Add specs for pipeline sidekiq queues migration

spec/migrations/migrate_pipeline_sidekiq_queues_spec.rb

+require 'spec_helper'
+require Rails.root.join('db', 'post_migrate', '20170822101017_migrate_pipeline_sidekiq_queues.rb')
+
+describe MigratePipelineSidekiqQueues, :sidekiq, :redis do
+  include Gitlab::Database::MigrationHelpers
+
+  context 'when there are jobs in the queues' do
+    it 'correctly migrates queue when migrating up' do
+      Sidekiq::Testing.disable! do
+        stubbed_worker(queue: :pipeline).perform_async('Something', [1])
+        stubbed_worker(queue: :build).perform_async('Something', [1])
+
+        described_class.new.up
+
+        expect(sidekiq_queue_length('pipeline')).to eq 0
+        expect(sidekiq_queue_length('build')).to eq 0
+        expect(sidekiq_queue_length('pipeline_default')).to eq 2
+      end
+    end
+
+    it 'correctly migrates queue when migrating down' do
+      Sidekiq::Testing.disable! do
+        stubbed_worker(queue: :pipeline_default).perform_async('Class', [1])
+        stubbed_worker(queue: :pipeline_default).perform_async('Class', [2])
+
+        described_class.new.down
+
+        expect(sidekiq_queue_length('pipeline')).to eq 2
+        expect(sidekiq_queue_length('pipeline_default')).to eq 0
+      end
+    end
+  end
+
+  context 'when there are no jobs in the queues' do
+    it 'does not raise error when migrating up' do
+      expect { described_class.new.up }.not_to raise_error
+    end
+
+    it 'does not raise error when migrating down' do
+      expect { described_class.new.down }.not_to raise_error
+    end
+  end
+
+  def stubbed_worker(queue:)
+    Class.new do
+      include Sidekiq::Worker
+      sidekiq_options queue: queue
+    end
+  end
+end