3 files changed, 134 insertions, 0 deletions
diff --git a/spec/models/preloaders/commit_status_preloader_spec.rb b/spec/models/preloaders/commit_status_preloader_spec.rb
new file mode 100644
index 00000000000..85ea784335c
--- /dev/null
+++ b/spec/models/preloaders/commit_status_preloader_spec.rb
@@ -0,0 +1,41 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Preloaders::CommitStatusPreloader do
+  let_it_be(:pipeline) { create(:ci_pipeline) }
+
+  let_it_be(:build1) { create(:ci_build, :tags, pipeline: pipeline) }
+  let_it_be(:build2) { create(:ci_build, :tags, pipeline: pipeline) }
+  let_it_be(:bridge1) { create(:ci_bridge, pipeline: pipeline) }
+  let_it_be(:bridge2) { create(:ci_bridge, pipeline: pipeline) }
+  let_it_be(:generic_commit_status1) { create(:generic_commit_status, pipeline: pipeline) }
+  let_it_be(:generic_commit_status2) { create(:generic_commit_status, pipeline: pipeline) }
+
+  describe '#execute' do
+    let(:relations) { %i[pipeline metadata tags job_artifacts_archive downstream_pipeline] }
+    let(:statuses) { CommitStatus.where(commit_id: pipeline.id).all }
+
+    subject(:execute) { described_class.new(statuses).execute(relations) }
+
+    it 'prevents N+1 for specified relations', :use_sql_query_cache do
+      execute
+
+      control_count = ActiveRecord::QueryRecorder.new(skip_cached: false) do
+        call_each_relation(statuses.sample(3))
+      end
+
+      expect do
+        call_each_relation(statuses)
+      end.to issue_same_number_of_queries_as(control_count)
+    end
+
+    private
+
+    def call_each_relation(statuses)
+      statuses.each do |status|
+        relations.each { |relation| status.public_send(relation) if status.respond_to?(relation) }
+      end
+    end
+  end
+end
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
diff --git a/spec/models/preloaders/user_max_access_level_in_groups_preloader_spec.rb b/spec/models/preloaders/user_max_access_level_in_groups_preloader_spec.rb
new file mode 100644
index 00000000000..8144e1ad233
--- /dev/null
+++ b/spec/models/preloaders/user_max_access_level_in_groups_preloader_spec.rb
@@ -0,0 +1,51 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Preloaders::UserMaxAccessLevelInGroupsPreloader do
+  let_it_be(:user) { create(:user) }
+  let_it_be(:group1) { create(:group, :private).tap { |g| g.add_developer(user) } }
+  let_it_be(:group2) { create(:group, :private).tap { |g| g.add_developer(user) } }
+  let_it_be(:group3) { create(:group, :private) }
+
+  let(:max_query_regex) { /SELECT MAX\("members"\."access_level"\).+/ }
+  let(:groups) { [group1, group2, group3] }
+
+  shared_examples 'executes N max member permission queries to the DB' do
+    it 'executes the specified max membership queries' do
+      queries = ActiveRecord::QueryRecorder.new do
+        groups.each { |group| user.can?(:read_group, group) }
+      end
+
+      max_queries = queries.log.grep(max_query_regex)
+
+      expect(max_queries.count).to eq(expected_query_count)
+    end
+  end
+
+  context 'when the preloader is used', :request_store do
+    before do
+      described_class.new(groups, user).execute
+    end
+
+    it_behaves_like 'executes N max member permission queries to the DB' do
+      # Will query all groups where the user is not already a member
+      let(:expected_query_count) { 1 }
+    end
+
+    context 'when user has access but is not a direct member of the group' do
+      let(:groups) { [group1, group2, group3, create(:group, :private, parent: group1)] }
+
+      it_behaves_like 'executes N max member permission queries to the DB' do
+        # One query for group with no access and another one where the user is not a direct member
+        let(:expected_query_count) { 2 }
+      end
+    end
+  end
+
+  context 'when the preloader is not used', :request_store do
+    it_behaves_like 'executes N max member permission queries to the DB' do
+      let(:expected_query_count) { groups.count }
+    end
+  end
+end