1 files changed, 52 insertions, 0 deletions
diff --git a/spec/models/preloaders/labels_preloader_spec.rb b/spec/models/preloaders/labels_preloader_spec.rb
new file mode 100644
index 00000000000..94de00bb94c
--- /dev/null
+++ b/spec/models/preloaders/labels_preloader_spec.rb
@@ -0,0 +1,52 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Preloaders::LabelsPreloader do
+  let_it_be(:user) { create(:user) }
+
+  shared_examples 'an efficient database query' do
+    let(:subscriptions) { labels.each { |l| create(:subscription, subscribable: l, project: l.project, user: user) }}
+
+    it 'does not make n+1 queries' do
+      first_label = labels_with_preloaded_data.first
+      clean_labels = labels_with_preloaded_data
+
+      expect { access_data(clean_labels) }.to issue_same_number_of_queries_as { access_data([first_label]) }
+    end
+  end
+
+  context 'project labels' do
+    let_it_be(:projects) { create_list(:project, 3, :public, :repository) }
+    let_it_be(:labels) { projects.each { |p| create(:label, project: p) } }
+
+    it_behaves_like 'an efficient database query'
+  end
+
+  context 'group labels' do
+    let_it_be(:groups) { create_list(:group, 3) }
+    let_it_be(:labels) { groups.each { |g| create(:group_label, group: g) } }
+
+    it_behaves_like 'an efficient database query'
+  end
+
+  private
+
+  def labels_with_preloaded_data
+    l = Label.where(id: labels.map(&:id))
+    described_class.new(l, user).preload_all
+    l
+  end
+
+  def access_data(labels)
+    labels.each do |label|
+      if label.is_a?(ProjectLabel)
+        label.project.project_feature
+        label.lazy_subscription(user, label.project)
+      elsif label.is_a?(GroupLabel)
+        label.group.route
+        label.lazy_subscription(user)
+      end
+    end
+  end
+end