Fix existing_errors for AccessibilityReportsComparer

This commit fixes how we calculate our existing_errors between
2 accessibility reports. Instead of returning all existing errors
from the base report we are now getting the intersection between
the base and the head report.

lib/gitlab/ci/reports/accessibility_reports_comparer.rb

@@ -9,46 +9,44 @@ module Gitlab
         STATUS_SUCCESS = 'success'
         STATUS_FAILED = 'failed'
 
-        attr_reader :base_reports, :head_reports
+        attr_reader :base_report, :head_report
 
-        def initialize(base_reports, head_reports)
-          @base_reports = base_reports || AccessibilityReports.new
-          @head_reports = head_reports
+        def initialize(base_report, head_report)
+          @base_report = base_report || AccessibilityReports.new
+          @head_report = head_report
         end
 
         def status
-          head_reports.errors_count > 0 ? STATUS_FAILED : STATUS_SUCCESS
+          head_report.errors_count > 0 ? STATUS_FAILED : STATUS_SUCCESS
         end
 
         def existing_errors
           strong_memoize(:existing_errors) do
-            base_reports.all_errors
+            base_report.all_errors & head_report.all_errors
           end
         end
 
         def new_errors
           strong_memoize(:new_errors) do
-            head_reports.all_errors - base_reports.all_errors
+            head_report.all_errors - base_report.all_errors
           end
         end
 
         def resolved_errors
           strong_memoize(:resolved_errors) do
-            base_reports.all_errors - head_reports.all_errors
+            base_report.all_errors - head_report.all_errors
           end
         end
 
-        def errors_count
-          head_reports.errors_count
-        end
-
         def resolved_count
           resolved_errors.size
         end
 
         def total_count
-          existing_errors.size + new_errors.size
+          head_report.errors_count
         end
+
+        alias_method :errors_count, :total_count
       end
     end
   end

spec/serializers/accessibility_reports_comparer_entity_spec.rb

@@ -51,8 +51,8 @@ RSpec.describe AccessibilityReportsComparerEntity do
         expect(subject[:status]).to eq(Gitlab::Ci::Reports::AccessibilityReportsComparer::STATUS_FAILED)
         expect(subject[:resolved_errors].first).to include(:code, :type, :type_code, :message, :context, :selector, :runner, :runner_extras)
         expect(subject[:new_errors].first).to include(:code, :type, :type_code, :message, :context, :selector, :runner, :runner_extras)
-        expect(subject[:existing_errors].first).to include(:code, :type, :type_code, :message, :context, :selector, :runner, :runner_extras)
-        expect(subject[:summary]).to include(total: 2, resolved: 1, errored: 1)
+        expect(subject[:existing_errors]).to be_empty
+        expect(subject[:summary]).to include(total: 1, resolved: 1, errored: 1)
       end
     end