docstr: Should return an isolated node
docstr_tok: ["Should","return","an","isolated","node"]
code: def test_isolates(self):
      """Should return an isolated node"""
  
      nodes = [1, 3, 5, 2, 7]
      sm = StructureModel()
      sm.add_nodes_from(nodes)
      subgraph = sm.get_target_subgraph(1)
      expected_graph = StructureModel()
      expected_graph.add_node(1)
  
      assert set(subgraph.nodes) == set(expected_graph.nodes)
      assert set(subgraph.edges) == set(expected_graph.edges)
  
imports: import pytest
  from networkx.exception import NodeNotFound
  from causalnex.structure import StructureModel
label_desc: Use image node_id 4 for calling the TestStructureModelGetTargetSubgraph obj's underlying member method code with example usage: obj.test_isolates() without return types