code: def test_louvain_isolated_nodes():
      is_nx_30_or_31 = hasattr(nx.classes, "backends")
  
      def check(left, right):
          assert len(left) == len(right)
          assert set(map(frozenset, left)) == set(map(frozenset, right))
  
      # Empty graph (no nodes)
      G = nx.Graph()
      if is_nx_30_or_31:
          with pytest.raises(ZeroDivisionError):
              nx.community.louvain_communities(G)
      else:
          nx_result = nx.community.louvain_communities(G)
          cg_result = nxcg.community.louvain_communities(G)
          check(nx_result, cg_result)
      # Graph with no edges
      G.add_nodes_from(range(5))
      if is_nx_30_or_31:
          with pytest.raises(ZeroDivisionError):
              nx.community.louvain_communities(G)
      else:
          nx_result = nx.community.louvain_communities(G)
          cg_result = nxcg.community.louvain_communities(G)
          check(nx_result, cg_result)
      # Graph with isolated nodes
      G.add_edge(1, 2)
      nx_result = nx.community.louvain_communities(G)
      cg_result = nxcg.community.louvain_communities(G)
      check(nx_result, cg_result)
      # Another one
      G.add_edge(4, 4)
      nx_result = nx.community.louvain_communities(G)
      cg_result = nxcg.community.louvain_communities(G)
      check(nx_result, cg_result)
  
label_desc: Use image node_id 1 for calling a global function with example usage: test_louvain_isolated_nodes() without return types