code: def test_null_and_singleton(self, method):
      G = nx.Graph()
      pytest.raises(
          nx.NetworkXError, nx.algebraic_connectivity, G, method=method
      )
      pytest.raises(
          nx.NetworkXError, nx.fiedler_vector, G, method=method
      )
      G.add_edge(0, 0)
      pytest.raises(
          nx.NetworkXError, nx.algebraic_connectivity, G, method=method
      )
      pytest.raises(
          nx.NetworkXError, nx.fiedler_vector, G, method=method
      )
  
imports: from math import sqrt
  import pytest
  import networkx
label_desc: Use image node_id 2 for calling the TestAlgebraicConnectivity obj's underlying member method code with example usage: obj.test_null_and_singleton(method) without return types