Add methods to check dead and retrying jobs

It adds two methods for checking if a background job
(for a given class) has dead or retrying jobs.

lib/gitlab/background_migration.rb

@@ -58,21 +58,37 @@ module Gitlab
       migration_class_for(class_name).new.perform(*arguments)
     end
 
-    def self.exists?(migration_class)
+    def self.exists?(migration_class, additional_queues = [])
       enqueued = Sidekiq::Queue.new(self.queue)
       scheduled = Sidekiq::ScheduledSet.new
 
-      [enqueued, scheduled].each do |queue|
-        queue.each do |job|
-          return true if job.queue == self.queue && job.args.first == migration_class
+      enqueued_job?([enqueued, scheduled], migration_class)
     end
+
+    def self.dead_jobs?(migration_class)
+      dead_set = Sidekiq::DeadSet.new
+
+      enqueued_job?([dead_set], migration_class)
     end
 
-      false
+    def self.retrying_jobs?(migration_class)
+      retry_set = Sidekiq::RetrySet.new
+
+      enqueued_job?([retry_set], migration_class)
     end
 
     def self.migration_class_for(class_name)
       const_get(class_name)
     end
+
+    def self.enqueued_job?(queues, migration_class)
+      queues.each do |queue|
+        queue.each do |job|
+          return true if job.queue == self.queue && job.args.first == migration_class
+        end
+      end
+
+      false
+    end
   end
 end

spec/lib/gitlab/background_migration_spec.rb

@@ -195,4 +195,44 @@ describe Gitlab::BackgroundMigration do
       end
     end
   end
+
+  describe '.dead_jobs?' do
+    let(:queue) do
+      [double(args: ['Foo', [10, 20]], queue: described_class.queue)]
+    end
+
+    context 'when there are dead jobs present' do
+      before do
+        allow(Sidekiq::DeadSet).to receive(:new).and_return(queue)
+      end
+
+      it 'returns true if specific job exists' do
+        expect(described_class.dead_jobs?('Foo')).to eq(true)
+      end
+
+      it 'returns false if specific job does not exist' do
+        expect(described_class.dead_jobs?('Bar')).to eq(false)
+      end
+    end
+  end
+
+  describe '.retrying_jobs?' do
+    let(:queue) do
+      [double(args: ['Foo', [10, 20]], queue: described_class.queue)]
+    end
+
+    context 'when there are dead jobs present' do
+      before do
+        allow(Sidekiq::RetrySet).to receive(:new).and_return(queue)
+      end
+
+      it 'returns true if specific job exists' do
+        expect(described_class.retrying_jobs?('Foo')).to eq(true)
+      end
+
+      it 'returns false if specific job does not exist' do
+        expect(described_class.retrying_jobs?('Bar')).to eq(false)
+      end
+    end
+  end
 end