code: def test_dls_preorder_nodes(self):
      assert list(
          nx.dfs_preorder_nodes(self.G, source=0, depth_limit=2)
      ) == [0, 1, 2]
      assert list(
          nx.dfs_preorder_nodes(self.D, source=1, depth_limit=2)
      ) == ([1, 0])
  
imports: import networkx
label_desc: Use image node_id 2 for calling the TestDepthLimitedSearch obj's underlying member method code with example usage: obj.test_dls_preorder_nodes() without return types