Add specs checking keeping milestones

spec/support/shared_examples/services/boards/issues_move_service.rb

@@ -39,6 +39,22 @@ shared_examples 'issues move service' do |group|
     end
   end
 
+  context 'when moving to backlog' do
+    let(:milestone) { create(:milestone, project: project) }
+    let!(:backlog)  { create(:backlog_list, board: board1) }
+
+    let(:issue)  { create(:labeled_issue, project: project, labels: [bug, development, testing, regression], milestone: milestone) }
+    let(:params) { { board_id: board1.id, from_list_id: list2.id, to_list_id: backlog.id } }
+
+    it 'keeps labels and milestone' do
+      described_class.new(parent, user, params).execute(issue)
+      issue.reload
+
+      expect(issue.labels).to contain_exactly(bug, regression)
+      expect(issue.milestone).to eq(milestone)
+    end
+  end
+
   context 'when moving from closed' do
     let(:issue)  { create(:labeled_issue, :closed, project: project, labels: [bug]) }
     let(:params) { { board_id: board1.id, from_list_id: closed.id, to_list_id: list2.id } }