes at once
+      expect(control.count).to eq(1)
+    end
+
+    it 'runs extra queries without preloading' do
+      control = ActiveRecord::QueryRecorder.new(skip_cached: false) do
+        # expectations make sure the queries execute
+        merge_requests.each do |m|
+          expect(m.target_project.project_feature).not_to be_nil
+          expect(m.lazy_upvotes_count).to eq(1)
+        end
+      end
+
+      # 4 queries per merge request =
+      # 1 to load merge request
+      # 1 to load project
+      # 1 to load project_feature
+      # 1 to load upvotes count
+      expect(control.count).to eq(4 * merge_requests.size)
+    end
+  end
+end