code: def test_nullgraph(self, graph):
      G = graph()
      pytest.raises(nx.NetworkXError, nx.spectral_ordering, G)
  
imports: from math import sqrt
  import pytest
  import networkx
label_desc: Use image node_id 1 for calling the TestSpectralOrdering obj's underlying member method code with example usage: obj.test_nullgraph(graph) without return types