change tests based on backend feedback

spec/services/boards/lists/list_service_spec.rb

@@ -9,26 +9,20 @@ describe Boards::Lists::ListService, services: true do
 
   describe '#execute' do
     context 'when the board has a backlog list' do
-      before do
-        create(:backlog_list, board: board)
-      end
+      let!(:backlog_list) { create(:backlog_list, board: board) }
 
       it 'does not create a backlog list' do
-        service.execute(board)
-
-        expect(board.lists.merge(List.backlog)).to eq [board.backlog_list]
+        expect { service.execute(board) }.not_to change(board.lists, :count)
       end
 
       it "returns board's lists" do
-        expect(service.execute(board)).to eq [board.backlog_list, list, board.closed_list]
+        expect(service.execute(board)).to eq [backlog_list, list, board.closed_list]
       end
     end
 
     context 'when the board does not have a backlog list' do
       it 'creates a backlog list' do
-        service.execute(board)
-
-        expect(board.backlog_list).not_to be nil
+        expect { service.execute(board) }.to change(board.lists, :count).by(1)
       end
 
       it "returns board's lists" do