1 files changed, 122 insertions, 0 deletions
diff --git a/spec/lib/gitlab/background_migration_spec.rb b/spec/lib/gitlab/background_migration_spec.rb
new file mode 100644
index 00000000000..4ad69aeba43
--- /dev/null
+++ b/spec/lib/gitlab/background_migration_spec.rb
@@ -0,0 +1,122 @@
+require 'spec_helper'
+
+describe Gitlab::BackgroundMigration do
+  describe '.queue' do
+    it 'returns background migration worker queue' do
+      expect(described_class.queue)
+        .to eq BackgroundMigrationWorker.sidekiq_options['queue']
+    end
+  end
+
+  describe '.steal' do
+    context 'when there are enqueued jobs present' do
+      let(:queue) do
+        [double(args: ['Foo', [10, 20]], queue: described_class.queue)]
+      end
+
+      before do
+        allow(Sidekiq::Queue).to receive(:new)
+          .with(described_class.queue)
+          .and_return(queue)
+      end
+
+      context 'when queue contains unprocessed jobs' do
+        it 'steals jobs from a queue' do
+          expect(queue[0]).to receive(:delete).and_return(true)
+
+          expect(described_class).to receive(:perform)
+            .with('Foo', [10, 20])
+
+          described_class.steal('Foo')
+        end
+
+        it 'does not steal job that has already been taken' do
+          expect(queue[0]).to receive(:delete).and_return(false)
+
+          expect(described_class).not_to receive(:perform)
+
+          described_class.steal('Foo')
+        end
+
+        it 'does not steal jobs for a different migration' do
+          expect(described_class).not_to receive(:perform)
+
+          expect(queue[0]).not_to receive(:delete)
+
+          described_class.steal('Bar')
+        end
+      end
+
+      context 'when one of the jobs raises an error' do
+        let(:migration) { spy(:migration) }
+
+        let(:queue) do
+          [double(args: ['Foo', [10, 20]], queue: described_class.queue),
+           double(args: ['Foo', [20, 30]], queue: described_class.queue)]
+        end
+
+        before do
+          stub_const("#{described_class}::Foo", migration)
+
+          allow(queue[0]).to receive(:delete).and_return(true)
+          allow(queue[1]).to receive(:delete).and_return(true)
+        end
+
+        it 'enqueues the migration again and re-raises the error' do
+          allow(migration).to receive(:perform).with(10, 20)
+            .and_raise(Exception, 'Migration error').once
+
+          expect(BackgroundMigrationWorker).to receive(:perform_async)
+            .with('Foo', [10, 20]).once
+
+          expect { described_class.steal('Foo') }.to raise_error(Exception)
+        end
+      end
+    end
+
+    context 'when there are scheduled jobs present', :sidekiq, :redis do
+      it 'steals all jobs from the scheduled sets' do
+        Sidekiq::Testing.disable! do
+          BackgroundMigrationWorker.perform_in(10.minutes, 'Object')
+
+          expect(Sidekiq::ScheduledSet.new).to be_one
+          expect(described_class).to receive(:perform).with('Object', any_args)
+
+          described_class.steal('Object')
+
+          expect(Sidekiq::ScheduledSet.new).to be_none
+        end
+      end
+    end
+
+    context 'when there are enqueued and scheduled jobs present', :sidekiq, :redis do
+      it 'steals from the scheduled sets queue first' do
+        Sidekiq::Testing.disable! do
+          expect(described_class).to receive(:perform)
+            .with('Object', [1]).ordered
+          expect(described_class).to receive(:perform)
+            .with('Object', [2]).ordered
+
+          BackgroundMigrationWorker.perform_async('Object', [2])
+          BackgroundMigrationWorker.perform_in(10.minutes, 'Object', [1])
+
+          described_class.steal('Object')
+        end
+      end
+    end
+  end
+
+  describe '.perform' do
+    let(:migration) { spy(:migration) }
+
+    before do
+      stub_const("#{described_class.name}::Foo", migration)
+    end
+
+    it 'performs a background migration' do
+      expect(migration).to receive(:perform).with(10, 20).once
+
+      described_class.perform('Foo', [10, 20])
+    end
+  end
+end