Pass demodulize class to BackgroundMigrationWorker

Since
https://gitlab.com/gitlab-org/gitlab/merge_requests/18048,
we no longer accept constants outside of
Gitlab::BackgroundMigration

Restore spec file with following changes:
- update schema: 2020_01_02_170221 to make spec work again
- Update spec for demodulized class name

ee/changelogs/unreleased/demodulize-backgroundmigration-pruneorphanedgeoevents.yml

+---
+title: Fix PruneOrphanedGeoEvents to pass in demodulized name to BackgroundMigrationWorker
+merge_request: 22451
+author:
+type: fixed

ee/lib/gitlab/background_migration/prune_orphaned_geo_events.rb

@@ -64,7 +64,7 @@ module Gitlab
         deleted_rows = prune_orphaned_rows(table_name)
         table_name   = next_table(table_name) if deleted_rows.zero?
 
-        BackgroundMigrationWorker.perform_in(RESCHEDULE_DELAY, self.class.name, table_name) if table_name
+        BackgroundMigrationWorker.perform_in(RESCHEDULE_DELAY, self.class.name.demodulize, table_name) if table_name
       end
 
       def prune_orphaned_rows(table)

ee/spec/lib/gitlab/background_migration/prune_orphaned_geo_events_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe Gitlab::BackgroundMigration::PruneOrphanedGeoEvents, :migration, :postgresql, geo: false, schema: 2020_01_02_170221 do
+  let(:event_table_name) { 'geo_repository_updated_events' }
+  let(:geo_event_log) { table(:geo_event_log) }
+  let(:geo_updated_events) { table(event_table_name) }
+  let(:namespace) { table(:namespaces).create(name: 'foo', path: 'foo') }
+  let(:project) { table(:projects).create(name: 'bar', path: 'path/to/bar', namespace_id: namespace.id) }
+
+  subject(:background_migration) { described_class.new }
+
+  describe 'PrunableEvent' do
+    subject(:prunable_event) do
+      Class.new(ActiveRecord::Base) do
+        include Gitlab::BackgroundMigration::PruneOrphanedGeoEvents::PrunableEvent
+
+        self.table_name = 'geo_repository_updated_events'
+      end
+    end
+
+    describe '.geo_event_foreign_key' do
+      it 'determines foreign key correctly' do
+        expect(subject.geo_event_foreign_key).to eq('repository_updated_event_id')
+      end
+    end
+
+    describe '.delete_batch_of_orphans!' do
+      it 'vacuums table after deleting rows' do
+        geo_updated_events.create!(project_id: project.id,
+                                   source: 0,
+                                   branches_affected: 0,
+                                   tags_affected: 0)
+
+        expect(subject).to receive(:vacuum!)
+
+        subject.delete_batch_of_orphans!
+      end
+    end
+  end
+
+  describe '#perform' do
+    before do
+      geo_updated_events.create!(project_id: project.id,
+                                 source: 0,
+                                 branches_affected: 0,
+                                 tags_affected: 0)
+    end
+
+    it 'does nothing if the database is read-only' do
+      allow(Gitlab::Database).to receive(:read_only?).and_return(true)
+
+      expect { background_migration.perform(event_table_name) }.not_to change { Geo::RepositoryUpdatedEvent.count }
+    end
+
+    it 'takes the first table if no table is specified' do
+      expect(subject).to receive(:prune_orphaned_rows).with(described_class::EVENT_TABLES.first).and_call_original
+
+      subject.perform
+    end
+
+    it 'deletes orphans' do
+      expect { background_migration.perform(event_table_name) }.to change { Geo::RepositoryUpdatedEvent.count }.by(-1)
+    end
+
+    it 'reschedules itself with the same table if positive number of rows were pruned' do
+      allow(subject).to receive(:prune_orphaned_rows).and_return(5)
+      expect(BackgroundMigrationWorker).to receive(:perform_in).with(5.minutes, described_class.name.demodulize, event_table_name)
+
+      subject.perform(event_table_name)
+    end
+
+    it 'reschedules itself with the next table if zero rows were pruned' do
+      allow(subject).to receive(:prune_orphaned_rows).and_return(0)
+      expect(BackgroundMigrationWorker).to receive(:perform_in).with(5.minutes, described_class.name.demodulize, 'geo_repository_deleted_events')
+
+      subject.perform(event_table_name)
+    end
+  end
+
+  describe '#prune_orphaned_rows' do
+    it 'returns the number of pruned rows' do
+      event_model = spy(:event_model)
+      allow(event_model).to receive(:delete_batch_of_orphans!).and_return(555)
+      allow(subject).to receive(:event_model).and_return(event_model)
+
+      expect(subject.prune_orphaned_rows(event_table_name)).to eq(555)
+    end
+  end
+
+  describe '#next_table' do
+    it 'takes the next table in the array' do
+      expect(subject.next_table(described_class::EVENT_TABLES.first)).to eq(described_class::EVENT_TABLES.second)
+    end
+
+    it 'stops with the last table' do
+      expect(subject.next_table(described_class::EVENT_TABLES.last)).to be_nil
+    end
+
+    it 'cycles for EVENT_TABLES.count' do
+      table_name = 'geo_repository_created_events'
+      count = 0
+
+      loop do
+        count += 1
+        table_name = subject.next_table(table_name)
+        break unless table_name
+      end
+
+      expect(count).to eq(described_class::EVENT_TABLES.count)
+    end
+  end
+end