Use average of coverage values to avoid upsert error

Given we use the build's group_name there are chances that
in some projects, each build group will still store its own
coverage. This would cause SQL errors when upserting because
it will violate the constraint when we try to upsert multiple
instances of the same group name.

app/services/ci/daily_report_result_service.rb

@@ -19,12 +19,21 @@ module Ci
         last_pipeline_id: pipeline.id
       }
 
-      pipeline.builds.with_coverage.map do |build|
+      aggregate(pipeline.builds.with_coverage).map do |group_name, group|
         base_attrs.merge(
-          title: build.group_name,
-          value: build.coverage
+          title: group_name,
+          value: average_coverage(group)
         )
       end
     end
+
+    def aggregate(builds)
+      builds.group_by(&:group_name)
+    end
+
+    def average_coverage(group)
+      total_coverage = group.reduce(0.0) { |sum, build| sum + build.coverage }
+      (total_coverage / group.size).round(2)
+    end
   end
 end

changelogs/unreleased/eb-fix-daily-report-results-upsert.yml

+---
+title: Fix daily report result to use average of coverage values if there are multiple builds for a given group
+  name
+merge_request: 28556
+author:
+type: fixed

spec/services/ci/daily_report_result_service_spec.rb

@@ -38,6 +38,27 @@ describe Ci::DailyReportResultService, '#execute' do
     expect(Ci::DailyReportResult.find_by(title: 'extra')).to be_nil
   end
 
+  context 'when there are multiple builds with the same group name that report coverage' do
+    let!(:test_job_1) { create(:ci_build, pipeline: pipeline, name: '1/2 test', coverage: 70) }
+    let!(:test_job_2) { create(:ci_build, pipeline: pipeline, name: '2/2 test', coverage: 80) }
+
+    it 'creates daily code coverage record with the average as the value' do
+      described_class.new.execute(pipeline)
+
+      Ci::DailyReportResult.find_by(title: 'test').tap do |coverage|
+        expect(coverage).to have_attributes(
+          project_id: pipeline.project.id,
+          last_pipeline_id: pipeline.id,
+          ref_path: pipeline.source_ref_path,
+          param_type: 'coverage',
+          title: test_job_2.group_name,
+          value: 75,
+          date: pipeline.created_at.to_date
+        )
+      end
+    end
+  end
+
   context 'when there is an existing daily code coverage for the matching date, project, ref_path, and group name' do
     let!(:new_pipeline) do
       create(