Does not allow Backlog/Done lists to be removed

app/services/boards/lists/destroy_service.rb

@@ -7,6 +7,8 @@ module Boards
       end
 
       def execute
+        return false unless list.label?
+
         list.with_lock do
           reorder_higher_lists
           remove_list

spec/factories/lists.rb

@@ -4,4 +4,16 @@ FactoryGirl.define do
     label
     sequence(:position)
   end
+
+  factory :backlog_list, parent: :list do
+    list_type :backlog
+  end
+
+  factory :label_list, parent: :list do
+    list_type :label
+  end
+
+  factory :done_list, parent: :list do
+    list_type :done
+  end
 end

spec/services/boards/lists/destroy_service_spec.rb

@@ -5,26 +5,42 @@ describe Boards::Lists::DestroyService, services: true do
     let(:project) { create(:project_with_board) }
     let(:board)   { project.board }
 
-    it 'removes list from board' do
-      list = create(:list, board: board)
-      service = described_class.new(project, list_id: list.id)
+    context 'when list type is label' do
+      it 'removes list from board' do
+        list = create(:label_list, board: board)
+        service = described_class.new(project, list_id: list.id)
+
+        expect { service.execute }.to change(board.lists, :count).by(-1)
+      end
+
+      it 'decrements position of higher lists' do
+        list1 = create(:backlog_list, board: board, position: 1)
+        list2 = create(:label_list, board: board, position: 2)
+        list3 = create(:label_list, board: board, position: 3)
+        list4 = create(:label_list, board: board, position: 4)
+        list5 = create(:done_list, board: board, position: 5)
+
+        described_class.new(project, list_id: list2.id).execute
 
-      expect { service.execute }.to change(board.lists, :count).by(-1)
+        expect(list1.reload.position).to eq 1
+        expect(list3.reload.position).to eq 2
+        expect(list4.reload.position).to eq 3
+        expect(list5.reload.position).to eq 4
+      end
     end
 
-    it 'decrements position of higher lists' do
-      list1 = create(:list, board: board, position: 1)
-      list2 = create(:list, board: board, position: 2)
-      list3 = create(:list, board: board, position: 3)
-      list4 = create(:list, board: board, position: 4)
-      list5 = create(:list, board: board, position: 5)
+    it 'does not remove list from board when list type is backlog' do
+      list = create(:backlog_list, board: board)
+      service = described_class.new(project, list_id: list.id)
+
+      expect { service.execute }.not_to change(board.lists, :count)
+    end
 
-      described_class.new(project, list_id: list2.id).execute
+    it 'does not remove list from board when list type is done' do
+      list = create(:done_list, board: board)
+      service = described_class.new(project, list_id: list.id)
 
-      expect(list1.reload.position).to eq 1
-      expect(list3.reload.position).to eq 2
-      expect(list4.reload.position).to eq 3
-      expect(list5.reload.position).to eq 4
+      expect { service.execute }.not_to change(board.lists, :count)
     end
   end
 end