docstr: Both connected and unconnected nodes should exist
docstr_tok: ["Both","connected","and","unconnected","nodes","should","exist"]
code: def test_all_nodes_exist(self):
      """Both connected and unconnected nodes should exist"""
      sm = StructureModel([("a", "b")])
      sm.add_node("c")
      a_graph = plot_structure(sm)
  
      assert all(
          node in a_graph.get_nodes() for node in ["a", "b", "c"]
      )
  
file_path: causalnex/tests/test_plotting.py
imports: from collections import namedtuple
  from causalnex.plots import EDGE_STYLE, GRAPH_STYLE, plot_structure
  from causalnex.structure import StructureModel
label_desc: Use image node_id 1 for calling the TestToPyvis obj's underlying member method code with example usage: obj.test_all_nodes_exist() without return types