1 files changed, 182 insertions, 0 deletions
diff --git a/spec/lib/gitlab/database/background_migration/scheduler_spec.rb b/spec/lib/gitlab/database/background_migration/scheduler_spec.rb
new file mode 100644
index 00000000000..ba745acdf8a
--- /dev/null
+++ b/spec/lib/gitlab/database/background_migration/scheduler_spec.rb
@@ -0,0 +1,182 @@
+# frozen_string_literal: true
+
+require 'spec_helper'
+
+RSpec.describe Gitlab::Database::BackgroundMigration::Scheduler, '#perform' do
+  let(:scheduler) { described_class.new }
+
+  shared_examples_for 'it has no jobs to run' do
+    it 'does not create and run a migration job' do
+      test_wrapper = double('test wrapper')
+
+      expect(test_wrapper).not_to receive(:perform)
+
+      expect do
+        scheduler.perform(migration_wrapper: test_wrapper)
+      end.not_to change { Gitlab::Database::BackgroundMigration::BatchedJob.count }
+    end
+  end
+
+  context 'when there are no active migrations' do
+    let!(:migration) { create(:batched_background_migration, :finished) }
+
+    it_behaves_like 'it has no jobs to run'
+  end
+
+  shared_examples_for 'it has completed the migration' do
+    it 'marks the migration as finished' do
+      relation = Gitlab::Database::BackgroundMigration::BatchedMigration.finished.where(id: first_migration.id)
+
+      expect { scheduler.perform }.to change { relation.count }.by(1)
+    end
+  end
+
+  context 'when there are active migrations' do
+    let!(:first_migration) { create(:batched_background_migration, :active, batch_size: 2) }
+    let!(:last_migration) { create(:batched_background_migration, :active) }
+
+    let(:job_relation) do
+      Gitlab::Database::BackgroundMigration::BatchedJob.where(batched_background_migration_id: first_migration.id)
+    end
+
+    context 'when the migration interval has not elapsed' do
+      before do
+        expect_next_found_instance_of(Gitlab::Database::BackgroundMigration::BatchedMigration) do |migration|
+          expect(migration).to receive(:interval_elapsed?).and_return(false)
+        end
+      end
+
+      it_behaves_like 'it has no jobs to run'
+    end
+
+    context 'when the interval has elapsed' do
+      before do
+        expect_next_found_instance_of(Gitlab::Database::BackgroundMigration::BatchedMigration) do |migration|
+          expect(migration).to receive(:interval_elapsed?).and_return(true)
+        end
+      end
+
+      context 'when the first migration has no previous jobs' do
+        context 'when the migration has batches to process' do
+          let!(:event1) { create(:event) }
+          let!(:event2) { create(:event) }
+          let!(:event3) { create(:event) }
+
+          it 'runs the job for the first batch' do
+            first_migration.update!(min_value: event1.id, max_value: event3.id)
+
+            expect_next_instance_of(Gitlab::Database::BackgroundMigration::BatchedMigrationWrapper) do |wrapper|
+              expect(wrapper).to receive(:perform).and_wrap_original do |_, job_record|
+                expect(job_record).to eq(job_relation.first)
+              end
+            end
+
+            expect { scheduler.perform }.to change { job_relation.count }.by(1)
+
+            expect(job_relation.first).to have_attributes(
+              min_value: event1.id,
+              max_value: event2.id,
+              batch_size: first_migration.batch_size,
+              sub_batch_size: first_migration.sub_batch_size)
+          end
+        end
+
+        context 'when the migration has no batches to process' do
+          it_behaves_like 'it has no jobs to run'
+          it_behaves_like 'it has completed the migration'
+        end
+      end
+
+      context 'when the first migration has previous jobs' do
+        let!(:event1) { create(:event) }
+        let!(:event2) { create(:event) }
+        let!(:event3) { create(:event) }
+
+        let!(:previous_job) do
+          create(:batched_background_migration_job,
+            batched_migration: first_migration,
+            min_value: event1.id,
+            max_value: event2.id,
+            batch_size: 2,
+            sub_batch_size: 1)
+        end
+
+        context 'when the migration is ready to process another job' do
+          it 'runs the migration job for the next batch' do
+            first_migration.update!(min_value: event1.id, max_value: event3.id)
+
+            expect_next_instance_of(Gitlab::Database::BackgroundMigration::BatchedMigrationWrapper) do |wrapper|
+              expect(wrapper).to receive(:perform).and_wrap_original do |_, job_record|
+                expect(job_record).to eq(job_relation.last)
+              end
+            end
+
+            expect { scheduler.perform }.to change { job_relation.count }.by(1)
+
+            expect(job_relation.last).to have_attributes(
+              min_value: event3.id,
+              max_value: event3.id,
+              batch_size: first_migration.batch_size,
+              sub_batch_size: first_migration.sub_batch_size)
+          end
+        end
+
+        context 'when the migration has no batches remaining' do
+          let!(:final_job) do
+            create(:batched_background_migration_job,
+              batched_migration: first_migration,
+              min_value: event3.id,
+              max_value: event3.id,
+              batch_size: 2,
+              sub_batch_size: 1)
+          end
+
+          it_behaves_like 'it has no jobs to run'
+          it_behaves_like 'it has completed the migration'
+        end
+      end
+
+      context 'when the bounds of the next batch exceed the migration maximum value' do
+        let!(:events) { create_list(:event, 3) }
+        let(:event1) { events[0] }
+        let(:event2) { events[1] }
+
+        context 'when the batch maximum exceeds the migration maximum' do
+          it 'clamps the batch maximum to the migration maximum' do
+            first_migration.update!(batch_size: 5, min_value: event1.id, max_value: event2.id)
+
+            expect_next_instance_of(Gitlab::Database::BackgroundMigration::BatchedMigrationWrapper) do |wrapper|
+              expect(wrapper).to receive(:perform)
+            end
+
+            expect { scheduler.perform }.to change { job_relation.count }.by(1)
+
+            expect(job_relation.first).to have_attributes(
+              min_value: event1.id,
+              max_value: event2.id,
+              batch_size: first_migration.batch_size,
+              sub_batch_size: first_migration.sub_batch_size)
+          end
+        end
+
+        context 'when the batch minimum exceeds the migration maximum' do
+          let!(:previous_job) do
+            create(:batched_background_migration_job,
+              batched_migration: first_migration,
+              min_value: event1.id,
+              max_value: event2.id,
+              batch_size: 5,
+              sub_batch_size: 1)
+          end
+
+          before do
+            first_migration.update!(batch_size: 5, min_value: 1, max_value: event2.id)
+          end
+
+          it_behaves_like 'it has no jobs to run'
+          it_behaves_like 'it has completed the migration'
+        end
+      end
+    end
+  end
+end