docstr: Tests that the subgraph cannot change the graph structure
code: def test_readonly(self):
      """Tests that the subgraph cannot change the graph structure"""
      pytest.raises(nx.NetworkXError, self.H.add_node, 5)
      pytest.raises(nx.NetworkXError, self.H.remove_node, 0)
      pytest.raises(nx.NetworkXError, self.H.add_edge, 5, 6)
      pytest.raises(nx.NetworkXError, self.H.remove_edge, 0, 1)
  
imports: import pytest
  import networkx
  from networkx.utils import edges_equal
label_desc: Use image node_id 9 for calling the TestEdgeSubGraph obj's underlying member method code with example usage: obj.test_readonly() without return types