Remove tests_total_count from PipelineEntity

This MR stops exposing tests_total_count data from our
PipelineEntity as we don't use it in our frontend.
It also starts memoizing test_report_summary.

Apply code review feedback

app/models/ci/pipeline.rb

@@ -869,7 +869,9 @@ module Ci
     end
 
     def test_report_summary
-      Gitlab::Ci::Reports::TestReportSummary.new(latest_builds_report_results)
+      strong_memoize(:test_report_summary) do
+        Gitlab::Ci::Reports::TestReportSummary.new(latest_builds_report_results)
+      end
     end
 
     def test_reports

app/serializers/pipeline_entity.rb

@@ -85,10 +85,6 @@ class PipelineEntity < Grape::Entity
     pipeline.failed_builds
   end
 
-  expose :tests_total_count do |pipeline|
-    pipeline.test_report_summary.total[:count]
-  end
-
   private
 
   alias_method :pipeline, :object

spec/controllers/projects/pipelines_controller_spec.rb

@@ -43,7 +43,7 @@ RSpec.describe Projects::PipelinesController do
         end
       end
 
-      it 'executes N+1 queries' do
+      it 'does not execute N+1 queries' do
         get_pipelines_index_json
 
         control_count = ActiveRecord::QueryRecorder.new do
@@ -53,7 +53,7 @@ RSpec.describe Projects::PipelinesController do
         create_all_pipeline_types
 
         # There appears to be one extra query for Pipelines#has_warnings? for some reason
-        expect { get_pipelines_index_json }.not_to exceed_query_limit(control_count + 7)
+        expect { get_pipelines_index_json }.not_to exceed_query_limit(control_count + 1)
         expect(response).to have_gitlab_http_status(:ok)
         expect(json_response['pipelines'].count).to eq 12
       end

spec/serializers/pipeline_entity_spec.rb

@@ -260,13 +260,5 @@ RSpec.describe PipelineEntity do
         end
       end
     end
-
-    context 'when pipeline has build report results' do
-      let(:pipeline) { create(:ci_pipeline, :with_report_results, project: project, user: user) }
-
-      it 'exposes tests total count' do
-        expect(subject[:tests_total_count]).to eq(2)
-      end
-    end
   end
 end

spec/serializers/pipeline_serializer_spec.rb

@@ -155,7 +155,7 @@ RSpec.describe PipelineSerializer do
 
         it 'verifies number of queries', :request_store do
           recorded = ActiveRecord::QueryRecorder.new { subject }
-          expected_queries = Gitlab.ee? ? 46 : 43
+          expected_queries = Gitlab.ee? ? 43 : 40
 
           expect(recorded.count).to be_within(2).of(expected_queries)
           expect(recorded.cached_count).to eq(0)